# Anyone Tried Using One Tweeter?



## Patrick Bateman

Has anyone on the forum tried running a system with a single tweeter, instead of two?

According to recent psychoacoustics research, _"Popular opinion on the topic of consumer audio systems is that low frequencies are “ hard to localize,” a nd thus can be reproduced by a mono sub woofer in some non-critical location. However, a paper discussing DTS’ technique for encoding surround 
sound (Smyth, 1999) stated that “ experimental evidence suggests that it is difficult to localize mid-to-high frequency signals above about 2.5 kHz” (p. 18). Smyth continues, commenting that when a listener is presented with concurrent low and high frequency information, that high frequencies are relatively unimportant for proper image localization. His statement seemed to oppose what is popularly said about localization, and prompted the preliminary research for this thesis."*_

Here's my understanding of how this would work in our cars:

Let's say that you have a woofer and a tweeter in the kick panel of your car. The woofer covers everything below 1khz, and the tweeter covers everything above 1khz. (This is a simplification - bear with me.)

Below 1khz our perception of the soundstage is dominated by pathlength. Due to this, the depth and the width of the soundstage is largely determined by the location of the woofer. This is counter-intuitive but true, and well documented in numerous texts on psychoacoustics.

Above 1khz, our perception of the soundstage is dominated by frequency response. Have you ever fiddled with the balance knob on your head unit, and noticed that you can move the highs around, but not the lows? For instance, you can move the knob almost all the way to the right, but you can still tell that your woofers are playing, while the high frequencies are dragged over the passenger side? If you can relate to that, then you experienced this phenomenon. It's easier to "trick" our brains into thinking that high frequencies are coming from somewhere else, because our hearing mechanism is sensitive to frequency response above 1khz.

Now running a single tweeter seems quite bizarre, and it's certainly unconventional. But there ARE some compelling reasons to do it. Here's some food for thought:


If your tweeter is in the kick panel, the soundstage will vary on whether there are two people in the car, due to reflections. This is the #1 reason that I personally mount tweeters on the dash.
If your tweeter is in the A-Pillar the soundstage is skewed towards the driver's side, because it's too close. Increasing the level on the opposite tweeter improves the image, but at the expense of the passenger side.
The side window in a car creates a really nasty reflection. Mounting a single tweeter in the center avoids the reflection entirely.
The depth and the width of the soundstage is largely determined by the location of the woofers. Dual tweeters are ideal, but only if their levels are equal. Because we're too close to one, and too far from the other, a single mono tweeter may be the best compromise of all.

Thoughts?

On the surface, I recognize that this sounds like crazy talk. And it isn't something that I would recommend for the home, because at home we sit equidistant from the speakers. But in the car it's really worth consideration. Keep in mind, this isn't a true "center channel." The thing that I don't like about center channels is that they make the soundstage narrower and shallower. But keep in mind that width and depth is determined by the woofer location, not the tweeter. That's why we DON'T want low frequencies in the middle.

* http://mue.music.miami.edu/thesis/robert_hartman/robert_hartman_thesis.pdf(pg 88)


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## Maglite

Time alignment will adjust when you hear the sound that is furthest from your ear.

You could intall a center speaker and run surround sound.


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## Mooble

I think the localization effect definitely decreases as you go higher. I can barely tell from where a 4k test tone originates. 1k is a completely different story. There is a HUGH amount of vocal information from 1k up. 

I think your idea would have some merit if you ran mids and woofers up to 3k with a single center mounted super tweeter. Any less and you are going to miss lots of stereo vocal cues.


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## chithead

What about having both tweeters centralized? That is something I experimented with the dash of my Ram and had good results (thinking it has something to do with how deep the dash is and putting more distance between the tweeter and the ear).


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## mosconiac

Are we evolving to a point where the most critical driver will be the one that covers 200-1.5k? That would be in contrast to typical systems where the mid is (haphazardly) placed in the doors (OEM & aftermarket). Obviously the more esoteric systems place the mids in the kickpanels or near the pillars. Maybe that's why the home audio guys are so focused on getting the midrange right.


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## dlechner

This theory reminds me of some of the JL demo cars. Interesting indeed!


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## dlechner

This is the one that I was thinking of.


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## lycan

interesting ... couple random thoughts:

- the ear recognizes _height_ from the treble, and from the treble alone, because height cues can only arise from the outer ear shape (outer ears being the only thing that ruins the symmetry of our heads as spheres with holes in the sides) ... and outer ear dimensions dictate that only _treble_ wavelengths can be effected by these appendages. HOWEVER ... these height cues must also be MONO in nature, since our two outer ear shapes are virtually identical (unlike owls, for example, who actually hear height in stereo ... helps them hunt in 3D). Bottom line : a single tweeter, mounted up high on the dash, is all you need for stage height!

- a "dumb center", like L+R, must necessarily reduce stage width, tis true. But a "steered center", as in PLII or Logic7, will not reduce width.

- i like the idea of avoiding side window reflections 

- you can help the "side bias" problem by taking advantage of off-axis attenuation ... in other words, careful aiming of the drivers. You can't simultaneously attenuate the "near side" speaker for _both_ front seat passengers ELECTRONICALLY, but you can accomplish a crude approximation MECHANICALLY.


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## mitchyz250f

I was actually thinking about this a couple of months ago after reading this link you posted; The Virtual Acoustics Project in the ISVR: Optimal Source Distribution

There is an image where the tweeters are only seperated by 6.2 degrees appart. With a speaker on the center dash (3 ft approx.) the seperation between left and right tweet would only be 4" or so (just guessing, someone else can do the math).


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## mitchyz250f

Is there a point where the frequency is so high that time alighnment is no longer critical?


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## Patrick Bateman

Mooble said:


> I think the localization effect definitely decreases as you go higher. I can barely tell from where a 4k test tone originates. 1k is a completely different story. There is a HUGH amount of vocal information from 1k up.
> 
> I think your idea would have some merit if you ran mids and woofers up to 3k with a single center mounted super tweeter. Any less and you are going to miss lots of stereo vocal cues.


Yep, that was the idea I was thinking of. A very carefully optimized tweeter mounted in the center of the dash, crossed over at 5khz, and covering a little under three octaves (5-30khz.)

And just to re-iterate, I wouldn't recommend this if it wasn't for the fact that we're way too close to one speaker, and it's difficult to balance the sound from two tweeters.


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## 94VG30DE

lycan said:


> - you can help the "side bias" problem by taking advantage of off-axis attenuation ... in other words, careful aiming of the drivers. You can't simultaneously attenuate the "near side" speaker for _both_ front seat passengers ELECTRONICALLY, but you can accomplish a crude approximation MECHANICALLY.


So in this example, are you suggesting employing a tweeter that would beam quickly (or at a pre-determined point) so that off-axis response was attenuated evenly for both driver and passenger? This is a really interesting idea. Seems like one source for image that is completely symmetrical for both listeners would help the normally difficult task of balanced listening for _two_ occupants in the vehicle.


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## I800C0LLECT

Funny, my first thought was...THIS IS GENIUS!! Then I thought about having a mono tweeter? What if we bring back the L-R from rear fill and apply it to this scenario?

I apologize if this is redundant...not familiar with L7 or pL 2




lycan said:


> interesting ... couple random thoughts:
> 
> - the ear recognizes _height_ from the treble, and from the treble alone, because height cues can only arise from the outer ear shape (outer ears being the only thing that ruins the symmetry of our heads as spheres with holes in the sides) ... and outer ear dimensions dictate that only _treble_ wavelengths can be effected by these appendages. HOWEVER ... these height cues must also be MONO in nature, since our two outer ear shapes are virtually identical (unlike owls, for example, who actually hear height in stereo ... helps them hunt in 3D). Bottom line : a single tweeter, mounted up high on the dash, is all you need for stage height!
> 
> *- a "dumb center", like L+R, must necessarily reduce stage width, tis true. But a "steered center", as in PLII or Logic7, will not reduce width.*
> 
> - i like the idea of avoiding side window reflections
> 
> - you can help the "side bias" problem by taking advantage of off-axis attenuation ... in other words, careful aiming of the drivers. You can't simultaneously attenuate the "near side" speaker for _both_ front seat passengers ELECTRONICALLY, but you can accomplish a crude approximation MECHANICALLY.


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## Patrick Bateman

lycan said:


> interesting ... couple random thoughts:
> 
> - the ear recognizes _height_ from the treble, and from the treble alone, because height cues can only arise from the outer ear shape (outer ears being the only thing that ruins the symmetry of our heads as spheres with holes in the sides) ... and outer ear dimensions dictate that only _treble_ wavelengths can be effected by these appendages. HOWEVER ... these height cues must also be MONO in nature, since our two outer ear shapes are virtually identical (unlike owls, for example, who actually hear height in stereo ... helps them hunt in 3D). Bottom line : a single tweeter, mounted up high on the dash, is all you need for stage height!
> 
> - a "dumb center", like L+R, must necessarily reduce stage width, tis true. But a "steered center", as in PLII or Logic7, will not reduce width.
> 
> - i like the idea of avoiding side window reflections
> 
> - you can help the "side bias" problem by taking advantage of off-axis attenuation ... in other words, careful aiming of the drivers. You can't simultaneously attenuate the "near side" speaker for _both_ front seat passengers ELECTRONICALLY, but you can accomplish a crude approximation MECHANICALLY.


Yes, this is something that didn't occur to me at four in the morning 

If the sound "in the mix" is panned hard to the left or to the right, a mono tweeter is going to screw things up.

So this situation is tricky. With a mono tweeter there WILL be instances when the upper frequency stage isn't realistic.

Maybe three tweeters are the solution, with a steering algorithm? Here are the advantages of three tweeters, as I see it:


Above 1khz, imaging cues are dominated by interlevel differences. In other words, when you're seated too close to one tweeter, and too far from the other, the soundstage is dragged to the door by incorrect ILD. Note that this isn't because one tweeter is too close - it's because one tweeter is *too loud*. This is really REALLY important because we can adjust the level of a tweeter, but *we cannot adjust the location of a midbass*.
Triple tweeters fix this - if 80% of high frequency content are in the center, that's where they'll radiate from.
Below 1khz, imaging cues are dominated by interaural time differences. In other words, when you're too close to one midbass, the soundstage collapses on that side. (This is why we build kickpanels.) As noted in item 1, we can "fix" the tweeter problem by ruining the soundstage for the passenger. But time adjustment is a crude way to repair the problem with ITDs. The best solution is to equalize the pathlengths below 1khz.

In a nutshell, triple tweeters and a steering algorithm is a compelling solution. (JBL MS-8, can you do this?)

I'm still a bit curious about the single tweeter solution however. For instance, I listen to a ton of podcasts, and when I listen to those on the stock system in my car, the soundstage is still stuck on one side of the car. The single tweeter solution seems to offer a solid image on the center of the dash, instead of the unnatural presentation where the sound is stuck to the door.

Note that the balance control *can't* fix this because it only changes ILDs, not ITDs.

A configuration like this also offers some interesting options that aren't practical with dual tweeters. For instance, how about this:

*Possible Configuration?*
*Super Tweeter - 5khz to 30khz*​A super tweeter mounted on a ninety degree waveguide is placed in the center of the dash. Because it's perfectly symmetrical getting the response to sound identical to driver and passenger is trivial, and that's the key to imaging cues above 5khz.
*Wide Range - 300hz to 5khz*​A wide range speaker is used to cover four octaves. Ideally this would be mounted in the kick panels to maximize pathlength. Using one speaker to cover this range solves two problem. First of all, by limiting its output to 300hz and higher, we don't need a speaker with a ton of displacement. There are literally hundreds of three and four inch woofers that can belt out 110dB in a small sealed box, and it's easy to mount in a kick panel.








This Tangband is a good example - a pair of these fit in a box the size of your palm, and will generate 116dB if you limit them to 300hz and higher.
*Midbass - 80hz to 300hz*​By seperating the midbass from the widerange, we can get away with mounting options which aren't ideal for a midrange, like the car doors, or the rear quarter panel, or even the floor. By "breaking out" the midbass and midrange we can get away with very large displacement midbasses. You basically get dynamics AND soundstaging.
*Bass - 80hz and down*​Well this part is easy.


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## Patrick Bateman

94VG30DE said:


> So in this example, are you suggesting employing a tweeter that would beam quickly (or at a pre-determined point) so that off-axis response was attenuated evenly for both driver and passenger? This is a really interesting idea. Seems like one source for image that is completely symmetrical for both listeners would help the normally difficult task of balanced listening for _two_ occupants in the vehicle.


That was the idea behind this thread:
http://www.diymobileaudio.com/forum/diy-mobile-audio-sq-forum/60146-creating-perfect-soundstage.html

When I tried to do it, I ran into a problem where you need a very narrow directivity waveguide to pull off this "hat trick." With a wide directivity waveguide the closer tweeter is too loud.

The problem is that a narrow directivity waveguide gets to be REALLY huge. (The wider it is, the shallower and smaller it is.)









That's why the JBL waveguides look like this.


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## stills

a 2.5 way?


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## lycan

nobody latched on to the owl comment?  it's true, ya know 

Neat thing about the mono tweet idea that Patrick is offering, should be easy to experiment!


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## Se7en

Patrick Bateman said:


> That was the idea behind this thread:
> http://www.diymobileaudio.com/forum/diy-mobile-audio-sq-forum/60146-creating-perfect-soundstage.html
> 
> When I tried to do it, I ran into a problem where you need a very narrow directivity waveguide to pull off this "hat trick." With a wide directivity waveguide the closer tweeter is too loud.
> 
> The problem is that a narrow directivity waveguide gets to be REALLY huge. (The wider it is, the shallower and smaller it is.)
> 
> 
> 
> 
> 
> 
> 
> 
> 
> That's why the JBL waveguides look like this.


Please excuse my ignorance but couldn't you try something that already has a very limited dispersion pattern (like a ribbon mounted horizontally) to attain narrow directivity?


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## ryan s

lycan said:


> interesting ... couple random thoughts:
> 
> - the ear recognizes _height_ from the treble, and from the treble alone, because height cues can only arise from the outer ear shape (outer ears being the only thing that ruins the symmetry of our heads as spheres with holes in the sides) ... and outer ear dimensions dictate that only _treble_ wavelengths can be effected by these appendages. HOWEVER ... these height cues must also be MONO in nature, since our two outer ear shapes are virtually identical (unlike owls, for example, who actually hear height in stereo ... helps them hunt in 3D). Bottom line : a single tweeter, mounted up high on the dash, is all you need for stage height!
> 
> - a "dumb center", like L+R, must necessarily reduce stage width, tis true. But a "steered center", as in PLII or Logic7, will not reduce width.
> 
> * - i like the idea of avoiding side window reflections *
> 
> - you can help the "side bias" problem by taking advantage of off-axis attenuation ... in other words, careful aiming of the drivers. You can't simultaneously attenuate the "near side" speaker for _both_ front seat passengers ELECTRONICALLY, but you can accomplish a crude approximation MECHANICALLY.





Patrick Bateman said:


> That was the idea behind this thread:
> http://www.diymobileaudio.com/forum/diy-mobile-audio-sq-forum/60146-creating-perfect-soundstage.html
> 
> When I tried to do it, I ran into a problem where you need a very narrow directivity waveguide to pull off this "hat trick." With a wide directivity waveguide the closer tweeter is too loud.
> 
> The problem is that a narrow directivity waveguide gets to be REALLY huge. (The wider it is, the shallower and smaller it is.)
> 
> That's why the JBL waveguides look like this.


That's what I was thinking as I read this...the waveguide would need to be large up on the dash...and then there's the "gauge hump" on the driver's side...

What would be a good way to overcome that? Should the tweeter be placed off-center due to the uneven dash surface? 

Just trying to get my head around all this 





Mooble said:


> There is a *HUGH *amount of vocal information from 1k up.


Off topic...there's a person who does a couple garage sales every year, using the same sign..."Hugh Sale <-" :laugh: I lol every time 

Back to the action...


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## lycan

Se7en said:


> Please excuse my ignorance but couldn't you try something that already has a very limited dispersion pattern (like a ribbon mounted horizontally) to attain narrow directivity?


not a terrible idea, in my view, but the off-axis dispersion of the ribbon will "drop like a rock" ... probably not quite optimal.

I think it's an interesting question to ask : what would the _ideal_ dispersion look like for dash mounted tweets? Certainly some degree of off-axis attenuation is welcome to combat side bias (and reflections), and you'd probably like that off-axis attenuation to be largely frequency-independent ... again, to accomplish what that electronic balance control can't (near-side attenuation for both front passengers simultaneously). But too much attenuation, and too sharp a drop as frequency increases, is probably not ideal.

The "right" waveguide is what's called for, i think. But, as Patrick mentioned, it won't be small ... if you want to start shaping the polar response in the lower treble.


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## Patrick Bateman

Se7en said:


> Please excuse my ignorance but couldn't you try something that already has a very limited dispersion pattern (like a ribbon mounted horizontally) to attain narrow directivity?


Ribbons don't have narrow directivity because they're ribbons;
ribbons have narrow directivity because they have a large radiating surface.

So, yes, you *could* use a relatively large diaphragm to narrow the directivity.
Or you could use a waveguide.
Or you could use both 

The problem of using a large diaphragm WITHOUT a waveguide and phase plug is that the high frequencies cancel in front of the cone, and it screws up your polar response. Basically the bigger the diaphragm is, the more you need a waveguide and a phase plug.
































​Check out these two speakers. They're almost identical, but one is two inches, and one is three inches. See how there's a peak in the off-axis response of both, *but the peak is lower in frequency* with the bigger driver? (It's 20khz on the 2", and 12khz on the 3".)

That's because there's no phase plug.

The key to these graphs is that the off-axis response of both drivers is *fantastic* below 10khz. There's a reason that they never publish polar plots of ribbons - they don't perform this nice off-axis.

Both of these are great candidates for the midrange scheme mentioned above, where well-controlled on AND off-axis response is important to preserve imagine cues and improve the power response.


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## Patrick Bateman

ryan s said:


> That's what I was thinking as I read this...the waveguide would need to be large up on the dash...and then there's the "gauge hump" on the driver's side...
> 
> What would be a good way to overcome that? Should the tweeter be placed off-center due to the uneven dash surface?
> 
> Just trying to get my head around all this
> 
> 
> 
> Off topic...there's a person who does a couple garage sales every year, using the same sign..."Hugh Sale <-" :laugh: I lol every time
> 
> Back to the action...


I don't think the waveguide has to be really large with a center-mounted tweeter, and I don't think the shape on the dash will make much of a difference. Here's why:

We're bringing the supertweeter in at 5khz. To control directivity down to 5khz, you need a waveguide that's 2.7" in diameter. That's it! 

The *shape* of the waveguide, and the use of a real compression driver is essential. At these ultra-short wavelengths you need an excellent phase plug. Dome tweeters are out of the question.

Here's the great part - if you use a very good waveguide, you can deeply attenuate the energy that's radiated to the sides, and this will virtually eliminate the audibility of reflections off the left and right window.















The pic above is a six dollar QSC waveguide, and the measurement below is a measurement of the on and off-axis frequency response of the waveguide with a $45 Celestion compression driver. Check out the polar response above 10khz - it's virtually perfect. It's not flat, but that's ok, we can EQ it flat. The key is that it doesn't matter if you're listening on or off axis, the sound is the same.

(Ignore the comments in the measurement, they're from another project I did.)

Anyways, you could easily hack the QSC waveguide down to a manageable size, maybe 3-5" across, and you've got a heck of a supertweeter for about fifty bucks.

























[/img]http://lh4.ggpht.com/_wUDOCViv9D0/S0ZFuFFR14I/AAAAAAAACaE/LAshZJSpq1Y/s800/monoWg2.jpg[/img]















​Here's a few pics of the Celestion compression driver and the QSC waveguide, on the dash of my Accord. The first thing you'll notice is that it's just absurdly large. The reason I took all the horizontal pics is to show that the curve of the dash and the windshield can replace 75% of the waveguide. You can literally hack off the top and bottom with impunity. I think you could get it down to about 2" tall. The very last pic shows my corner mounted waveguides, where I do just that. You can see that it's possible to dramatically reduce the waveguide's footprint, while maintaining directivity control. The key is to work with the boundaries you're given.

(Also, check out how good those new pix look. Someone bought themselves an SLR for Christmas! )

The key is that polar response - this thing is going to sound _exactly the same_ for driver and passenger. And that's the key to a solid center image.


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## fury

This is a response to the supertweeter thread, and this one combined.

I have my tweeters set up in my a-pillars, firing approx at the opposite windscreen.
Yes I know it's not ideal but getting any more angle on these would involve sacrificing forward vision which is highly undesirable.








Here is a picture to give you an idea.

Now I have tried both ScanSpeak Ring Radioators, as well as the ScanSpeak AirCircs, purely because of their different polar responses.

My observations are that the ring radiators definately image better. There is less "blur" to the image. I'd imagine that this would be due to less reflections off the windscreen, due to poorer off axis response.
The issue I had with these though, is that the near tweeter had poorer high frequency response, and this was noticable when objects panned from left to right (there would be tonality change as HF rolled off on the near tweeter).

So I thought i'd throw in the AirCircs in place, bacause of their much better(?) off axis response... The difference was instantly noticably. Tonality from the near/far tweeter was more even, and the near tweeter no longer sounded like it cut out after about 10k.
Problem being with more reflections off the windscreen, the image lost some of its sharpness, and became more blurred.

Ultimately i'd like to rebuild the pillars and aim the tweeters between the driver/passenger, to try and even out the response (probably a tad more towards the passenger to try and even out the volume difference, even if slight) however this will inhibit forward vision and make the apillars quite obtrusive.

My next line of thinking is to create some nicely shaped pieces of foam and stick them between the tweeter and the windscreen, to try and attenuate some of sound before it hits the windscreen, in the hope to reduce some reflections... although I can only see this attenuating a few db at best...

This got me thinking about what sort of directivity we'd like in a car...
Due to the positioning of drivers (closer to one side then the other), we would want something with an asymmetrical polar response. We would ideally want the same frequency response for both side, however we would want the far side to be slightly louder then the near side, to accomodate for the difference in distance between listener and driver. We would then want response to drop off at the outer extremeties of the driver and passenger... So probably drop off sooner on the near side, and later on the far side.

This i believe is what some of the car audio waveguides/horns (USD/ImageDynamics) are designed to do (although they do create their own problems), so I am considering looking into these a little bit...

Just my 2c I guess...


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## gitmobass

Wow, I've learned more from this thread than I have from anything else today! Very interesting stuff...


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## kp89gt

Would it be a single tweeter using a summed L+R? I know some amps, when running mono, only use the information from the Left input and don't do a L+R summing internally.


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## mvw2

I really can't see ever using a single driver when the content is not dominantly mono. Definite left and right information need definite left and right drivers. I could see 3 tweeters using a dedicated center playing combined left-right content and attenuated appropriately, but I can't see a single center alone without saying goodbye to all stage presence.

If reflection and directionality are concerns, why not control them in other ways. For example, open cell foam, even of a relatively thin piece absorbs high frequencies well. It's pointless for woofers, but for tweeters, it's viable. There's dB loss of course as you're soaking up a section of the output rather then reflecting it, but it might be easier and more compact to get the same results. 

Fury, you'd have to use separate left and right EQing to fix the response. Different off-axis angles requires different EQ settings. Same goes for the woofer. For example, if you have the woofer and tweeter crossed at 3kHz with the near woofer at 60 degrees off-axis and the far woofer 30 degrees off-axis, you should expect to need to add a few dB on the near woofer between 2kHz and 3kHz and add, depending on roll-off, a few dB above 6kHz on the near tweeter too to simply offset the drop from the off-axis angle. You can get around this quite a bit by using woofers and tweeters with excellent dispersion characteristics that minimally roll off at medium to high angles. For example, the TBI HDSS tweeters have outstanding off-axis response.


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## fury

You generally don't want a summing for a center...
You want what is common between the left and the right channels.


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## fury

mvw2 said:


> Fury, you'd have to use separate left and right EQing to fix the response. Different off-axis angles requires different EQ settings. Same goes for the woofer. For example, if you have the woofer and tweeter crossed at 3kHz with the near woofer at 60 degrees off-axis and the far woofer 30 degrees off-axis, you should expect to need to add a few dB on the near woofer between 2kHz and 3kHz and add, depending on roll-off, a few dB above 6kHz on the near tweeter too to simply offset the drop from the off-axis angle. You can get around this quite a bit by using woofers and tweeters with excellent dispersion characteristics that minimally roll off at medium to high angles. For example, the TBI HDSS tweeters have outstanding off-axis response.


The problem with EQ, is that if the close tweeter hass smooth FR from the opposite side, then eqing it say +5db at 10khz to get it smooth for the close side, creates a peak in the far side.

This is why we need controlled directivity, where FR is the same for both seats, so eqing one side would create the same FR on the other side.

Tweeters with better off axis response does make the driver/passenger response more uniform, but also creates its own set of problems (reflections and what not).


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## rawdawg

fury said:


> My next line of thinking is to create some nicely shaped pieces of foam and stick them between the tweeter and the windscreen, to try and attenuate some of sound before it hits the windscreen, in the hope to reduce some reflections... although I can only see this attenuating a few db at best...


Todd, the SoCal MECA dude, fabbed up some removable plates lined with foam that specifically soak up high frequencies bouncing off the side windows. There is a pronounced difference in the focus & clarity of the music when those plates are on or off. I mused about having A-pillars with a pronounced slope on the windshield side to soak up frequencies that were bound for reflection hell. You know, something elegant and that didn't block critical road view.

Still musing...


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## ryan s

Patrick Bateman said:


> I don't think the waveguide has to be really large with a center-mounted tweeter, and I don't think the shape on the dash will make much of a difference. Here's why:
> 
> We're bringing the supertweeter in at 5khz. To control directivity down to 5khz, you need a waveguide that's 2.7" in diameter. That's it!
> 
> The *shape* of the waveguide, and the use of a real compression driver is essential. At these ultra-short wavelengths you need an excellent phase plug. Dome tweeters are out of the question.
> 
> Here's the great part - if you use a very good waveguide, you can deeply attenuate the energy that's radiated to the sides, and this will virtually eliminate the audibility of reflections off the left and right window.
> 
> 
> ​The pic above is a six dollar QSC waveguide, and the measurement below is a measurement of the on and off-axis frequency response of the waveguide with a $45 Celestion compression driver. Check out the polar response above 10khz - it's virtually perfect. It's not flat, but that's ok, we can EQ it flat. The key is that it doesn't matter if you're listening on or off axis, the sound is the same.
> 
> (Ignore the comments in the measurement, they're from another project I did.)
> 
> Anyways, you could easily hack the QSC waveguide down to a manageable size, maybe 3-5" across, and you've got a heck of a supertweeter for about fifty bucks.
> 
> Here's a few pics of the Celestion compression driver and the QSC waveguide, on the dash of my Accord. The first thing you'll notice is that it's just absurdly large. The reason I took all the horizontal pics is to show that the curve of the dash and the windshield can replace 75% of the waveguide. You can literally hack off the top and bottom with impunity. I think you could get it down to about 2" tall. The very last pic shows my corner mounted waveguides, where I do just that. You can see that it's possible to dramatically reduce the waveguide's footprint, while maintaining directivity control. The key is to work with the boundaries you're given.
> 
> (Also, check out how good those new pix look. Someone bought themselves an SLR for Christmas! )
> 
> The key is that polar response - this thing is going to sound _exactly the same_ for driver and passenger. And that's the key to a solid center image.


How easy/difficult/necessary would it be to have the waveguide match the curvature of the windshield and dash, if one were to stick the tweeter way up near the defrost vents?


Nice choice on the Pentax, by the way!


----------



## jp88

You once again have me very interested Patrick. It seems that you and I are on similar paths. 

Whats to say you couldn't use this tweeter instead of 5k and up 10k and up, and for midrange use my Frankenstein test, from 500 hz to 10k?

I finally got a couple pics of my Frankenstein setup uploaded to pb Pardon the dust on my dash, and the very unfinished nature of the test mules.


----------



## Se7en

fury said:


> You generally don't want a summing for a center...
> You want what is common between the left and the right channels.


What if you could re-process the music so that the signal being sent to the center was specific only to the center channel and not shared between the left and right (or common between L/R). Meaning true discrete 3 way. This would also mean that left and right channels would only play information that was specific to left or right , similarly, left channel would contain no right channel information either vice versa.

I only ask because I was reading up on a "trinaural" processor designed to do just this. Separate a 2 channel signal into 3 discrete channels while removing all crosstalk between L/R channels.


----------



## TREETOP

Interesting that this thread came up, because I was giving this some thought a couple weeks ago. My right side tweeter failed (combination of manufacturing/design flaw and experimentally using it beyond its capabilities), and while my center focus shifted to the left some it also got more precise- decay of cymbal crashes, for example, was way more sanitary. Stage wasn't drawn as far left as I'd expect, and my stage was still high. There were a few times I even ran the balance to the right because I could swear I heard highs from that side.

My tuning isn't currently spot-on because the setup is temporary, and i do have some reflections that I'm battling (large center console, tweets in the doors) but beyond that I was shocked and confused about why it didn't sound way more out of balance than it did.

Quite a few months ago I lost a left-side tweeter, and it was annoying as hell- I could barely listen to it- stage was far right and very low. This time with a right side tweeter gone, it wasn't nearly as bad- in fact it was almost enjoyable. Embarrassing to say that, but it was a strange phenomenon that I wouldn't mind learning more about.


----------



## fury

Se7en said:


> What if you could re-process the music so that the signal being sent to the center was specific only to the center channel and not shared between the left and right (or common between L/R). Meaning true discrete 3 way. This would also mean that left and right channels would only play information that was specific to left or right , similarly, left channel would contain no right channel information either vice versa.
> 
> I only ask because I was reading up on a "trinaural" processor designed to do just this. Separate a 2 channel signal into 3 discrete channels while removing all crosstalk between L/R channels.


I believe this is what you'd want if you were doing a 3.1 setup.

Processors like the Alpine PXA H700/701/900 can all do this.... Unfortunately these are no longer being made...
The MS-8 i believe should be able to do this, but is not available yet...

Not sure of any other car audio specific processor capable and available.


----------



## lycan

clarification about ribbons is in order, methinx ...

It's an inaccurate generalization to suggest that ribbons have bad polar response, and equally inaccurate to suggest that it's because of a large radiating area. In reality, ribbons have a _great_ off-axis response in _one_ dimension, and a _terrible_ off-axis response in the _other_ dimension. This is because the ribbon is long in one dimension, and short in the other 

Remember ... ALWAYS REMEMBER ... a radiating surface is nothing but an array of point sources, laterally displaced in TWO dimensions. If you understand that delayed point sources give rise to destructive interference, if you understand comb filtering, then you understand the polar response of any driver, or array of drivers.

Imagine a couple points on a ribbon. Along the long end, points will be laterally displaced by a large distance. Therefore, off-axis response will be sharply attenuated, at a relatively low frequency, IN THIS DIMENSION. But in the other dimension, the radiating point sources are not far apart ... and the off-axis response will be much better 

In short, "radiating area" is too simplistic to describe anything but a circle  Ribbons radiate widely in one dimension, but narrowly in the other, because ribbons are short in one dimension, but long in the other ... in other words, because they are ribbons


----------



## Se7en

fury said:


> I believe this is what you'd want if you were doing a 3.1 setup.
> 
> Processors like the Alpine PXA H700/701/900 can all do this.... Unfortunately these are no longer being made...
> The MS-8 i believe should be able to do this, but is not available yet...
> 
> Not sure of any other car audio specific processor capable and available.


Actually I think that you're correct. In rereading about the Trinaural processor, it would appear that they key difference is that it actually shares mono information across all 3 channels.

Here's an excerpt:

"Comparison of Dolby pro logic with the Trinaural processor showed the Trinaural processor to sound much cleaner than the Dolby process. Deployment of instruments in the soundstage appears to more varied. The Dolby process uses steering logic to ensure that center images appear only in the center (LR cut off). This is required for movie dialog, but the steering logic affects musical reproduction negatively. On the other hand, the Trinaural processor presents a mono signal in all three channels, spreading the sound across the entire sound stage. This leakage of mono signals into L and R when using the Trinaural processor is an artifact of some of the second-order correction mechanisms applied in the Trinaural to mitigate effects of real rooms and real recordings. The L and R leakage effect is not noticeable on stereo recordings, where the center is very well defined using the Trinaural processor."


----------



## Se7en

lycan said:


> clarification about ribbons is in order, methinx ...
> 
> It's an inaccurate generalization to suggest that ribbons have bad polar response, and equally inaccurate to suggest that it's because of a large radiating area. In reality, ribbons have a _great_ off-axis response in _one_ dimension, and a _terrible_ off-axis response in the _other_ dimension. This is because the ribbon is long in one dimension, and short in the other
> 
> Remember ... ALWAYS REMEMBER ... a radiating surface is nothing but an array of point sources, laterally displaced in TWO dimensions. If you understand that delayed point sources give rise to destructive interference, if you understand comb filtering, then you understand the polar response of any driver, or array of drivers.
> 
> Imagine a couple points on a ribbon. Along the long end, points will be laterally displaced by a large distance. Therefore, off-axis response will be sharply attenuated, at a relatively low frequency, IN THIS DIMENSION. But in the other dimension, the radiating point sources are not far apart ... and the off-axis response will be much better
> 
> In short, "radiating area" is too simplistic to describe anything but a circle  Ribbons radiate widely in one dimension, but narrowly in the other, because ribbons are short in one dimension, but long in the other ... in other words, because they are ribbons


Thank you for the clarification.


----------



## lycan

fury said:


> You generally don't want a summing for a center...
> You want what is common between the left and the right channels.


so true ...

sadly, you can't accomplish this with simple algebra 

you need steering logic.


----------



## Patrick Bateman

fury said:


> I believe this is what you'd want if you were doing a 3.1 setup.
> 
> Processors like the Alpine PXA H700/701/900 can all do this.... Unfortunately these are no longer being made...
> The MS-8 i believe should be able to do this, but is not available yet...
> 
> Not sure of any other car audio specific processor capable and available.


Rockford Fosgate RFQ5000 can do it, right? Here's five of them on Ebay:







Rockford Fosgate RFQ5000 Surround Processor RFQ New - eBay (item 350287562245 end time Jan-30-10 22:58:38 PST)

IIRC, Jim Fosgate was the driving force behind Prologic II, and it's even "audiophile approved" 

Stereophile: Jim Fosgate: Of (Surround) Sound Mind

_Guttenberg: I guess this is a good time to ask: What, exactly, is the difference between the original Pro Logic and Pro Logic II?

Fosgate: They both have their roots in quad and SQ matrix-style encoding/decoding. The original Pro Logic had mono "band-limited" surrounds, PLII has "full-bandwidth" stereo surrounds. Since original Pro Logic was a film-oriented system, Dolby had to make sure the center/dialog channel was rock-solid. So they weighted the steering toward the center front channel, which shrank stage width on stereo recordings. When Pro Logic came out, it was a marvel of performance and stability.

Guttenberg: PLII can work its magic on LPs and CDs?

Fosgate: Yes. Please understand that PLII doesn't affect the stereo soundstage, other than to display the in-phase part of the program over the three front channels—the out-of-phase or randomly phased signals are sent to the rear. When switching between stereo and PLII, you'll see that the stereo soundstage stays intact but has greater depth and width. Sometimes you're not even aware of the extra speakers, until you turn them off and the soundstage collapses back to stereo.

Guttenberg: It's more than a little ironic—your invention has made you a wealthy man, but you created this home-theater processor with music in mind. Literally._

An easier option might be a $200 laptop with an SSD hard drive, running Foobar2000. The Fosgate solution would LOOK a heck of a lot better.


----------



## fury

I dont know the specifications of this RF unit, but does it do ta/eq/xover etc... or must all processing be done afterwards?

Looking at it having only a stereo pair of front outputs tells me that it's probably not flexible enough for most cars (without other additional processing).

I'm lucky enough to have an H900, but finding room for a center speaker in my car is another story


----------



## dbiegel

Interesting idea. Most people are actually listening to 4, 8, or more tweeters when you consider all the glass reflections.  The key benefit to what you're proposing is that a properly optimized tweeter placed in the center would get rid of most of the reflections -- so you'd actually go from 4 or 8 tweeters to 1. That's a huge benefit to say the least.

I see two potential downsides: 

(1) You're going to have a large difference in the reflected sound and room interaction between the midrange and the tweeter. Siegfried Linkwitz, for example, is a major proponent that spectral content of reflections should be similar to the direct sound (but attenuated). If not, then the sound source will be localized. Isn't that pretty much the theory behind your designs and a lot of Geddes' work? Anyway, your music will have lots of early and late reflections from the midrange, but practically zero from the tweeter. I can't imagine they'll blend very well acoustically like that... It's pretty much the opposite situation of your unity horn in the high frequencies. (and the midrange too, if the tweeter isn't crossed super steeply)

(2) In doing this, there's an assumption that the high frequency content in music is always "riding on" low frequency content... so that we can localize it based on the low frequencies... but music won't always be like that. Some parts of music won't have lower frequency harmonics to tell your brain where the sound came from..

I say try it anyway though -- the positives may outweigh the negatives depending on your car, especially if you can also minimize the reflections from your midrange.


----------



## thehatedguy

When did science stop using Occam's razor?


----------



## lycan

fury said:


> I dont know the specifications of this RF unit, but does it do ta/eq/xover etc... or must all processing be done afterwards?
> 
> Looking at it having only a stereo pair of front outputs tells me that it's probably not flexible enough for most cars (without other additional processing).
> 
> I'm lucky enough to have an H900, but finding room for a center speaker in my car is another story


H900 = Pro Logic I
RFQ5000 = Pro Logic II


----------



## fury

lycan said:


> H900 = Pro Logic I
> RFQ5000 = Pro Logic II



Ahh very interesting.

Still if using something like the RFQ5000, you'd need to use a DSP (ie: Behringer DCX2496) to do processing after the RFQ... You can feed the FL/FR/C input into the DCX, and have 2-way active setup for FL/FR/C channels if necessary... and sub straight off your headunit?


----------



## mvw2

fury said:


> The problem with EQ, is that if the close tweeter hass smooth FR from the opposite side, then eqing it say +5db at 10khz to get it smooth for the close side, creates a peak in the far side.
> 
> This is why we need controlled directivity, where FR is the same for both seats, so eqing one side would create the same FR on the other side.
> 
> Tweeters with better off axis response does make the driver/passenger response more uniform, but also creates its own set of problems (reflections and what not).


You missed when I said separate left and right EQs. Yes, if you have a single, universal EQ, you're screwed. You have to fix it with proper aiming. If you have separate EQs like say with Pioneer's P800PRS, then you can independently EQ the left and right sides as needed, and you don't get the problem you're speaking of.


----------



## fury

mvw2 said:


> You missed when I said separate left and right EQs. Yes, if you have a single, universal EQ, you're screwed. You have to fix it with proper aiming. If you have separate EQs like say with Pioneer's P800PRS, then you can independently EQ the left and right sides as needed, and you don't get the problem you're speaking of.



I understand what you're saying, but i'm talking about the response from a single tweeter, at 2 positions in the car (drivers seat and passengers seat).
Your solution still will not work.


Let take the FR of the tweeter as an example:









Lets say I aim the tweeter at the passenger, and the driver is then 30 degrees off axis.
The passenger will have a smooth response on axis all the way up to 20khz... Great!
The driver however, will have a from 5k, down about 8db at 20khz.
If I was to equalise this response to give me flat response for the driver (lets say a filter to increase from 5khz and up by 4db/oct), then it would also do the same thing to the passenger side response... so the passenger side response would no longer be flat, it would be rising at 4db/oct from 5khz.

This is highly undesirable, and hence why even power response is so important.


Even if I equalise like you stated above, so that my summed response is flat, my left and right response isnt. This creates tonality shifts from left to right of stage... If something is designed to move on the stage, then it can audible change in tonality due to this... Or instrument (ie: 2 guitars) placed on either side of the stage could sound quite different even though they shouldnt.


----------



## Patrick Bateman

lycan said:


> H900 = Pro Logic I
> RFQ5000 = Pro Logic II


In the world of high end, there seems to be a lot of companies run by retired dentists and lawyers. Basically guys who have a cursory knowledge of audio, but lack the years of dedication and study that are required to understand the ins and outs. (Every time I go to CES I see 50 new audio companies that will be gone by year's end.) Jim Fosgate seems like "the real deal". I generally enjoy equipment made by guys who've devoted their lives to audio. Anyways, I put my money where my mouth is, and bought a Pro Logic II decoder. Should be interesting to see what I can do with it.

Here's another interview with Fosgate, about the differences between the device reviewed by Stereophile and the device sold by Rockford Fosgate.

_"Hi Guys, I am enjoying this, I have been in my world of “heavy design” here in the high Rocky Mountains for a long time, and it’s nice to come up for a breath of fresh air. Thanks for the positive comments. I will answer some questions today and will discuss how matrix decoders work tomorrow, and how my new feedback logic system differs.

When will new products with PL2 start coming out? Dolby is expected to release the digital “C code” in August (next month). I am told at least one IC manufacturer is will be trying to demo it at the next AES convention. The custom analogue ICs will take much longer to become available because of process lead times. The digital version had to be completed before work could begin on the Analogue version. The Rockford Fosgate RFQ5000 DPL2 processor uses “off the shelf” Analogue Device ICs (same as my breadboards); this allowed them to design and build their product quickly. Problem is these devices went out of production just as Rockford started manufacturing, they made a one-time purchase to hold them until they can switch to one of the Dolby custom versions. I am guessing here, but I suppose some digital platforms can accept the new code without a change in hardware, I will verify this with Dolby and update later you on this. If this is possible products could be shown at the winter CES with DPL2. It will take longer for other products.

Will DPL2 work from both analogue and digital inputs? On the digital version this depends on the features offered by the manufacturer; it can work digital direct or with an A to D converter in front of the decoder. One would think that there is an advantage to using “digital in” for digital sources to eliminate as many conversions as possible. The future analogue version will work directly from analogue sources.

Which was more important to me music or film? I must confess music is my favorite. I spend 95% of my time working on it. In fact I always have. I have found it to be the most difficult; when I get the music right the movies are usually right on too. This technology dosent seem to care if something has been surround encoded or not. I work with the nice folks at Dolby on the encoded material. They are very familiar with that material and how it should sound. I listen to lots of movies on the tail end of the design to make sure there are no surprises.

How many channels? It is possible to bring out as many channels with this technology as with any other matrix technology. Dolby and I agree that 5 channels is the best place to start. It’s been hard enough to talk some consumers into 5 channels, let alone 7 to 10. Dolby does not want to confuse the market by bringing this out with more channels now because consumers would think the extra channels were the “big thing” instead of the improved performance. I have worked with more channels on the breadboard but find that 5 channels are all I need in my listening room.

Let me describe my reference room, it is located in the basement (all concrete including the upper ceiling), as far away as possible from the bedroom. I can listen at full throttle in the middle of the night without bothering the wife or neighbors. The room is 34 ft by 24 ft with 10 ft ceiling and 1 foot of fiberglass for a bass trap above a drop ceiling which gives a finished height of 9 feet. Each corner has a small wall made of concrete blocks to form the corner enclosures. Speaker chambers are cast into the concrete wall at the centers of each wall. Total 8 channels. This configuration eliminates the four 90-degree corners and gives me eight 45-degree corners.(less diffraction) The speakers are flush mounted. The enclosures are so big the woofers see a true infinite baffle. I use four ten-inch woofers on each front channel and two on all the other channels. I started with 15-inch woofers but went down to 12 inches, than 10 inches to get tighter bass. There are two 5¼-inch aluminum midrange drivers on each channel. I use one very high efficiency Ring radiator tweeter on each channel. The system is tri-amped with all tubes. The crossovers are passive and are built into the amplifiers as is the required equalization. The amps are all push pull of my own design. The woofer amps are 55 watts each with 12 db NFB. The midrange amps are 55 watts each with 6 db NFB. The tweeter amps are 8 watt all triode with no NFB.(Requires 15 tube amplifiers total for 5 channels) The walls are covered with thick carpet. This configuration gives me very well balanced precision smooth sound, very musical sounding. 

The left and right front channels are mounted so the tweets and mids are about 4.5 feet high. The mids and tweets are mounted below the screen on the center front. The woofers are behind the screen. (May try one of the perforated screens to raise the center, not sure if it will sound better or worse). The two back corner speakers are mounted high in the back corners. All mid and hi range drivers are aimed directly at the sweet spot which is about 4 feet back of center (front to back) and centered (left to right). This system will take me about anywhere I care to go. I found long ago that I could not tell what I was doing in the decoder without a system like this. I can hear the change of even the smallest tweek in the decoder adjustments. I have excellent sidewall images, in fact images all the way around the room. I use only 5 channels now. It was too much trouble to keep the other channels modified (I have gone through many circuit changes in the amplifiers and different drivers in the walls). The 15 tube amps keep me warm on the coldest winter nights,“love the glow of them tubes”. People who have heard it are surprised to hear imaging all around the room with 5 speakers. It works, what else can I say. 

Low bass problem on the surrounds in 6 axis? Yes, because the backs are “out of phase” for the dominant signals in the surrounds, this cancels some of the bass. Sounds good on stereo stuff, but causes this bass problem on movies. On PL2 we fixed this with movie mode that puts backs in-phase.

Will every manufacturer be able to incoporate this technology? Sure will, that is why I am working with Dolby. It will be available to each manufacturer on an equal basis. I hope everyone who wants it to be able to own one. Products will appear in all price ranges, so you will not have to be loaded to enjoy it.

Is this my final solution to this technology or will there be another in a few years? This is probably my swan song. This is what I have been trying to accomplish all these years. Can’t see how I could improve on it.

Tomorrow I will describe how matrix decoders work. See you then."_


----------



## MarkZ

Se7en said:


> What if you could re-process the music so that the signal being sent to the center was specific only to the center channel and not shared between the left and right (or common between L/R). Meaning true discrete 3 way. This would also mean that left and right channels would only play information that was specific to left or right , similarly, left channel would contain no right channel information either vice versa.
> 
> I only ask because I was reading up on a "trinaural" processor designed to do just this. Separate a 2 channel signal into 3 discrete channels while removing all crosstalk between L/R channels.


I've yet to see a good implementation of this. The attempts I've seen in the fourier domain are dreadful. And there are a couple of VST plugins that attempt to do something similar that give rise to digital artifacts.

"Common components" are hard to pull out...


----------



## Patrick Bateman

fury said:


> I understand what you're saying, but i'm talking about the response from a single tweeter, at 2 positions in the car (drivers seat and passengers seat).
> Your solution still will not work.
> 
> 
> Let take the FR of the tweeter as an example:
> 
> 
> 
> 
> 
> 
> 
> 
> 
> Lets say I aim the tweeter at the passenger, and the driver is then 30 degrees off axis.
> The passenger will have a smooth response on axis all the way up to 20khz... Great!
> The driver however, will have a from 5k, down about 8db at 20khz.
> If I was to equalise this response to give me flat response for the driver (lets say a filter to increase from 5khz and up by 4db/oct), then it would also do the same thing to the passenger side response... so the passenger side response would no longer be flat, it would be rising at 4db/oct from 5khz.
> 
> This is highly undesirable, and hence why even power response is so important.
> 
> 
> Even if I equalise like you stated above, so that my summed response is flat, my left and right response isnt. This creates tonality shifts from left to right of stage... If something is designed to move on the stage, then it can audible change in tonality due to this... Or instrument (ie: 2 guitars) placed on either side of the stage could sound quite different even though they shouldnt.


I posted some info on how to get flat response for both driver and passenger here:

http://www.diymobileaudio.com/forum...creating-perfect-soundstage-7.html#post927553

It's easiest to do with a waveguide, but you can do it with a direct radiator too, as long as you limit it to a narrow bandwidth.


----------



## lycan

Patrick Bateman said:


> In the world of high end, there seems to be a lot of companies run by retired dentists and lawyers. Basically guys who have a cursory knowledge of audio, but lack the years of dedication and study that are required to understand the ins and outs. (Every time I go to CES I see 50 new audio companies that will be gone by year's end.) Jim Fosgate seems like "the real deal". I generally enjoy equipment made by guys who've devoted their lives to audio. Anyways, I put my money where my mouth is, and bought a Pro Logic II decoder. Should be interesting to see what I can do with it.


Agreed ... absolutely. Jim Fosgate (the man, not the company that shares his name) is the real deal. He invented Pro Logic II, and as far as i know that makes him one of a very few early pioneers in _steering_ technology for decoding 2-ch into multi-ch audio. I think he even had the car environment in mind as he was developing PLII


----------



## razholio

lycan said:


> nobody latched on to the owl comment?  it's true, ya know


yup. got it and second it. Their ears are at different heights in their skull so they can get a good 2D audio image of their prey and attack right through the cover of snow in the winter.


----------



## epifant

Patrick Bateman said:


> Quote Fosgate: "I started with 15-inch woofers but went down to 12 inches, than *10 inches to get tighter bass*."


----------



## Fast1one

Dammit John, you had to go and post the RFQ5000.

Guess what's in the mail


----------



## Patrick Bateman

Fast1one said:


> Dammit John, you had to go and post the RFQ5000.
> 
> Guess what's in the mail


John?


----------



## lycan

razholio said:


> yup. got it and second it. Their ears are at different heights in their skull so they can get a good 2D audio image of their prey and attack right through the cover of snow in the winter.


but alas, not so for humans 

For our miserable species: height is treble, and height is mono. 

So, if you're thinking something like ... "since height is _mono_, we should be able to use some type of electronic EQ to _raise_ the apparent stage of low mounted drivers, for _both_ front seat listeners!" ... well, that's where you would be right 

(no need to ask, the search function is your friend. IIRC, an AES paper is even referenced)

thanks dood


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## Fast1one

Patrick Bateman said:


> John?


Uhoh am I confusing screen names and real names again


----------



## mitchyz250f

This is way over my head. But I think I am following most of it. 

It seems that most of the benefit could be achieved with two tweeters at the center of the dash as Chithead experimented with and the picture dlechner posted (post 7)? These two tweeters would be off axis the same amount for both passendger and driver. Equalization and TA would be nearly identical for both tweeters. 

Wouldn't that eliminate much of the need for additional data processing such as steering? 

Would our brains identify the similar sounds from both tweeters as mono? 

Also, if you had the mids in the KP, you could get similar path lengths by placing the tweeters at the same PL towards the middle of the dash. 

Am I stating the obvious or am I lost?


----------



## Patrick Bateman

mitchyz250f said:


> This is way over my head. But I think I am following most of it.


It still gives me headaches, but I think it's essential to understand it if we have any hope of creating a decent soundstage. When I see guys putting eights and tens in their car doors, it makes me cringe, because it doesn't work. (Been there, done that.)







The key to all of this is to understand that there's a transition between our perception around 1.6khz. In the one octave between 1khz we have to pay attention to both pathlength and frequency response. But below this octave pathlength is king, and above this octave frequency response rules. This transition is due to the distance between our ears, and their shape. If you want to, get a ruler and measure the distance. You'll see that the dimensions correspond to the frequency. (1600hz is 8.4".)










mitchyz250f said:


> It seems that most of the benefit could be achieved with two tweeters at the center of the dash as Chithead experimented with and the picture dlechner posted (post 7)? These two tweeters would be off axis the same amount for both passendger and driver. Equalization and TA would be nearly identical for both tweeters.
> 
> Wouldn't that eliminate much of the need for additional data processing such as steering?
> 
> Would our brains identify the similar sounds from both tweeters as mono?


Honestly, I am not convinced that we need two tweeters at this point. Above a certain frequency, we're barely able to perceive depth or width. I am trying to figure out what the downsides to a single mono tweeter are, and I'm drawing a blank.

Here's the best I can come up with:


If you use one tweeter instead of two, you must limit it's response to a range where the influence of interaural time delay is inaudible. According to Blauert, this happens above 1600hz. Because our tweeter will have output below the crossover frequency, it would be advisable to increase the crossover point to a frequency above the perceptual "crossover." Perhaps 3200hz, one octave above?
Because interaural intensity differences are critical to soundstaging above 1600hz, if you DO use two tweeters, they MUST match. There are two solutions to this. Either put them both in front of you, where their directivity is similar. Or if you mount them in a different location, juggle their distance, directivity and frequency response so that you end up with the same goal: identical frequency response on the left and the right.

The thing is, it's a helluva lot harder to get two tweeters to sound identical when you're listening to one of them off axis, and their pathlengths are significantly different.

On the contrary, here are the drawbacks of stereo tweeters:

Due to the Haas Effect, the tweeter on the opposite side of the car needs to be about 3-6dB louder. Compounding the problem is the fact that we're already too close to the driver's side tweeter.
We are trying to create a soundstage in front of us. Due to head related transfer functions, when we move tweeters to the door or the kick panels it creates the perception that the sound is in the wrong location. It *is* possible to offset this perception via EQ, but I've never seen anyone publish a good technical article on how to do this. A lot of discussion that talks about a cut here or a boost there, but nothing concrete or widely accepted.
Probably the biggest problem with using two tweeters is that reflections are rarely symmetrical. The reflected energy creates phantom imaging cues. It's like having a 2nd, 3rd, 4th and 5th set of tweeters. Because the cues are not symmetrical, the soundstage dimensions wander. This is particularly problematic when tweeters are mounted low, and the car is occupied by one person and not two. Absorbtion and diffusion of the reflected energy makes an audible improvement, as demonstrated by Eldridge in his 4Runner and by myself in the spherical enclosure thread.
 


mitchyz250f said:


> Also, if you had the mids in the KP, you could get similar path lengths by placing the tweeters at the same PL towards the middle of the dash.
> 
> Am I stating the obvious or am I lost?


The perception of depth and width is due to interaural time delay, and we're not very sensitive to that above 1600hz. Due to that, I'm not certain that the tweeters need to be equidistant to the kick panels. If I were to use mono tweeters, I'd use time delay to sync 'em up with the midrange. Physically moving them is probably overkill.

I wonder how far you could take this. Perhaps a single supertweeter at the top of the windshield, time aligned to the midranges?

In summary, you ask if you used a single tweeter would the music sound like it was in mono. I'd reckon the answer is "no." Your perception of depth and width begins around 1600hz; as long as you locate the midranges and the midbasses carefully, you'll get your cues from them. This isn't to say that you should go home and turn off one of your tweeters however. Based on what I've read, tweeters *do* have a small influence on width and depth, but this is primarily due to the shape of the ear. And as soon as you put your tweeters too far off to the side, or even worse, the floor, you've ruined the illusion. Therefore, one tweeter in an ideal location may trump two tweeters in a less-than-ideal location.

I really need to build something like the JL car and find out.


----------



## lycan

Patrick, search for a thread called "paging wolfie about stage height", or something.

You'll find a reference to an AES paper about spectral manipulation to _raise_ the apparent source location. It works because height cues are mono (our ear shapes are similar, and not located on our foreheads & chins), and related to well-understood HRTF's (mostly related, again, to outer ear shapes ... which is why height is not localizable until the treble).

The techniques, or similar variants, have been used by car audio competitors for _years_. Of course, that won't establish much credit in some corners of the internet  so maybe an AES paper that's not specifically about car audio will


----------



## Patrick Bateman

If the last post has piqued your curiosity, here are some links to read up on. Up until this point I have focused on using waveguides and directivity to control or diffuse early reflections. The next stage in this progression may be the *intentional* use of reflections to widen and deepen the sound stage. For instance, concert halls all over the world use intentional reflections to create an impression of spaciousness and ambiance which makes the music more enjoyable, more intelligible, and less fatiguing.

Here's the links:

Mark Eldridge: Do The Evolution (Jan/Feb 2001)
"From the back edge of the doors all the way around the back of the rear seat area at ear level are custom proprietary acoustical panels. They are designed not to directly reflect nor absorb any sound energy that impacts them, but control the energy in such a way as to aid in the psycho-acoustic illusion of being in a larger listening space. "

Spaciousness
"Spaciousness or spatial impression is a term that was introduced in the 1970s to refer to a listener's feeling of being enveloped in the music. Much research on this concept has occurred in the past three decades, and now two aspects of spaciousness have been identified: Auditory Source Width (ASW) and Listener Envelopment (LE)"

Chapter 2: Spatial Hearing
A bunch of information about how we perceive sounds above, in front, below, and behind us.

Jérôme Daniel's 3D Sound Research : The Experimenter Corner (Hearing Higher Order Ambisonics)
Learning about ambisonics helps to illustrate how we can slice the spectrum into bands, and relocate them

http://mue.music.miami.edu/thesis/robert_hartman/robert_hartman_thesis.pdf
An entire thesis on the subject

http://www.cs.cmu.edu/~lewicki/cp-s08/sound-localization1.pdf
If you read anything on this subject, read the three papers by the last author, and the one paper by the 2nd to last. They're all free downloads.


----------



## lycan

Patrick Bateman said:


> If the last post has piqued your curiosity, here are some links to read up on. Up until this point I have focused on using waveguides and directivity to control or diffuse early reflections. The next stage in this progression may be the *intentional* use of reflections to widen and deepen the sound stage. For instance, concert halls all over the world use intentional reflections to create an impression of spaciousness and ambiance which makes the music more enjoyable, more intelligible, and less fatiguing.
> 
> Here's the links:
> 
> Mark Eldridge: Do The Evolution (Jan/Feb 2001)
> "From the back edge of the doors all the way around the back of the rear seat area at ear level are custom proprietary acoustical panels. They are designed not to directly reflect nor absorb any sound energy that impacts them, but control the energy in such a way as to aid in the psycho-acoustic illusion of being in a larger listening space. "
> 
> Spaciousness
> "Spaciousness or spatial impression is a term that was introduced in the 1970s to refer to a listener's feeling of being enveloped in the music. Much research on this concept has occurred in the past three decades, and now two aspects of spaciousness have been identified: Auditory Source Width (ASW) and Listener Envelopment (LE)"
> 
> Chapter 2: Spatial Hearing
> A bunch of information about how we perceive sounds above, in front, below, and behind us.
> 
> Jérôme Daniel's 3D Sound Research : The Experimenter Corner (Hearing Higher Order Ambisonics)
> Learning about ambisonics helps to illustrate how we can slice the spectrum into bands, and relocate them
> 
> http://mue.music.miami.edu/thesis/robert_hartman/robert_hartman_thesis.pdf
> An entire thesis on the subject
> 
> http://www.cs.cmu.edu/~lewicki/cp-s08/sound-localization1.pdf
> If you read anything on this subject, read the three papers by the last author, and the one paper by the 2nd to last. They're all free downloads.


careful with reflections ... concert hall reflections are most likely at or beyond the Haas (or precedence) limit, whereas the nearfield reflections in a car are _not_. I know you know this, but reflections that are _too close_ in time (or distance) to the primary sound will NOT add spaciousness. They will, however, make localization more difficult and screw-up frequency response with comb nulls 

That's why all the L-R rear-fill threads recommend a delay on the order of 20msec ... this _will_ add spaciousness (yes, it's a "generated" reflection) and _enhance_, rather than _detract_ from, the front stage.

In short: all reflections are not treated (or heard!) equally.


----------



## mitchyz250f

Patrick, what I was suggesting was let’s say you have two tweeters in the center of the dash firing up the windshield or located at the top of the windshield. Left and right tweeter right next to each other firing in the exact same direction, 30 degrees of axis (maybe). Both passenger and driver would get the same signal strength from each driver. If aimed correctly no eq would be needed. Each would be as loud as the other. Passenger and driver would get the mono and stereo signal without processing. Would that work (mostly)? Maybe to tweeters simplifies the processing needed?


----------



## thehatedguy

I remember back in 1990 putting tweeters on the rear view mirror facing the glass.

This old Eclipse DDL system has a center channel setup that attaches to the review mirror with the speakers pointing foward. There is a processor too, but I'm not sure what kind of logarithm they are using to derive center.


----------



## MarkZ

mitchyz250f said:


> Patrick, what I was suggesting was let’s say you have two tweeters in the center of the dash firing up the windshield or located at the top of the windshield. Left and right tweeter right next to each other firing in the exact same direction, 30 degrees of axis (maybe). Both passenger and driver would get the same signal strength from each driver. If aimed correctly no eq would be needed. Each would be as loud as the other. Passenger and driver would get the mono and stereo signal without processing. Would that work (mostly)? Maybe to tweeters simplifies the processing needed?


What you're describing, if I understand it, is a simple summing. Processors can do the same thing pretty easily through one tweeter. Hell, you don't really need a processor to pull that off, actually.


----------



## mitchyz250f

I think MarkZ and thehatedguy are talking about three tweeters. Left, right and center with processing. Patrick is talking about one tweeter in the middle with processing (I think). I am talking about using what everyone has right now, but just moving the location of the tweeters to the middle of the dash firing up along the window. No processing. 

I going to stop now, I feel like the dumb kid in class that is the only one that didn't get the homework assignment right.


----------



## fury

For a single tweeter in the middle of the car, you would require a summed mono signal no...?
Otherwise you could potentially be losing information from the original stereo recording.

For a three tweeter system (L/C/R) i'd suggest processing would be required.


----------



## Patrick Bateman

mitchyz250f said:


> I think MarkZ and thehatedguy are talking about three tweeters. Left, right and center with processing. Patrick is talking about one tweeter in the middle with processing (I think). I am talking about using what everyone has right now, but just moving the location of the tweeters to the middle of the dash firing up along the window. No processing.
> 
> I going to stop now, I feel like the dumb kid in class that is the only one that didn't get the homework assignment right.


Ha! I feel like the dumb kid. I gave it a try today. Best soundstage I've ever heard in a car.

Anyone want to buy some Unity horns?


----------



## CraigE

Patrick Bateman said:


> Ha! I feel like the dumb kid. I gave it a try today. Best soundstage I've ever heard in a car.
> 
> Anyone want to buy some Unity horns?


:snacks: Okay.... we're waiting for pix and analysis.


----------



## Se7en

X2! Which config did you actually try? Single tweet summed, no other tweets playing in the car? Or multiples?


----------



## dlechner

Patrick Bateman said:


> Ha! I feel like the dumb kid. I gave it a try today. Best soundstage I've ever heard in a car.
> 
> Anyone want to buy some Unity horns?


This is funny. Ever since Patrick started this thread, I have been playing with some of these ideas. I thought my ears were decieving me when I placed both of the tweeters in the center of the dash firing up. I can't remember which orientation gave me the best results, but the results were surprising to say the least. I was even more surprised when I switched the passenger side tweeter to driver and visa versa.


----------



## Patrick Bateman

Se7en said:


> X2! Which config did you actually try? Single tweet summed, no other tweets playing in the car? Or multiples?


I threw together a variation of what JL audio did in their new show car. There are two tweeters in the center of the dash, and an eight inch woofer in a sealed box each kick panel.

Basically I was inspired by a couple of things:








JL is using a wide spacing on their tweeters, and I was trying to figure out why they were doing this. A properly spaced array creates a "forward lobe" where the two speakers sum, focusing their energy into a beam. The thing is, the spacing on the JL speakers is wrong. So I was trying to figure out what they were up to. The pic above is for radar, but it's the same idea. Works with light, sonar, radar, sound, etc...
I bought an RFQ5000 on Ebay, paid for it, and then the seller emailed me that he was out-of-stock. LAME. So I won't be doing a five channel set up.

I took some pics, listened to it for a few hours, but haven't measured it yet. I'll post some impressions later.


----------



## Se7en

So, were to tweeters recieiving a summed mono signal, appropriate L/R or reversed L/R?

Also, were you just firing directly forward (off axis to the listening position) or on axis.

I'm assumiing that these were the only tweeters playing in the car.

Thanks a bunch!


----------



## 94VG30DE

Patrick Bateman said:


> I threw together a variation of what JL audio did in their new show car. There are two tweeters in the center of the dash, and an eight inch woofer in a sealed box each kick panel.
> 
> Basically I was inspired by a couple of things:
> 
> 
> 
> 
> 
> 
> 
> 
> JL is using a wide spacing on their tweeters, and I was trying to figure out why they were doing this. A properly spaced array creates a "forward lobe" where the two speakers sum, focusing their energy into a beam. The thing is, the spacing on the JL speakers is wrong. So I was trying to figure out what they were up to. The pic above is for radar, but it's the same idea. Works with light, sonar, radar, sound, etc...
> I bought an RFQ5000 on Ebay, paid for it, and then the seller emailed me that he was out-of-stock. LAME. So I won't be doing a five channel set up.
> 
> I took some pics, listened to it for a few hours, but haven't measured it yet. I'll post some impressions later.


So the overlap ("lobe") where the two tweeters sum is designed to keep the image planted strongly in the center, while the normal off-axis FR takes care of the rest of the width? My plan was to just toss my tweeters in small spherical enclosures and start moving them around the dash to see what they do, but it sounds like some of you guys beat me to it.


----------



## Fast1one

Patrick Bateman said:


> I threw together a variation of what JL audio did in their new show car. There are two tweeters in the center of the dash, and an eight inch woofer in a sealed box each kick panel.
> 
> Basically I was inspired by a couple of things:
> 
> 
> 
> JL is using a wide spacing on their tweeters, and I was trying to figure out why they were doing this. A properly spaced array creates a "forward lobe" where the two speakers sum, focusing their energy into a beam. The thing is, the spacing on the JL speakers is wrong. So I was trying to figure out what they were up to. The pic above is for radar, but it's the same idea. Works with light, sonar, radar, sound, etc...
> *I bought an RFQ5000 on Ebay, paid for it, and then the seller emailed me that he was out-of-stock. LAME. So I won't be doing a five channel set up.*
> 
> I took some pics, listened to it for a few hours, but haven't measured it yet. I'll post some impressions later.


That's unfortunate. Mine shipped out yesterday


----------



## Patrick Bateman

Se7en said:


> So, were to tweeters recieiving a summed mono signal, appropriate L/R or reversed L/R?
> 
> Also, were you just firing directly forward (off axis to the listening position) or on axis.
> 
> I'm assumiing that these were the only tweeters playing in the car.
> 
> Thanks a bunch!


Nothing fancy. A pair of tweeters set up like JL set them up, each receiving a conventional unmanipulated signal. Based on my understanding of Blauerts book, interaural time delay is virtually inaudible above 1600hz. I highpassed the tweeters at 3khz to be safe.

Since I'm OCD when it comes to directivity, i used a shallow waveguide on the tweeters and a specific spacing that would create a "forward lobe." The forward lobe attenuates off-axis energy by about 6dB. That doesn't sound like a lot, but it's the equivalent of cutting the power by 75%! The idea is to eliminate reflections off the side windows.

The tweeters are firing forward, but the array and the waveguide are controlling the directivity more than aiming will.

It doesn't take much of a waveguide to control directivity at high frequencies - a 4.5" waveguide will control directivity down to 3khz.

Anyways, the results were completely mind-bending. With my Unity horns I was able to create a soundstage that exceeded the boundaries of the car to a slight degree. With this configuration, I would occasionally hear songs that exceeded the width of the car to a great degree. But the interesting part was that the width of the stage was greatly influenced by the recording. For instance, mono podcasts had an image the size of a basketball, while recordings with lots of reverb had a soundstage that was about ten feet wide.

I've never heard a car that could do this. As we speak I'm copying over a bunch of reference tracks, to see if my perception was a fluke. I'll be doing some measurements when I get a chance.


----------



## BigRed

pics man....pics


----------



## mitchyz250f

Yeah, which one did you try.


----------



## MarkZ

Se7en said:


> So, were to tweeters recieiving a summed mono signal, appropriate L/R or reversed L/R?


My point earlier was that these three options are the same. Summing in the acoustical domain is (pretty much) the same as summing in the electrical domain.

[The above assumes that the tweeters are close enough together, relative to the distance from the listener, to behave like a point source.]


----------



## Patrick Bateman

mitchyz250f said:


> Yeah, which one did you try.


I have a bunch of drivers at my disposal, but the key to this is to create a REALLY strong forward lobe.

For instance, JL is using a 1" tweeter, and due to the small diaphragm, the two drivers are going to interfere with each other in a huge way. I simulated them using the tools from FRD Consortium, and the two tweeters suffer from a ton of constructive and destructive interference.

If you use a larger diaphragm, a waveguide, or both, you can prevent them from interfering with each other for the most part.

It's the same idea as that pic I posted this morning - you get a beam right down the center of the car, and each person is listening to the same beam off-axis.
















​
The woofers in the kick panels are B&C 8NDL51 in sealed boxes, the same ones from my 2001 Accord project on audiogroupforum. The tweeters are Peerless 2" woofers. I guess that isn't a "tweeter" per se, but they have output to 20khz and narrower directivity than a 1" diaphragm.

(And we WANT narrow directivity, to get the windows out of the mix.)


----------



## dcm220

Apparently, there were THREE sets of tweeters in that GTI. Here's what JL audio has to say about those tweeters:

"Each of the front doors is occupied by a pair of JL Audio XR650-CW, 6.5-inch component woofers mounted side-by-side with an XR100-CT tweeter mounted just above and between them. This satellite system is a derivation of an array technique JL Audio has used in most of its show cars over the past few years. A second XR100-CT tweeter for each channel is mounted on a custom aluminum "tweeter bridge bar" located on the top of the dash. The fabricators managed to keep the path length of the dash tweeter and door tweeter identical for the listener on that side of the car. A third XR100-CT tweeter for each channel is mounted in the factory tweeter location in the outside mirror triangle of each door. This tweeter is crossed over above 15KHz and does not contribute heavily to the overall sound... it is said to simply add a bit of width and "air" to the soundstage."



Patrick Bateman said:


> I threw together a variation of what JL audio did in their new show car. There are two tweeters in the center of the dash, and an eight inch woofer in a sealed box each kick panel.
> 
> Basically I was inspired by a couple of things:
> 
> 
> 
> 
> 
> 
> 
> 
> JL is using a wide spacing on their tweeters, and I was trying to figure out why they were doing this. A properly spaced array creates a "forward lobe" where the two speakers sum, focusing their energy into a beam. The thing is, the spacing on the JL speakers is wrong. So I was trying to figure out what they were up to. The pic above is for radar, but it's the same idea. Works with light, sonar, radar, sound, etc...
> I bought an RFQ5000 on Ebay, paid for it, and then the seller emailed me that he was out-of-stock. LAME. So I won't be doing a five channel set up.
> 
> I took some pics, listened to it for a few hours, but haven't measured it yet. I'll post some impressions later.


----------



## mitchyz250f

If the speakers are in the center of the dash, is it really that critical is to eliminate reflections? Is the distance great enough that our brains will seperate them as reflections?

If you were to cross at 3000hz and had the tweeters less than 3" apart (center to center), wouldn't they 'sum' and beam like a single speaker? The advantages of using tweeeters would be;
-better highs cause they are tweeters
-smaller and more stealthy
-I already own tweeters


----------



## lycan

Patrick Bateman said:


> Nothing fancy. A pair of tweeters set up like JL set them up, each receiving a conventional unmanipulated signal. Based on my understanding of Blauerts book, interaural time delay is virtually inaudible above 1600hz.


Here's why : it's all about the distance between our ears.

At longer wavelengths, there's just NOT going to be much amplitude difference between our ears (for a source located substantially farther away than the distance between our ears). The head plays no role in diffraction at these long wavelengths. BUT the ear/brain has learned to localize these long wavelengths by measuring the arrival _time_ difference ... which we can interpret to mean "time between peaks", for example, in the pressure wave.

At short wavelengths ... comparable to, or shorter than, the distance between our ears ... such "timing" information is very confusing to the ear/brain. If there's two or three "pressure peaks" in the span between our ears, arrival TIME information is confusing at best! However, head shadowing starts to play a VERY important role (not coincidentally, at wavelengths comparable to the dimensions of our heads), which contributes to INTENSITY differences between our ears at shorter wavelengths.

In other words : nothing "magical" about 1600Hz, in the sense that we need to accept a guru's word for it ... it just corresponds to acoustic wavelengths that approximately match the span between our ears


----------



## Patrick Bateman

These are good questions.




mitchyz250f said:


> If the speakers are in the center of the dash, is it really that critical is to eliminate reflections? Is the distance great enough that our brains will seperate them as reflections?


If I understand you correctly, you're asking if reflections off the side windows are a big deal, since the tweeters are about 42" from each. It's going to take 3.1 milliseconds to hit the side window. According to the research, anything *after* 10-20 milliseconds improves ambience.

So, yes, we want to get rid of those side reflections. It is my belief that reflections are more obnoxious as we get closer to 0ms, but I haven't seen any studies to back that up.

The JL solution doesn't attenuate side reflections, but they're still delayed in time due to distance.



mitchyz250f said:


> If you were to cross at 3000hz and had the tweeters less than 3" apart (center to center), wouldn't they 'sum' and beam like a single speaker?


Getting the two speakers to sum is tricky. It isn't as easy as putting them close together, because the wavelengths create constructive and destructive interference. So you end up with peaks at one frequency and nulls at another.

That's the bad news, and the main issue that I could see with the JL implementation. It doesn't appear that they did anything to deal with that, and the comb filtering looks really obnoxious on paper. Then again, I tried a few different spacings, and the spacing used by JL *does* look good. So it *does* appear that they tried different widths.

Basically, the JL probably suffers from comb filtering, but the spacing that they used spreads it out. There aren't any huge peaks or nulls.

I wish I had some measurements of mine. It was designed to use a waveguide to control directivity down to about 4000hz. By using a waveguide, you minimize interaction between the two drivers.







Here is an array of Unity horns. It's the same idea. They approximate one big speaker. You can't do this with direct radiators, or at least not very well. Waveguides solve a lot of array problems IMHO.



mitchyz250f said:


> The advantages of using tweeeters would be;
> -better highs cause they are tweeters
> -smaller and more stealthy
> -I already own tweeters


I don't agree that the highs would be better. Due to the small size of the radiator, the two are going to comb filter each other. You *want* this thing to beam. Beaming is fundamental to eliminating the sound of the car itself. Tweeters have a small diaphragm, and don't start beaming until 14khz or so.

A tweeter in a waveguide *would* work, and I considered it.

One downside to this whole scheme is that it doesn't sound like a car stereo any more, it sounds like a giant pair of headphones now, with a solid center image and the stage is a bit forward.

I wonder if JL added the tweeters to make it sound more "diffuse?"

You could do that with electronics too. (Ambiphonics anyone?)


----------



## lycan

94VG30DE said:


> So the overlap ("lobe") where the two tweeters sum is designed to keep the image planted strongly in the center, while the normal off-axis FR takes care of the rest of the width? My plan was to just toss my tweeters in small spherical enclosures and start moving them around the dash to see what they do, but it sounds like some of you guys beat me to it.


Don't confuse where the primary tweet _energy_ is directed, with where the apparent _image_ will be 

When Patrick et al are discussing the virtues of aiming/waveguides/arrays to direct primary tweet radiation to the CENTER of the car ... both to minimize reflections, and to exploit off-axis attenuation to combat side bias ... this does NOT mean that the CENTER image will be emphasized above all else.

Quite the opposite, actually


----------



## 94VG30DE

lycan said:


> Don't confuse where the primary tweet _energy_ is directed, with where the apparent _image_ will be
> 
> When Patrick et al are discussing the virtues of aiming/waveguides/arrays to direct primary tweet radiation to the CENTER of the car ... both to minimize reflections, and to exploit off-axis attenuation to combat side bias ... this does NOT mean that the CENTER image will be emphasized above all else.
> 
> Quite the opposite, actually


Gotcha. That makes more sense. And also sounds better I would guess . Haha thanks for letting the special ed kids talk in class. Still learning


----------



## Patrick Bateman

I listened to some tracks in the car, using this setup, with ambiophonics. If anyone is playing along at home, here's how you can repeat the experiment.

#1 - get foobar2000
#2 - Configure the convolver for ambiophonics. I think the files are here, google is your friend: Ambiophonics - An experiment and a How to using foobar2000. - Page 2 - MP3Car.com
#3 - Output the files as wavs in foobar2000, and load them on your music player of choice

Because extra channels aren't required, you can do this with any media player. No carputer required.


----------



## Fast1one

Patrick Bateman said:


> One downside to this whole scheme is that it doesn't sound like a car stereo any more, it sounds like a giant pair of headphones now, with a solid center image and the stage is a bit forward.
> 
> I wonder if JL added the tweeters to make it sound more "diffuse?"
> 
> You could do that with electronics too. (Ambiphonics anyone?)


I have a suggestion for that. 

Use electronics (or simply invert a channel) to create a L-R and R-L channel and mount them in the rear. This will carry the ambiance information needed to sound more natural. 

BUT we have a small problem. Interaction with the main tweeters will distract from the image. Solution? Add 10-20ms of delay! If you only have access to 10ms I would suggest acoustically adding more by moving them as far away as possible.

Should be another REALLY easy experiment for you


----------



## Patrick Bateman

lycan said:


> Don't confuse where the primary tweet _energy_ is directed, with where the apparent _image_ will be


Exactly. Reflective surfaces act like a mirror, creating a replica of the original sound, but delayed in time.







In this pic of the speaker on the center of the dash, you can actually *see* the reflection, thanks to the camera's flash.

So reflections are inescapable in this environment. The trick is to delay them as much as possible, or else get them so close to the diaphragm that they "blend" into the initial wave. Or both.



lycan said:


> When Patrick et al are discussing the virtues of aiming/waveguides/arrays to direct primary tweet radiation to the CENTER of the car ... both to minimize reflections, and to exploit off-axis attenuation to combat side bias ... this does NOT mean that the CENTER image will be emphasized above all else.
> 
> Quite the opposite, actually


The nice thing is that it doesn't take a great deal of attenuation or diffusion to improve things. Take a minute to play around with an SPL calculator, and you'll find that attenuating things by even 3dB makes a big improvement, and 6dB is night and day.

So these graphs of directivity are a bit deceptive, because attenuation the off-axis energy even a small amount makes a big difference.


----------



## Patrick Bateman

BigRed said:


> pics man....pics


Here ya go! Took them at night, so they're blurry.







Here it is on my dash. The entire unit is the width of one of my waveguides.

The midranges are the $8 2" woofers from Peerless at Parts Express. These are a nice unit - they have an underhung motor and a copper cap to reduce distortion. Yes, they look like crappy computer speakers but there's more technology in there than you'll find in many speakers that cost $50 each.

The midranges are sunk into a conical waveguide that's 3" wide. That controls directivity horizontally and vertically down to 4500hz. The PVC pipe is used to diffuse energy radiated to the left and to the right, using the same ideas as my spherical loudspeaker thread.

If you model this array using FRD tools you'll see that we get a significant attenuation of off-axis energy over the entire bandwidth. It's basically a refinement of what JL is doing. I don't believe the extra tweeters are necessary, though they will certainly alter the presentation. Whether that's a good thing is uncertain.

If anyone wants to build one of these, it literally took 90 minutes. If that. You just need a drill press, a router, table saw and a 2" hole saw.









Didn't have the proper fasteners 









This thing really isn't very big
​​


----------



## danssoslow

Is the rear being open get a canceling effect beyond the left and right of the baffle, like a dipole? How critical are the center to center dimensions? Could they be widened slightly to keep the center diffuser out of the waveguide?


----------



## MarkZ

Patrick Bateman said:


> Getting the two speakers to sum is tricky. It isn't as easy as putting them close together, because the wavelengths create constructive and destructive interference. So you end up with peaks at one frequency and nulls at another.


Yes, and this problem wanes the closer you can get them to each other, and can be partially remedied by not offsetting them horizontally.

But here's an even better question -- why two speakers and not one? Is it you're trying to harness the lobing? This seems risky, because at such high frequencies it seems like it would be too head-position dependent.


----------



## Patrick Bateman

MarkZ said:


> Yes, and this problem wanes the closer you can get them to each other, and can be partially remedied by not offsetting them horizontally.
> 
> But here's an even better question -- why two speakers and not one? Is it you're trying to harness the lobing? This seems risky, because at such high frequencies it seems like it would be too head-position dependent.


I was curious about the same thing. Since they're so close together, they should be virtually operating as a single driver.

Strangely enough, it's WAY better with two. I tried running it with one, and it sounds like mono.

I'm scratching my head on this one. It doesn't seem logical that two speakers so closely spaced would be producing stereo, but that appears to be the case.

Maybe it's due to the wavelength? 6000hz is a bit over two inches long.


----------



## Patrick Bateman

danssoslow said:


> Is the rear being open get a canceling effect beyond the left and right of the baffle, like a dipole?


Yep. This increases your efficiency by about 6dB, which is equivalent to quadrupling the power. My midbasses have an efficiency of about 95dB, and these tiny little drivers are keeping up just fine. In fact I've considered cutting them by 1-2dB.



danssoslow said:


> How critical are the center to center dimensions?


VERY critical. They determine whether you get a forward lobe directed to the back of the car, or a bunch of destructive comb filtering. It's like taking two light beams and angling so they combine as one. The spacing is important.



danssoslow said:


> Could they be widened slightly to keep the center diffuser out of the waveguide?


The diffuser controls directivity, so I'd be reluctant to remove it.

I recorded some tracks using ambiophonics and I found that it made an audible improvment. For instance, without ambiophonics, the soundstage appears to be centered in front of the driver. With ambiophonics, the soundstage is centered above the middle of the dash, and it's deeper.

The thing that I don't like about ambiophonics is that it makes things sound a bit "lispy" and it hurts your dynamic range. This is because it cancels crosstalk electronically.

The thing is, you can do the same thing with a barrier. So that's what I did. I added a short barrier to the speaker.








Here's a pic of one for the home. Yes, this looks ridiculous.

Subjectively, I noticed that the stage is focused a bit better with the barrier. The difference in soundstaging is fairly subtle, likely because the barrier I'm using is just six inches deep, and the speakers are already very close together.

The *real* difference that I noticed was a HUGE improvement in articulation. This is really important to me - articulation is one of those things that very few speakers can do. Unity horns do it very nicely, and it's one of the things that I really like abou them. I believe unity horns are very articulate because all the sound is radiating from an area the size of a tennis ball.

These speakers, with the divider, are similar in this respect, particularly in the range where it counts (above 2khz.)

I'll post some pics, but it's UGLY


----------



## CraigE

I decided to try a temporary setup with both tweeters (Dynaudio MD 102) in the center. Since the Corvette has a center speaker with the factory Bose System, I had the room.

The tweeters were in the upper door location near the AC vent.








I removed the stock grill and fabbed a temporary baffle from 1/4" MDF, and installed both tweeters firing straight up.








A pic from the front.








The only changes were the TA measurements for both tweeters, and matched the output levels.
Well... I've only had a little time to listen, but I'm impressed.
It's like I was able to move the seat back and down 4 to 6 inches.
Stage width still seems good and the drums seem to be further behind the singer. The drums seemed to crowd the singer before.
The seven drum beats are evenly spaced now. Before the first two were right next to each other.
Hopefully BigRed and Buzzman will have time to listen in the next few days.


----------



## tosca

dcm220 said:


> Apparently, there were THREE sets of tweeters in that GTI. Here's what JL audio has to say about those tweeters:
> 
> "Each of the front doors is occupied by a pair of JL Audio XR650-CW, 6.5-inch component woofers mounted side-by-side with an XR100-CT tweeter mounted just above and between them. This satellite system is a derivation of an array technique JL Audio has used in most of its show cars over the past few years. A second XR100-CT tweeter for each channel is mounted on a custom aluminum "tweeter bridge bar" located on the top of the dash. The fabricators managed to keep the path length of the dash tweeter and door tweeter identical for the listener on that side of the car. A third XR100-CT tweeter for each channel is mounted in the factory tweeter location in the outside mirror triangle of each door. This tweeter is crossed over above 15KHz and does not contribute heavily to the overall sound... it is said to simply add a bit of width and "air" to the soundstage."


Do you know how the dash tweeters were powered? I can't remember if they were fed summed mono, left and right or if the right dash tweeter was connected to the left channel and vice versa. Don't recall much eq/processing being used and it seemed like the main goal of this front stage was to not be overpowered by all the big subs in the back.

After reading all the posts by Lycan and Patrick it should have been an acoustical nightmare, but according to the magazine article it was supposed to sound good.


----------



## mitchyz250f

Patrick, are the PVC tubes between the tweeters needed? How detrimental would it be to just be flat between the two tweeters? Also, do the defraction tubes have to protrude forward from the tweeters? Couldn't you just use simple roundovers on the far outside rather than the PVC shapes. Just trying to understand the minimim size of 'this' configuration. I really don't like large objects in the center of my dash.


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## nitro70044

this sound like a cool idea i want to try it how would i wire this for mono?



Patrick Bateman said:


> Has anyone on the forum tried running a system with a single tweeter, instead of two?
> 
> According to recent psychoacoustics research, _"Popular opinion on the topic of consumer audio systems is that low frequencies are “ hard to localize,” a nd thus can be reproduced by a mono sub woofer in some non-critical location. However, a paper discussing DTS’ technique for encoding surround
> sound (Smyth, 1999) stated that “ experimental evidence suggests that it is difficult to localize mid-to-high frequency signals above about 2.5 kHz” (p. 18). Smyth continues, commenting that when a listener is presented with concurrent low and high frequency information, that high frequencies are relatively unimportant for proper image localization. His statement seemed to oppose what is popularly said about localization, and prompted the preliminary research for this thesis."*_
> 
> Here's my understanding of how this would work in our cars:
> 
> Let's say that you have a woofer and a tweeter in the kick panel of your car. The woofer covers everything below 1khz, and the tweeter covers everything above 1khz. (This is a simplification - bear with me.)
> 
> Below 1khz our perception of the soundstage is dominated by pathlength. Due to this, the depth and the width of the soundstage is largely determined by the location of the woofer. This is counter-intuitive but true, and well documented in numerous texts on psychoacoustics.
> 
> Above 1khz, our perception of the soundstage is dominated by frequency response. Have you ever fiddled with the balance knob on your head unit, and noticed that you can move the highs around, but not the lows? For instance, you can move the knob almost all the way to the right, but you can still tell that your woofers are playing, while the high frequencies are dragged over the passenger side? If you can relate to that, then you experienced this phenomenon. It's easier to "trick" our brains into thinking that high frequencies are coming from somewhere else, because our hearing mechanism is sensitive to frequency response above 1khz.
> 
> Now running a single tweeter seems quite bizarre, and it's certainly unconventional. But there ARE some compelling reasons to do it. Here's some food for thought:
> 
> 
> If your tweeter is in the kick panel, the soundstage will vary on whether there are two people in the car, due to reflections. This is the #1 reason that I personally mount tweeters on the dash.
> If your tweeter is in the A-Pillar the soundstage is skewed towards the driver's side, because it's too close. Increasing the level on the opposite tweeter improves the image, but at the expense of the passenger side.
> The side window in a car creates a really nasty reflection. Mounting a single tweeter in the center avoids the reflection entirely.
> The depth and the width of the soundstage is largely determined by the location of the woofers. Dual tweeters are ideal, but only if their levels are equal. Because we're too close to one, and too far from the other, a single mono tweeter may be the best compromise of all.
> 
> Thoughts?
> 
> On the surface, I recognize that this sounds like crazy talk. And it isn't something that I would recommend for the home, because at home we sit equidistant from the speakers. But in the car it's really worth consideration. Keep in mind, this isn't a true "center channel." The thing that I don't like about center channels is that they make the soundstage narrower and shallower. But keep in mind that width and depth is determined by the woofer location, not the tweeter. That's why we DON'T want low frequencies in the middle.
> 
> * http://mue.music.miami.edu/thesis/robert_hartman/robert_hartman_thesis.pdf(pg 88)


----------



## nitro70044

This sounds like a great idea i want to try it ho would i wire this for proper results?


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## Fast1one

nitro70044 said:


> This sounds like a great idea i want to try it ho would i wire this for proper results?


Just wire it normally. No need for summing electronically from what I can see.


----------



## invinsible

I am having my morel H.ovation woofer little high up in doors and the morel mt22 tweeter are placed on the Apiller 90 off axis. They are running passive as of now. For trying out how they sound on the dash, I made use of the tennis ball, mounted the tweeter on the tennis ball and placed them further down on the center of the dash keeping about 6-7" distance between the two. The other thing I did was swapped the H.ovation xover with the dotech ovation xover as it has xover point of 3200hz at 6db slope. 
Now since they are in passive TA is applied to them keeping the midwoofer distance as its a 2 way setup.
Result was quite noticelable. The stage was more wider, almost giving an an illusion that sitting in a car which has more width, since mine is a hatchback. But the stage appeared little lower as before. I also have the rear fillers on the rear doors which is delayed. I tried listening to some tracks both from the driver and co-driver seat and both had almost the same result surprisingly. But, theres one aspect that I wanted, the stage to be high up but I din't spend much time playing around with it. 
I suppose the best would be when I go active with them. I guess playing passive has its limitations. 

Patrick, is it a good idea to use the sphere for these Morel tweeters. Overall I prefer the spheres as they are less obstrutive with the vision. Overall it was a complete different experience than the usual Apiller install, definitely will be going for it once I go active.


----------



## rockinridgeline

If you moved your crossover point higher I would say that your stage probably dropped because you are playing more upper midrange through your midbass/midrange, which would drop your stage.


----------



## Patrick Bateman

mitchyz250f said:


> Patrick, are the PVC tubes between the tweeters needed? How detrimental would it be to just be flat between the two tweeters? Also, do the defraction tubes have to protrude forward from the tweeters? Couldn't you just use simple roundovers on the far outside rather than the PVC shapes. Just trying to understand the minimim size of 'this' configuration. I really don't like large objects in the center of my dash.


I still need to post some subjective comments. Honestly, I was reluctant to do that, because the difference was so amazing that I thought it might be a fluke. So I didn't want to gush about how great it was, only to realize a few days later that it was a novelty.

Anyways, on to your questions.


*Can you minimize the size?*
Sure. Instead of using 2" midranges use the little Vifa DQ25 tweeters that Zaph likes so much. They're $16 IIRC. Push them ALL the way back into the windshield, so the windshield controls the vertical directivity. No offense to the person that tried this in his Corvette, but locating them six inches forward of the windshield will create a bunch of reflections in the cavity where the windshield meets the dash. Basically, you can't avoid them, so pushing the tweeter ALLLLLLLL the way back "fuses" those reflections with the initial wavefront.
The advantage of the 2" drivers is narrower directivity.
*Can you ditch the PVC pipes?*
Sure. But they improve the image. I personally think that removing the PVC pieces compromises the design in a big way. I listened to the setup for a couple days with a physical divider between the tweeters, and found that it improved intelligibility and brought the stage into focus better. This is because it reduces crosstalk between the two tweeters.
On the downside, the divider shifts the stage to the left, reduces width a little bit, and is ugly as HELL.
I'm a really big proponent of reducing diffraction... I can't stress what an improvement it makes.






Take a look at your own car, and look for ways to create a smooth transition from the cone of the woofer to the car itself. See how the edge of the plywood mates to the edge of the PVC which mates to the dash and the windshield? All of this reduces diffraction and makes an audible improvement.






It's the same idea as a stealth bomber... The shape reduces reflections.

There are other improvements you can make too. The whole idea of the physical barrier in the ambiosonics setup is to prevent crosstalk. I think you can do the same thing with a waveguide that has a narrow beamwidth. Which is just what I'm building.

My waveguide setup has a much lower level of high order modes also, and that also takes a big "edge" off of the sound.


----------



## 94VG30DE

I believe you are referring to this tweeter? Vifa DQ25SC16-04, 1" Titanium Dome Tweeter from Madisound 
$13 apiece + shipping. I believe quite a few people on here have run this tweeter with good results.


----------



## Patrick Bateman

invinsible said:


> I am having my morel H.ovation woofer little high up in doors and the morel mt22 tweeter are placed on the Apiller 90 off axis. They are running passive as of now. For trying out how they sound on the dash, I made use of the tennis ball, mounted the tweeter on the tennis ball and placed them further down on the center of the dash keeping about 6-7" distance between the two. The other thing I did was swapped the H.ovation xover with the dotech ovation xover as it has xover point of 3200hz at 6db slope.
> Now since they are in passive TA is applied to them keeping the midwoofer distance as its a 2 way setup.
> Result was quite noticelable. The stage was more wider, almost giving an an illusion that sitting in a car which has more width, since mine is a hatchback. But the stage appeared little lower as before. I also have the rear fillers on the rear doors which is delayed. I tried listening to some tracks both from the driver and co-driver seat and both had almost the same result surprisingly. But, theres one aspect that I wanted, the stage to be high up but I din't spend much time playing around with it.
> I suppose the best would be when I go active with them. I guess playing passive has its limitations.
> 
> Patrick, is it a good idea to use the sphere for these Morel tweeters. Overall I prefer the spheres as they are less obstrutive with the vision. Overall it was a complete different experience than the usual Apiller install, definitely will be going for it once I go active.


Here's a couple of ideas you might consider.

If you've followed the spherical enclosure thread, you've read how people have heard audible improvements from using a spherical enclosure to control diffraction. The way that it does this is that it "sprays" the reflected sound in every direction. Basically the idea is that reflections are unavoidable, so spray them in every direction, instead of getting a strong reflection at a specific frequency.

The idea of jamming small tweeters back into the windshield is to use the cavity to control your vertical directivity.

Basically, each addresses the same problem, but in a different way.

Here's where things get interesting -

If you've followed these threads, or messed around with these options, you know that our *perception* of depth and width is localized to frequencies below 1600hz. So it might be possible to bring the tweeters *forward* off the windshield. To really do this properly, I would mount the tweeters a few inches *above* the dash.









To keep it from looking ridiculous, I'd mount it on one of those arms they sell for GPS devices.









I know that a bunch of people have complained that this thing looks ridiculous. A spherical enclosure doesn't have to very big at all when you're crossing over at high frequency. For instance, if you're using a crossover point of 3000hz, the enclosure can be 1.43" in diameter! (That corresponds to one wavelength, measured around the perimiter of the sphere.)

Again, this is one of those things you just gotta try. When you're experimenting, keep in mind the variables:

As you push the speakers back to the windshield, the reflections off the glass will get higher and higher in frequency. But you can't avoid 'em, so moving the tweeters back pushes them to a frequency where they're less audible.
As you bring the tweeters forward, the reflections off the glass will get *lower* in frequency. At a certain point most of them will be below your crossover point. On the downside, they'll still confuse your image.
The spacing between the two tweeters is important. Check out the array simulator from FRD tools. The center-to-center spacing controls the width of the beam. There are only certain values that are ideal; a lot of this depends on your crossover frequency.
If you're using a waveguide like I am, the angle of the tweeters is important. If you're using spheres, not as much. At this point I am planning on using a very modest bit of crossfire, about 15-30 degrees, just enough to make the right tweeter "hotter" than the left.



If you have some tiny neodymium tweeters like the Vifa DQ25, put 'em in a sphere. You can get them from Michael's crafts for $1. Get some clay for $5 and smooth off any sharp edges. Then mount them towards the center of the car, a few inches *above* the dash.









If you're comfortable with fabrication, and you like the way this sounds, ditch the GPS arm and build something that looks cool like the guys at JL Audio did.


----------



## Patrick Bateman

94VG30DE said:


> I believe you are referring to this tweeter? Vifa DQ25SC16-04, 1" Titanium Dome Tweeter from Madisound
> $13 apiece + shipping. I believe quite a few people on here have run this tweeter with good results.


Yep. Zaph is using them in all of his kits if I'm not mistaken. I personally prefer the SB Acoustics ring radiator, but it's a tough fit due to the size. There isn't anything as small and as inexpensive as the Vifa that is in it's performance class.

The Vifa is also very nice because we don't need to cross it over lower than 2 or 3khz.


----------



## CraigE

Patrick... No offense taken. 
I appreciate your advise, and will try them closer to the windshield.
Buzzman listened last night and thought it was a good improvement over the upper door locations, with better height and depth. He thought the stage had narrowed a bit though. 
We were thinking of moving them forward and separating them also. I can easily separate them up to about 18", but that may be to much.
I'd welcome your suggestion about the separation. The tweeters are crossed at 3200 hz w/ 12db slope.
Thanks for taking the time to post these great threads.

CraigE (the Corvette Guy)


----------



## Patrick Bateman

94VG30DE said:


> I believe you are referring to this tweeter? Vifa DQ25SC16-04, 1" Titanium Dome Tweeter from Madisound
> $13 apiece + shipping. I believe quite a few people on here have run this tweeter with good results.


The problem with the DQ25 is that it needs a good phase plug to narrow directivity in a huge way.

I took apart one of my compression drivers, and found that it has a lot in common with the DQ25, *except* it has an excellent phase plug. As a bonus it's about 10dB more efficient too.







Here's a pic of the Celestion after I took it apart, along with the waveguide that I'm building for this project, and a Vifa dome for comparison's sake.


Read about it here:

Reducing Waveguide Size - diyAudio


----------



## western47

PB,

What driver are you planning on using for these small WG's?

I like this idea as it seems to be on the order of being less intrusive. This would also make a 3-way system a definite possibility with a midbass in the kick for pathlength and a sub in the trunk.


----------



## SStealth

Patrick, Just an idea which could solve your issue's with space and moving the waveguide as far back into the windscreen as possible.

Mount your waveguide to the driver through the firewall. ie. drill a hole into the firewall the diameter of the thread. Mould the waveguide to meet with windsreen and dash right where they meet, the firewall, so you can use your idea of the dash and windscreen extending the waveguide. then screw the driver into the waveguide through the firewall. This would utilise the windsreen and dash as the waveguide making the actual waveguide you need to fabricate quite small. It would mainly involve coupling the throat with the windscreen/dash, and maybe creating a roundover at the sides to reduce difraction, which I know you love doing.

This idea is mainly for mounting the tweeters together in the centre of the dash as I dont think you would have any room for the drivers at the edges of the firewall in the engine bay.

Ant


----------



## mitchyz250f

Patrick - Would using a horn dome tweeter provide any benefit in this application over conventional dome tweeters or possibly the 2" speakers you mention? 

Beyma T2030 - Beyma T2030 metal dome tweeter. Beyma speaker components available at US Speaker.
http://www.madisound.com/catalog/PDF/h1499.pdf
Morel CAT378 Morel Horn Tweeter from Madisound


----------



## Martin

Hi Patrick,

I tried your suggestions yesterday, with - as predicted - excellent results! 

But I encountered one problem. It seems there is some sort of "hole" in staging between mid dashboard and the left side.

I use 6,5" mids in stock locations in the door and 1" tweeters on the dash, as far without waveguides. The tweeters are about 5" apart, mounted directly under the front window and angled to the back of the car.

Is it possible my problem arises because of the missing waveguides? Or through the lack of mid frequencies due to the far more off-axis-position of the left side mid?

Do you have any pictures of your 8" in the kicks? At which position are they angled?

I would greatly appreciate if you could give me any hints regarding that matter.

Thanks for your great threads, Patrick. I hope you keep going on that way!

Greet


----------



## Patrick Bateman

Martin said:


> Hi Patrick,
> 
> I tried your suggestions yesterday, with - as predicted - excellent results!
> 
> But I encountered one problem. It seems there is some sort of "hole" in staging between mid dashboard and the left side.


I am going to post some measurements of the Peerless 830970 woofers that I am using. I finished the measurements last night. Had to build a jig for this one, because it's a tricky measurements. They'll be posted over on diyaudio.com.

Anyways, the reason I wanted to measure the midranges was to figure out why this is working so well.

Here's my hypothesis -

We all know the windows in the front of the vehicle are a problem, but I don't think I realized how BIG of a problem they are. Basically, I'm starting to believe that a lot of the "width" that we hear in stereo recordings in the car is due to reflections off the side glass.

These reflections create a pleasant sense of ambience, but it's not even in the original recording; the windows are basically adding this layer of fog over everything we listen to.

For instance, I've found that the width of recordings varies dramatically with this setup. I've listened to well recorded orchestral pieces where the width of the stage exceeded the car, and I've listened to poorly recorded rock and roll tracks where the width was barely a foot wide.

Basically, the stage *is* narrower than with a conventional set up, but the width varies dramatically. This reminds me a bit of headphones, where it's easier to perceive variations in the quality of the mix.

It takes a bit of getting used to, admittedly.



Martin said:


> I use 6,5" mids in stock locations in the door and 1" tweeters on the dash, as far without waveguides. The tweeters are about 5" apart, mounted directly under the front window and angled to the back of the car.
> 
> Is it possible my problem arises because of the missing waveguides? Or through the lack of mid frequencies due to the far more off-axis-position of the left side mid?
> 
> Do you have any pictures of your 8" in the kicks? At which position are they angled?
> 
> I would greatly appreciate if you could give me any hints regarding that matter.
> 
> Thanks for your great threads, Patrick. I hope you keep going on that way!
> 
> Greet


My midbasses are the same ones from my 2001 Accord. There are pics in the natural bass thread. They're a simple sealed box.

As for angling them, it's completely unnecessary - they don't beam until 1.8khz. With a seven inch driver you won't get beaming until 2500hz, so angling them is unnecessary. (This assumed you use a steep crossover, and it's within an octave of 2500hz. If you're running a shallow crossover, then you *will* hear a difference.)

As for the waveguides, YES, I *do* think that's the key to this whole thing. That's why I spent most of my Saturday doing measurements on the Peerless. I believe that what's happening is that the Peerless has a much narrower beamwidth than a conventional tweeter, and due to that, it's reducing reflections off the dash, roof, and windows.









Here's the polar response of a compression driver and a waveguide. See how it decays smoothly as you fall off axis? The measurements that I did last night show that the 830970 in a very small waveguide exhibits similar behavior. That's why it has a beam that's focused straight down the middle of the cabin.








Here's the polar response of a "stock" one-inch tweeter, with no waveguide. See how the off-axis response isn't nearly as nice?​
This is likely a big part of the reason I am getting good results with this. If you do the same thing with a conventional tweeter, you're going to have a much larger beam, due to the smaller size of the diaphragm.

The Peerless has a diaphragm that's twice the size of a conventional tweeter AND I have it in a very small waveguide. Combine these two things, and you have directivity control all the way down to 3khz. 

If everything goes according to plan, I will be demonstrating a device that combines the excellent off-axis response of the waveguide above, but in a much smaller footprint, in the next few days. I'm building it as we speak.


----------



## Patrick Bateman

mitchyz250f said:


> Patrick - Would using a horn dome tweeter provide any benefit in this application over conventional dome tweeters or possibly the 2" speakers you mention?
> 
> Beyma T2030 - Beyma T2030 metal dome tweeter. Beyma speaker components available at US Speaker.
> http://www.madisound.com/catalog/PDF/h1499.pdf
> Morel CAT378 Morel Horn Tweeter from Madisound


A horn tweeter will work better than a dome, but what you really want is a waveguide. They're not difficult to build - the one that I'm building now took all of 90 minutes to make.

On the downside, you need a router, a drill press, and about $100 worth of hole saws and bits.

Last night a member posted some pics of a waveguide he built by hacking up a Dayton waveguide, and it looks 10x better than anything I've made. Definitely worth a look.

http://www.diymobileaudio.com/forum/diyma-build-logs/13527-dodge-ram-install-thread-new-post.html


----------



## Niebur3

Patrick Bateman said:


> A horn tweeter will work better than a dome, but what you really want is a waveguide. They're not difficult to build - the one that I'm building now took all of 90 minutes to make.
> 
> On the downside, you need a router, a drill press, and about $100 worth of hole saws and bits.
> 
> Last night a member posted some pics of a waveguide he built by hacking up a Dayton waveguide, and it looks 10x better than anything I've made. Definitely worth a look.
> 
> http://www.diymobileaudio.com/forum/diyma-build-logs/13527-dodge-ram-install-thread-new-post.html


Patrick, I have a few questions regarding this setup. 

Do the tweeters need to be facing you (like the JL example) or can they be mounted in the dash so they fire up at the windshield as long as they are mounted as deep as the JL or even deeper? 

Do you know the difference in sound between these two mounting options or have any assumptions about the difference? 

Where would be the best place to mount the mids (3-4" midrange) if you use tweeters for this setup (can they still be on the dash/a-pillar or would you want to go with the kicks or doors)?

Is a steep windshield (corvette, firebird, other sports cars) cause a horn effect without actually using a horn?

Thanks...this thread is awesome!!!


----------



## ryan s

How would we determine the size of the waveguide? Is there some kind of formula? Just blend them into the windshield/dash?

I'm considering putting my 3" "tweeterless mids" in the center, at least to try. Would their directionality be too "narrow" to use in the center?


----------



## Patrick Bateman

Niebur3 said:


> Patrick, I have a few questions regarding this setup.
> 
> Do the tweeters need to be facing you (like the JL example) or can they be mounted in the dash so they fire up at the windshield as long as they are mounted as deep as the JL or even deeper?


_All of these answers are based on my understanding of psychacoustics. But some things work better than others, so I invite you to mess around with this.

Having said that..._ 

I would personally use some kind of a waveguide and fire the tweeters so that the beam is as far from the dash and the ceiling as possible. In my car this means they're aimed up a bit.

*Do not fire them straight up at the windshield* - that will create a peak and a null in the frequency response. You can calculate the peak and the null; the former is at 1/2 wavelength and the latter is at 1/4 wavelength.

You might be able to get away with firing them up if you get them very VERY close to the windshield, like within a half inch. The stock locations in my car do exactly that.



Niebur3 said:


> Do you know the difference in sound between these two mounting options or have any assumptions about the difference?


Sure. This whole thing basically depends on getting the reflections off the windshield, the side windows, the dash and the roof. If aim it up at the window you'll get a strong reflection off the windshield, and if you don't, you won't.



Niebur3 said:


> Where would be the best place to mount the mids (3-4" midrange) if you use tweeters for this setup (can they still be on the dash/a-pillar or would you want to go with the kicks or doors)?


That depends on your crossover. We're sensitive to height above 1600hz or so. Ideally I'd put a midrange in each corner, covering the midrange only, with a crossover that's at 3khz or higher. Probably cover two octaves, from 750 to 3000hz. In this scheme the midranges are somewhere around the A-Pillar, tweets are in the center like JL did, and the midbasses are likely in the kick panels, or even the doors.

If a three way is too much work, I'd probably do what I'm doing now - big beefy midbasses in the kick panels, running them all the way up to 3khz or so.



Niebur3 said:


> Is a steep windshield (corvette, firebird, other sports cars) cause a horn effect without actually using a horn?
> 
> Thanks...this thread is awesome!!!


This last part is really REALLY important. You DON'T need much of a waveguide here. I did some measurements last night, and I am going to post them soon. I was able to get full control of directivity down to the crossover point with a waveguide that's just 3/4" deep. I mean seriously, that's next to nothing. These frequencies are very short, it doesn't take a lot to control directivity up high.







Just ask JBL...


----------



## Patrick Bateman

ryan s said:


> How would we determine the size of the waveguide? Is there some kind of formula? Just blend them into the windshield/dash?
> 
> I'm considering putting my 3" "tweeterless mids" in the center, at least to try. Would their directionality be too "narrow" to use in the center?


Basically make the dimensions of the mouth equal to the crossover frequency. So with a crossover frequency of 3000hz, the mouth is 4.5" across.*

That's it!

Simple huh?

The depth of the waveguide will depend on how wide you want the coverage to be, and how big your radiator is. The reason that the Peerless can use a waveguide that's just 3/4" deep is that the radiator is so big to begin with. If it was a 1" dome the depth would be deeper.

* sound travels at a speed of 13500 inches per second.


----------



## ryan s

Patrick Bateman said:


> Basically make the dimensions of the mouth equal to the crossover frequency. So with a crossover frequency of 3000hz, the mouth is 4.5" across.*
> 
> That's it!
> 
> Simple huh?
> 
> The depth of the waveguide will depend on how wide you want the coverage to be, and how big your radiator is. The reason that the Peerless can use a waveguide that's just 3/4" deep is that the radiator is so big to begin with. If it was a 1" dome the depth would be deeper.
> 
> * sound travels at a speed of 13500 inches per second.


What about with a lower XO frequency? I was planning on crossing these (Tang Band Bamboos) around 500Hz. That means a waveguide of 27" :surprised: I hate math so that's probably wrong :laugh:

As an aside, but related to the discussion seeing that JBL speaker...

I listened to my Klipsch Promedia 2.1 set fairly critically for the past 2 days, roughly on axis.

The sound was planted squarely in front of me...I mean it sounded like the computer screen was playing the music.

And the reason why I think they sound so good (for computer speakers) is their...drumroll...waveguide design:









I had never thought about it until I started reading these threads...


----------



## lycan

Patrick Bateman said:


> We're sensitive to height above 1600hz or so. Ideally I'd put a midrange in each corner, covering the midrange only, with a crossover that's at 3khz or higher. Probably cover two octaves, from 750 to 3000hz. In this scheme the midranges are somewhere around the A-Pillar, tweets are in the center like JL did, and the midbasses are likely in the kick panels, or even the doors.


a correction, if i may :

1600Hz is the approximate frequency where we transition from ITD (inter-aural time difference) location cues to IID (inter-aural intensity difference) location cues ... in the LATERAL plane. That frequency comes from the wavelength corresponding to the distance between our ears (about 8 inches), which of course is about the width of our head. Below this frequency, there is no head shadowing or other diffractive effects to cause a difference in amplitude for the signal at each ear ... so arrival _time_ rules. Above this frequency, time or phase cues become ambiguous as more than 1 wavelength "fits" between our ears ... so _intensity_ rules.

In the vertical plane, the important dimension to consider is _not_ the distance between our ears (that's an orthogonal dimension). Instead, the important dimension is the _size_ of our outer ears ... maybe, about 4 inches. It's the outer ear ... and _only_ the outer ear ... shape that spoils the _vertical_ symmetry of our heads, allowing us to localize vertically.

Bottom line : we start to localize vertically about an octave higher than 1600Hz 

Might sound like i'm nit-picking, but when you're trying to fit drivers on the dash, a factor-of-two can be significant!


----------



## mitchyz250f

Mr. Lycan and Patrick, from what I can see this is what we are saying, assuming we have TA available;

Sub –defined as 80 Hz and lower. Can go anywhere.
Not sure if path length is critical.

Midbass - defined as 80 to 320/640 Hz, 
Effects - stage width.
Critical – as far to the side as possible so that our brains see the greatest shadowing based on our head size. Question – wouldn’t the greatest shadowing take place directly on axis with/through our ears?
Not critical - is path length
Suitable locations – doors, kicks anywhere as far left and right as possible.

Midrange –defined as 320/640ish to 3200ish (wolves have big ears, my ears are only 3” long), 
Effects – stage depth
Critical - long path lengths. 
Not critical – driver height
Suitable locations - kicks and doors


Tweeters – defined as 3200ish and above. Good locations are pillars and dash. Location
Effects – stage height
Critical – Height of drivers and sound pressure differences between left and right tweeters
Not critical – Path Length and TA
Suitable locations – classically pillars and dash. However advanced development underway at DIYMA.com.

I wrote this so that it could be corrected, and to collate all the information in one place. So please correct any misinformation presented.


----------



## lycan

no shadowing in the midbass. In the midbass, it's all ITD. The ear can ONLY tell the arrival time differences. Strictly a function of distance between the ears ... nothing more.

ANY points in space that generate the same ITD's will be indistinguishable.

I've called this geometry a "circle of confusion" ... which is true, to an extent 

Who's interested in a homework assignment?

Let's start in 2-D  Say the distance between the ears is *e*. Imagine an x-y coordinate system, where the left ear is located at *(-e/2, 0)* and the right ear is located at *(e/2, 0)*. With me so far? Don't want to hijack ... who's game?


----------



## Fast1one

lycan said:


> no shadowing in the midbass. In the midbass, it's all ITD. The ear can ONLY tell the arrival time differences. Strictly a function of distance between the ears ... nothing more.
> 
> ANY points in space that generate the same ITD's will be indistinguishable.
> 
> I've called this geometry a "circle of confusion" ... which is true, to an extent
> 
> Who's interested in a homework assignment?
> 
> Let's start in 2-D  Say the distance between the ears is *e*. Imagine an x-y coordinate system, where the left ear is located at *(-e/2, 0)* and the right ear is located at *(e/2, 0)*. With me so far? Don't want to hijack ... who's game?


I had my suspicions, but it wasn't until this post that I increased my level of investigation. Welcome sir, it is truly an honor to have you posting at our little niche haven 

And I am not interested in a homework assignment, at least not another. Already swamped with enough as it is 

I really want to try this with someone's car. There is too much revolution going on in mine, lol.


----------



## 94VG30DE

lycan said:


> no shadowing in the midbass. In the midbass, it's all ITD. The ear can ONLY tell the arrival time differences. Strictly a function of distance between the ears ... nothing more.
> 
> ANY points in space that generate the same ITD's will be indistinguishable.
> 
> I've called this geometry a "circle of confusion" ... which is true, to an extent
> 
> Who's interested in a homework assignment?
> 
> Let's start in 2-D  Say the distance between the ears is *e*. Imagine an x-y coordinate system, where the left ear is located at *(-e/2, 0)* and the right ear is located at *(e/2, 0)*. With me so far? Don't want to hijack ... who's game?


I think I'm game for a Cartesian coordinate explanation of what we are talking about. Could help a lot of people out to have something visual (and grid/math based).


----------



## Fast1one

94VG30DE said:


> I think I'm game for a Cartesian coordinate explanation of what we are talking about. Could help a lot of people out to have something visual (and grid/math based).


I think vector notation would be even better, but we may loose some of the non-engineering types


----------



## lycan

lycan said:


> no shadowing in the midbass. In the midbass, it's all ITD. The ear can ONLY tell the arrival time differences. Strictly a function of distance between the ears ... nothing more.
> 
> ANY points in space that generate the same ITD's will be indistinguishable.
> 
> I've called this geometry a "circle of confusion" ... which is true, to an extent
> 
> Who's interested in a homework assignment?
> 
> Let's start in 2-D  Say the distance between the ears is *e*. Imagine an x-y coordinate system, where the left ear is located at *(-e/2, 0)* and the right ear is located at *(e/2, 0)*. With me so far? Don't want to hijack ... who's game?


Hijack won't last too long ... promise 

Pick a point in the upper right quadrant, call it *(x,y)* (i'm clever that way) This "point" is the location of a sound source ... and this "point" has a _distance_ to the left ear, and a _distance_ to the right ear. The DIFFERENCE between these two distances is representative of the inter-aural time delay  Are you with me?

Let's define this DIFFERENCE as *d*. Now here's the assignment :

1. Write down the expression for *d*, as the difference of two distances.
2. Re-arrange the expression (this takes some algebra) to reveal the famous "curve" that describes all points in 2-D that have the same inter-aural time delay (represented in our assignment as *d*). Hint : it's a classic conic section.


----------



## Blake Rateliff

Please tell me if I've drawn the right conclusion on this.

Patrick described in another thread that, for midrange/midbass, you can trick the brain into thinking arrival times are more similar than they actually are by increasing the amplitude of the speaker that is farthest from the listener.

This doing this electronically would only resolve the problem for one listener though.

So the solution would be to use the directivity of a waveguide to attenuate the sound for the speaker that the listener is nearest. If distance between the speaker nearest the listener and the speaker farthest from the listener are the same for each side, and the directivity is the same on each side but inverted, then you can achieve a coherent stage for the midrange and midbass in both seats.


----------



## sqshoestring

To the OP, I just don't think I could bring myself to a center speaker of any kind other than a sub. I'm so bad about stereo I run rears to purposely pull the stage back to me, then I get a great left channel and wide stage. It might mess up other things, but I have a left channel outside the window all the time. Then again I've always liked the sound of headphones the best for imaging, better than any speaker arrangement in a house. Some say music is not mixed/produced for headphone separation, but I don't care.


----------



## martinkruit

Nice tread.

I was using a center speaker on my dash.

I will try a tweeter instead. 
(disconnecting my tweeters in the a pillars)


----------



## mosconiac

PB: I'm assuming you mounted your tweeters side-by-side for more than aesthetic purposes. Would you agree that your configuration of a pair of tweeters is somewhat of a d'Appolito scheme? Using this typically midrange-exclusive feature controls dispersion on one axis, the horizontal in your case (vertical in the classic configuration). Therefore, vertical dispersion (to the dash & to the windshield) is unaffected, yet horizontal dispersion (side windows) is narrowed. Could this be why you like it so much...less reflections off the side windows as opposed to direct-radiated sound?

You've commented that you/we should tuck the tweeters into the windshield & dash to keep reflections off those surfaces nearly time-aligned with the direct-radiated sound. Therefore, controlling dispersion in that direction is not as critical.


----------



## jimbno1

I am really digging this thread. Any updates? Anyone besides Corvette and Patrick try this and have any progress reports?


----------



## sqshoestring

Yes let us know how it works, it just seems a little out there. Hey my first cars had a single dash speaker, I kind of remember it, until I hacked holes in the doors.


----------



## 94VG30DE

I was planning on trying it when I do some revisions on my front stage (was already looking for new locations for my tweeters), but that won't be for probably another month


----------



## Patrick Bateman

mosconiac said:


> PB: I'm assuming you mounted your tweeters side-by-side for more than aesthetic purposes. Would you agree that your configuration of a pair of tweeters is somewhat of a d'Appolito scheme?


A D'Appolito array does a crude approximation of a point source using two woofers and a tweeter. The center to center spacing of the woofers will create a forward lobe, reducing reflections off the floor and ceiling.

I think there are some problems with the D'Appolito array, but there's a nice alternative that nobody uses. I wrote a monster of a post about it here:

D'Appolito Arrays with Waveguides - diyAudio

(Put it on Diyaudio because I don't think anyone is loony enough to put a 200lb array in their car  )



mosconiac said:


> Using this typically midrange-exclusive feature controls dispersion on one axis, the horizontal in your case (vertical in the classic configuration). Therefore, vertical dispersion (to the dash & to the windshield) is unaffected, yet horizontal dispersion (side windows) is narrowed. Could this be why you like it so much...less reflections off the side windows as opposed to direct-radiated sound?


You can control directivity with three things. The shape and dimensions of the piston, a waveguide, and an array. Or all of the above.

I am using "all of the above." I intentionally used a large piston because it has a narrower beamwidth both vertically *and* horizontally. Then I stuffed it into a shallow waveguide. With the waveguide, the beam is still ninety degrees, but now it's operating all the way down to 2500hz. The crossover point is at 3khz. Also, vertical coverage is down to 500hz easily, because of the windshield. That's why you don't want it firing up, you want it firing towards the back window.

The whole reason I went to all that trouble is to keep the two beams from interacting, to preserver the stereo illusion. Remember, the whole reason this "trick" works is the following:


Above 1600hz, we're sensitive to frequency response more than location. That's why we can put tweeters in bizarre locations like this.
If the two tweeters interact with each other, it screws up the stereo illusion.
High frequencies are quite short - it doesn't take a large waveguide to control them. Or in JL's case, a sphere.
The side windows are screwing up our soundstage more than I'd ever realized.

You could improve upon this with a beam that was even narrower, say forty degrees instead of 90. Danley does this with his Synergy horns.

Anyways, long story short, the waveguide is there to keep the two beams from crossing, as much as possible, so they *don't* array.



mosconiac said:


> You've commented that you/we should tuck the tweeters into the windshield & dash to keep reflections off those surfaces nearly time-aligned with the direct-radiated sound. Therefore, controlling dispersion in that direction is not as critical.


Mmmm, it's still critical, but it's not too hard to just push them all the way back into the windshield, and that basically solves the problem. (This assumes you've created a beam already, using the piston's diameter, a waveguide, an array, or all of the above.)

If you don't want to create a beam, you can diffuse the off-axis response using a sphere. That's what JL did. A 2" sphere diffuses the off-axis response down to something like 2khz. Doesn't take a whole lot.


----------



## western47

PB,

Are you still working on a couple of small WG's to replace the small array posted in this thread. Narrowing the directivity even more has got to be a good thing in this scenario.

Any updates really help all of us that wait with bated breath.

Thanks.


----------



## solacedagony

Patrick Bateman said:


> Basically make the dimensions of the mouth equal to the crossover frequency. So with a crossover frequency of 3000hz, the mouth is 4.5" across.*
> 
> That's it!
> 
> Simple huh?
> 
> The depth of the waveguide will depend on how wide you want the coverage to be, and how big your radiator is. The reason that the Peerless can use a waveguide that's just 3/4" deep is that the radiator is so big to begin with. If it was a 1" dome the depth would be deeper.
> 
> * sound travels at a speed of 13500 inches per second.


As the waveguide becomes deeper, are you now introducing a time problem since the mid and compression driver are now not on the same vertical plane? I would imagine that initially it's so small that it doesn't matter, but I could imagine those deep pro audio style horn/wave guides having an audible effect.


----------



## Patrick Bateman

Here's an update on the project.

First, the bad news -

I spent the three day weekend building a bunch of different waveguide protypes. Basically the idea is to create a pair of narrow beams for the left and right high frequencies. To preserve the illusion of stereo we need to use something to control the directivity.

Anyways, I spent numerous hours building and testing a bunch of devices, and none of them were particularly successful:


I built a shallow waveguide for a Celestion compression driver. It was so shallow that it introduced a notch in the response, rendering it unusable for the most part.
I built a 2nd waveguide for the Celestion compression driver, where the first inch and a half used a 90 degree PVC elbow. By putting a bend in the path, I can keep the depth very shallow. (Which is important - we want this as far back as possible.)
According to Geddes, a flat piston is the ideal shape for a waveguide. I built a shallow waveguide for my TangBand flat-coned midranges, and measured that. It measured very nice, EXCEPT for a GINORMOUS peak at 15khz. Don't trust those TB spec sheets I guess. They show it, but it's WAY bigger in real life. Someone on the forum reviewed a similar model, and thought it was "bright." The peak that I'm seeing on mine could explain the peak that he's hearing. http://www.diymobileaudio.com/forum...-band-w4-1757sb-flat-cone-mid-full-range.html
The Peerless design, the one that I've shown in this thread, still worked the best. Smooth response, good extension, good power handling. The TangBand will get louder, but it has that nasty peak at 15khz.

Despite all this, I haven't given up on the Celestion. I think that with the proper waveguide it can exceed the Peerless.

But the Peerless is really REALLY nice - I've been running it for a couple weeks now, with no real complaints. And it's a heck of a lot less work than squeezing every last ounce of performance by using the Celestion and a WG.


----------



## Patrick Bateman

The Good news is that I came up with a solution to some of the issues I've been having with this set up.

When I first set this up, I was impressed by what a great sound stage you can get when the tweeters are so close together. I believe that this configuration "fools" the brain because the side windows and the windshield color the response of our speakers a great deal, and because our imaging cues are dominated by frequency response above 1600hz.

There were three things that I didn't like about the presentation:


*#1 - a lack of ambience*
The soundstage sounded very good, but it also sounded like a big pair of headphones. Everything is right in front of you. At first, this is very impressive; I've never heard sounds placed so convincingly. But the lack of ambience got to be a little weird after a while.
I tried a number of things to fix this. I don't have digital delay in my bag of tricks, so my midbasses are located equidistant to the tweeters. Because the pathlength to the center of the dash is relatively short, I had to locate my midbasses about a foot forward of the kick panels. This was purely due to pathlength; if I had digital delay this wouldn't be necessary. (Or if I could push the tweeters back further, which is what I'd rather do.)
I tried pushing the midbasses back to the kick panel, and that improved ambience a little bit. But mostly it just made thing less "intelligible." For instance, lyrics became more difficult to decipher.

So at this point in the project, I had two Peerless "woofers" on the dash, but I'm using them as tweeters because of their narrow directivity and extended response. The woofers are B&C 8NDL51s in sealed boxes, which I can put wherever I want. I tried various locations in the front of the cabin.

Then I remembered the experiments I'd done with rear-mounted midbasses in my Accord, way back in 2005. (check out audiogroupforum, they're documented there.) Back then I used the rear deck for my midbasses briefly, and found that it improved the ambience of the system as a whole. But I discarded the idea, because it screwed up my depth of stage. (This is one of the weird things about being super-tall; due to my height, my ears are actually closer to the REAR speakers than the kick panels. Particularly since I tend to recline the seat alllllll the way back.)
Since it *did* improve the ambience in 2005, I gave it a try in 2010. And sure enough, it worked REALLY well. There's an audible improvement in the stereo's ambience when you move the midbasses from the front to the back. Another reason that it works really nice in this setup is that the pathlengths are nearly *perfect.* Within two inches.
So this was a very nice surprise. The rear-mounted midbasses didn't work with my horns in 2005, but that was mostly because the horns were waaaaaay under the dash. I'd even cut up the car a bit to extend the pathlengths. In 2010, the rear-mounted midbasses work VERY well with the dash mounted tweeters, because the pathlengths are nearly equal. The fact that they're all on the same "plane" couldn't hurt either. Due to the shape of our ears, sounds which originate below us sound different than sounds which originate at eye level. This is why EQ can be used to fool people into thinking that speakers are higher than they really are.

Now before anyone runs out and rips out their midbasses, keep in mind that it's tricky to pull this off. The center mounted tweeters create a very convincing center image, but need a little "something" to generate some ambience in the cabin. Moving the midbasses to the back did just that. At the same time, the intelligibility of the presentation suffered a bit, likely due to the relocation. Also, when you turn your head, the illusion disappears. (One of my friends kept turning around to look at the speakers, all weirded out that she couldn't "hear" them  )

The next thing I'm going to try is adding a SECOND set of midbasses, equidistant to the first, but in the FRONT of the car. Like the Grand National.

*#2 - Distortion*
The Peerless drivers are not as "clean" as the compression drivers which I normally use. They're not "grungey", but there's only so much you can expect from a conventional 2" piston.








Parts-Express.com:Vifa NE85W-04 2-1/2" Full Range Woofer | Vifa NE85W-04 2-1/2" Full Range Woofer neodymium Aluminum Cone Full-Range Driver 4 Ohm extended range line array monitor point source aura tymphany09​To address this I'm considering a series of replacements for the Peerless, everything from Celestion CDX1-1425 in a waveguide, to BG NEO3 in a waveguide, to the new Vifa neodymium 2.5" driver, which appears to be an evolution of the Peerless woofers that I'm currently using. The Vifa is promising - it has a big fat heatsink to improve power handling, along with more displacement.

*#3 - Cosmetics*
This thing is ugly. Uhhhhh I'm really bad at making pretty speakers


----------



## 94VG30DE

In the Creating a Perfect Soundstage thread, you talk briefly about justification for using foam in the throat/mouth of the waveguide. In this instance, is that going to be necessary? Or is that negated due to the placement further inboard from the side windows, as well as the PVC rounds to smooth the array? I recognize that this is a considerably more shallow waveguide than the aforementioned, but it might actually clean up the look a bit to have foam/grill cloth across the entire front of the array anyway. Further helping smooth off-axis distribution could only be good, right?


----------



## Viperoni

I was going to ask about output but your latest post addressed that Patrick. I'll keep on reading this thread, it's got me very interested, awesome work!


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## Patrick Bateman

One thing I mean to mention -

In all of my other posts, I've been talking about how door-mounted midbasses are The Devil, and one one should use them, etc etc etc

And then in this thread I mentioned that near the door was the best location for the midbass(!)

Sorry about the confusion. The reason for this is because I can't get the stupid tweeters far enough back, and I don't have time delay. In the Unity projects the compression driver was at least six inches further back, because I did all kinds of tricks to wedge it all the way back. On top of that, the soundstage with the Unities seems a lot deeper because the _average_ distance to the tweeters is much further. (Since the passenger side tweeter is so far away, it makes the whole stage seem deeper.)

So this setup DOES have a stage that is shallower, though the image IS more believable than the Unity. Basically the Unity gets you a deep and wide soundstage, but it tends to shift to one side or the other, depending on what is playing.

This solution isn't as deep or wide as the Unity, but it doesn't wander, and I really like that. I also really like the articulation, and it's an easy install.

Anyways, THATS why I had a sudden change of heart on the door-mounted midbasses. I'm still not a big fan, but until I can come up with a way to get the tweeters another six to twelve inches back, it works better than the kick panels.

As mentioned yesterday, I've found that rear mounted midbasses work even better than that, and I intend to install SIX midbasses instead of two this week.

I'll be putting four up front, and two in the back. So the front midbasses will be much louder, but there *will* be some in the back.


----------



## lycan

Patrick ...

I've been re-thinking midbass arrays. I was originally quite negative on them, because they can tend to "collapse" the stage if not arrayed properly to the far left & right (on a wide circle-of-confusion). But I recently figured out there's a way around this  That's the good news.

The bad news is that there's still no way to solve the "head turning" problem with midbass behind you (and i've largely argued in favor of rear-mounted midbass). You can't tell front vs. back ... unless you turn your head 

In the midbass, it's ALL about ITD. That makes the problem nothing more than an intriguing geometry problem. And it also means that there's probably an interesting _optimization_ in a midbass array : maximizing output while minimizing magnitude response anomalies, and minimizing sensitivity to head-turning.

May i suggest that one of us start a new thread ... "midbass arrays revisited"?


----------



## Patrick Bateman

lycan said:


> Patrick ...
> 
> I've been re-thinking midbass arrays. I was originally quite negative on them, because they can tend to "collapse" the stage if not arrayed properly to the far left & right (on a wide circle-of-confusion). But I recently figured out there's a way around this  That's the good news.
> 
> The bad news is that there's still no way to solve the "head turning" problem with midbass behind you (and i've largely argued in favor of rear-mounted midbass). You can't tell front vs. back ... unless you turn your head
> 
> In the midbass, it's ALL about ITD. That makes the problem nothing more than an intriguing geometry problem. And it also means that there's probably an interesting _optimization_ in a midbass array : maximizing output while minimizing magnitude response anomalies, and minimizing sensitivity to head-turning.
> 
> May i suggest that one of us start a new thread ... "midbass arrays revisited"?




Do it!

I paid off my car on Monday, now I have even more money to throw away on zany car audio projects


----------



## Patrick Bateman

Patrick Bateman said:


> Parts-Express.com:Vifa NE85W-04 2-1/2" Full Range Woofer | Vifa NE85W-04 2-1/2" Full Range Woofer neodymium Aluminum Cone Full-Range Driver 4 Ohm extended range line array monitor point source aura tymphany09​To address this I'm considering a series of replacements for the Peerless, everything from Celestion CDX1-1425 in a waveguide, to BG NEO3 in a waveguide, to the new Vifa neodymium 2.5" driver, which appears to be an evolution of the Peerless woofers that I'm currently using. The Vifa is promising - it has a big fat heatsink to improve power handling, along with more displacement.




If anyone else is considering the new Vifa drivers, be sure to read the spec sheets carefully. I nearly purchased the 2" drivers instead of the 2.5" drivers, on the assumption that they would make a better tweeter. Then I noticed that the BIGGER driver has more extended response AND smoother response. This is totally backwards; you'd expect the smaller driver would play higher.

But if you look at the spec sheet, you'll notice the moving mass of the bigger one is much lower, which is why it performs so nicely.

It's kind of bizarre - I'm half tempted to email them to find out if the spec sheets are backwards.


----------



## sqshoestring

I'll chance to be the idiot here, if you have more midbass output in front the rears are not going to be much of a problem are they? Much of my tuning is based on that when it comes to rear fill, rear sub blending, etc. 

That is often my largest issue with lack of midbass in a car; because if you don't have midbass in front you can't turn up any midbass out of the subs/MB in the rear or they localize....if you have some MB in front, you can add some in the rear for significant MB total....to put it simply. IMO only about 50Hz and lower can be purely omnidirectional from a rear sub, above that needs some "help" from the front say 80Hz minimum needs to come out of the front at a significant level. That said I suppose it depends how high you go with MB, I tend to think 200Hz at most and prefer closer to 100 still at full output. 

Or, maybe have the EQ or install that can taper off rear frequency above that? Way back when I used to do a lot of rear deck IB installs, it was very important to have the right slope and xover on the subs to blend and have the right midbass....that was the key. For lack of a better description the midbass had to taper down under the fronts but still be there to beef them up. When it came out right the midbass and bass were full and powerful, there was no noticeable source from the rear with head turning. It could be done even with the old standard 6x9 in the rear that provided mostly midbass really, only rear seat people heard the highs/mids if it worked right. Some cars you would hear them turning your head I think the angle of the rear window/etc changed that. Some I set up with caps and resistors and/or faders. On the other hand everyone wanted 6x9 in rear deck because that is what people outside the car would hear, lol. At one point I ran two crossovers; a clean Nakamichi on highs and one I didn't like on subs only because it had adjustable slopes on it. Tried an EQ but most were noisy back then. I swapped a lot of subs getting that balance right with no EQ, was a pita but fun back then. Sorry to ramble.


----------



## 94VG30DE

lycan said:


> May i suggest that one of us start a new thread ... "midbass arrays revisited"?


For those playing the home game, lycan took some initiative, and posted. You can follow it here: http://www.diymobileaudio.com/forum/diy-mobile-audio-sq-forum/74088-midbass-arrays-revisited.html


----------



## Patrick Bateman

In a post that I made yesterday, I mentioned that I was working on improving three things. Lower the distortion, improve "spaciousness" and ambience, and improve the cosmetics.

Moving the midbasses to the back of the car improved "spaciousness," and I've been considering a few replacement drivers to lower the distortion of the Peerless drivers.

Here's my attempt to improve the cosmetics.









Here's the view from the outside of the car. You can see that a bit of paint would camouflage them well.








JL GTI for comparison. You can see the chromed pods peeking out









Here's a comparison of the old and the new​
_Here's some listening impressions -_
First off, it sounds *completely* different. So if you're thinking about trying either one of these projects, you should really consider building both and doing your own listening impressions.

_*First, the Bad News -*_
There's an immediately obvious reduction in efficiency. This is easy to fix, just insert an LPad on the midbass. I used 6dB.
The bigger issue that I ran into was that the rear-mounted midbasses *completely* screwed up the image with the spherical tweeters. I haven't spent a lot of time trying to figure out why this is; possibly due to the wider directivity of the spheres versus the waveguides. Anyways, I tried tweaking the crossover points, adjusting the LPad and the phase, and finally just moved the midbasses back to the front of the car. This isn't a dismissal of the rear-mounted midbasses. There's just something about the spherical tweets, they don't play nice in that configuration.
Another thing that I noticed is that the soundstage had a nice sense of "spaciousness" with the midbasses up front, and the spherical tweeters. This wasn't the case with the waveguide tweeters; when the midbasses were up front there was an unnatural lack of width. Again, a ton of this is subjective, so try it yourself.
I think what's going on here is that the spherical tweeters have much wider dispersion than the waveguide tweeters. Due to this, there's an improved sense of width, and you don't feel like anything is missing. With the waveguides you need to add something in the back to improve the ambience and spaciousness of the presentation. And due to the cone of confusion, it's not obvious that the midbasses are _behind_ you.
Keep in mind that this "spaciousness" is a bit artificial. In the first case we're using the rear mounted midbasses to add ambience, and the cone of confusion to fool the listener. In the second case we're widening the directivity, which increases the amount of reflected energy off the windshield and the windows, which also raises the ambience level. Though the spaciousness is basically being created out of thin air by intentional reflections, it does an excellent job of making the stereo sound less like a set of head phones, and more like a conventional set up, where the speakers are placed very wide.

_*Second - The Good News -*_
As much as I love waveguides, I can't deny that these spheres sound very natural. There's an obvious reduction in efficiency, but an improvement in smoothness.
The most obvious improvement with the spheres is that you wouldn't know where the speakers were located if you couldn't _see_ them. Acoustically, they disappear. If you've followed the sphere thread, you know that it doesn't take a big sphere to make a tweeter disappear; even the ones I'm using are much bigger than I need. In fact I could use ones that are four times smaller, but then the driver wouldn't even fit!
















The JL GTI​
One of the reasons I built these spheres was to compare the conventional location to the unconventional. With both tweeters very close together, there was a definite narrowing of the stage. This was much less pronounced with the waveguides, like because of their narrower directivity. I moved the spheres as far apart as I could, which basically put them in the exact same locations that JL uses. In this location, the stage moved from the center of the dash to the instrument cluster. I prefer it in the former location. To fix that, I just crossfired the tweeters. Be careful with this; turn the tweeters too far and the stage will widen, but a hole will develop in the center due to phase issues. Or at least that's what I was hearing. I used a very modest amount of toe-in, about ten degrees. It moved the stage over to the right a few inches, just enough to get things to sound "centered" again. If only it was this easy with a conventional set up!

The next thing I did was try the conventional set up. This is:
midbasses in the kicks, tweets near the A-Pillar

In this configuration, the stage was a *little* bit wider than the unconventional, _but not a whole lot!_ Kind of surprising, but that's psychoacoustics for you. If you can get those early reflections under control, you can do some strange things. With the conventional setup, the stage had shifted to the left, and it was also murky now. For instance, one of my test tracks has a piano in it, and the location of the piano keys was completely vague in the conventional setup. Every key sounded larger-than-life, and was blurred across the entire stage, but shifted to the left. In the unconventional setup the location of the keys varied, and their audible size was more "pinpoint" and less "fuzzy."

I'll definitely take pinpoint imaging over fuzzy imaging, even if their a bit less stage width. I plan on sticking with this configuration for the moment.

Of course I can't just clone what JL is doing though  After listening to compression drivers for years, I'm accustomed to high efficiency and low distortion. To take this to the next level, I'll be publishing some tricks that lower distortion, increase power handling AND efficiency, all for less than twenty bucks. Stay tuned...


----------



## CraigE

Here's what I've been working on the past few days. They are Dynaudio MD102 Tweeters in 1-1/2 " PVC caps.
The results are very good and similar to what Patrick has described.
I also have the Peerless 830970 drivers, and will try something with them.
Thanks Patrick.


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## fish

Craig that looks nice & unassuming. I can't tell by your pics, are your tweets "toed-in" at all?


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## CraigE

fish said:


> Craig that looks nice & unassuming. I can't tell by your pics, are your tweets "toed-in" at all?


Thanks, and something I like is that they don't interfere with the view from the driving position.
No "toe in" in the pix. I did fab hinges, which you can see, for vertical adjustment and they will rotate horizontally as well.
I will be trying a little "toe in" next.


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## JayinMI

stills said:


> a 2.5 way?


2 Girls and one who just works the camera? 

Jay


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## mitchyz250f

Patrick - When you say midbass, do you mean midbass/midrange (80 - 3000), or do you mean a true midbass (80-320)? Is this a two way or a three way. If it is a two way, do you think you could run a three way with the MBs in the rear, mids in kicks and spherical tweeters. Is there a minimum distance (1/4 wave) between the sphere and the dash and window? Looks like JL puts them right on the dash.

Have you tried any spherical conventional tweeters with greater dispersion as used by JL?


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## sydmonster

Posting for referal...


and a thank you to all who have contributed, particularly Mr Bateman. Cheers.


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## Patrick Bateman

Patrick Bateman said:


> I have a bunch of drivers at my disposal, but the key to this is to create a REALLY strong forward lobe.
> 
> For instance, JL is using a 1" tweeter, and due to the small diaphragm, the two drivers are going to interfere with each other in a huge way. I simulated them using the tools from FRD Consortium, and the two tweeters suffer from a ton of constructive and destructive interference.
> 
> If you use a larger diaphragm, a waveguide, or both, you can prevent them from interfering with each other for the most part.
> 
> It's the same idea as that pic I posted this morning - you get a beam right down the center of the car, and each person is listening to the same beam off-axis.
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> ​
> The woofers in the kick panels are B&C 8NDL51 in sealed boxes, the same ones from my 2001 Accord project on audiogroupforum. The tweeters are Peerless 2" woofers. I guess that isn't a "tweeter" per se, but they have output to 20khz and narrower directivity than a 1" diaphragm.
> 
> (And we WANT narrow directivity, to get the windows out of the mix.)




If anyone is too lazy to build an enclosure for the Peerless 830970, I found a quick solution. I was at Fry's Electronics yesterday, and stumbled across this:








This isn't a driver that's *similar* to the 830970, or a close cousin. This is *the exact same woofer.* I took some pics with my camera phone, just to be sure. I'll upload those later. It's a set called "Creative Gigaworks T3"

To give you an idea of how good these drivers are, the average set of computer speakers are $50. These are $280. So do the math


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## Fast1one

Patrick Bateman said:


> If anyone is too lazy to build an enclosure for the Peerless 830970, I found a quick solution. I was at Fry's Electronics yesterday, and stumbled across this:
> 
> 
> 
> 
> 
> 
> 
> 
> This isn't a driver that's *similar* to the 830970, or a close cousin. This is *the exact same woofer.* I took some pics with my camera phone, just to be sure. I'll upload those later. It's a set called "Creative Gigaworks T3"
> 
> To give you an idea of how good these drivers are, the average set of computer speakers are $50. These are $280. So do the math
> 
> [/font]


And this folks, is why you DIY for everything. Stellar quality drivers at a fraction of the price


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## jp88

Patrick,
have you thought of trying the dayton rs52 for this project? It should beam, has low distortion, and has considerably higher sensitivity


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## jimbno1

I have a question. If the idea is to minimize reflections is there any way to take advantage of a ribbon tweeter's vertical (when mounted conventially) almost complete drop off past the physical ribbon itself? Mounting horzontally? Of course I the lack of horizontal response would then make aiming of the tweeters towards the other side necessary which would cause reflection off the side windows etc.

When I say ribbons I am also including planar dynamic which would probably be much easier to install. Just wondering if it was worth considering?

Jim


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## BigRed

Just listened to CraigE's car with the tweeters in a similiar position as the old JL car.

Impressions: Very nice!! Solid center with just a hint of a narrower sound stage on songs that had hard left and right information. The staging was nice and accurate, and like Patrick mentioned, if you did'nt know the tweeters were there, you would not be able to tell with your ears. I would say a huge improvement over the door placement he had previously. I too hate a blurry stage, and the presentation now in his Vette is REALLY good!

Craig, way to Diyma your way to a huge improvement thru experimentation  Kudos to you my friend!!


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## Patrick Bateman

jp88 said:


> Patrick,
> have you thought of trying the dayton rs52 for this project? It should beam, has low distortion, and has considerably higher sensitivity


I like it loud, and that means a lot of displacement is required. You can get their via SD, via xmax, or both. The Dayton has more SD than a conventional tweeter, but the new drivers from Tymphany can equal it, while offering more xmax.

Maybe I'm just a sucker for low distortion, but their new line basically renders a whole swath of drivers obsolete. It's like the guys at Tymphany studied the Aurasound line, lowered the distortion, improved the build quality, and offered them up at the same price. They're *that* good...


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## Hernan

Patrick Bateman said:


> I like it loud, and that means a lot of displacement is required. You can get their via SD, via xmax, or both. The Dayton has more SD than a conventional tweeter, but the new drivers from Tymphany can equal it, while offering more xmax.
> 
> Maybe I'm just a sucker for low distortion, but their new line basically renders a whole swath of drivers obsolete. It's like the guys at Tymphany studied the Aurasound line, lowered the distortion, improved the build quality, and offered them up at the same price. They're *that* good...


How much I hate and love these RS52. Now I'm divorced!!! 
(they get loud!)


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## jp88

Patrick Bateman said:


> I like it loud, and that means a lot of displacement is required. You can get their via SD, via xmax, or both. The Dayton has more SD than a conventional tweeter, but the new drivers from Tymphany can equal it, while offering more xmax.
> 
> Maybe I'm just a sucker for low distortion, but their new line basically renders a whole swath of drivers obsolete. It's like the guys at Tymphany studied the Aurasound line, lowered the distortion, improved the build quality, and offered them up at the same price. They're *that* good...


From my understanding sd and xmax would more determine how low the driver could go not necisarily how loud (providing there is enough vd (sd*xmax) for a given volume at a given frequency) 

Since we are talking about using both of these drivers well above their intended frequency range wouldnt sensitivity and power handling be just as important?
rs-52 btw has a sens of 91 db 1w/1m and a power handling of 60 watts
the peerless driver we are speaking of (if Im looking at the correct one
830970 sens 82 db 1w/1m and a power handling of 60 watts ?

It would seem that the peerless would need ~10x the power to reach the same spl.

Correct me if Im wrong of course.


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## Patrick Bateman

I haven't been very active on the forums because I wound up getting involved with a big project at work (supercomputing, seriously!).

Anyways, things have quieted down a *little* bit, and I think it gives me an opportunity to do a "post mortem" on this particular project.

First, a recap:

The idea behind this project is to put the tweeters in a *very* unconventional location - the center of the car. JL Audio did it first, here's a pic:










At first glance, this seems really goofy, but there's some genuine science behind this. In a nutshell, at high frequencies our perception of location is dominated by _interaural intensitiy differences_. This is a fancy of way of saying that "if your left and right tweeter don't match, your soundstage is going to suck." It's also the reason that it's SO DIFFICULT to get tweeters to sound "right" in the car. Since we're so far off axis on one side, it's nearly impossible to get them to match.

Up until a few months ago, my preferred solution was to use a waveguide and cross-fire the tweeters. It's still a valid solution, and it's what I do at home. But putting the tweeters in the center of the dash is surprisingly effective.

If you don't believe me, try it yourself. It's easy. In my personal experience, I've found that tweeters in this location deliver a soundstage that's nearly as wide as a conventional location, but with improved intelligibility, and a soundstage which isn't overblown or artificial. For instance, if you listen to something in mono, it SOUNDS like mono, and a good stereo recording has width from window to window.

So far so good, right?

Unfortunately, I ran into a couple problems, and I've really been racking my brain to solve them.







Here was my first stab at putting the tweeters in the center. I know these don't look like tweeters, but that's how I'm using them. They're 2" drivers from Peerless. The funky looking baffle acts as a waveguide, to keep the left and the right from interfering with each other.

This configuration was easy to build, and it sounded quite good. My only gripe was that the high end lacked some "sparkle" and it couldn't get nearly as loud as I'd like. (These aren't efficient drivers, they're too small to be.)







Here was my third try. This time around, I built a pair of waveguides, and used compression drivers. By using compression drivers, I increased my efficiency A LOT, and also raised my power handling. (In this pic they're not 100% finished. You get the general idea though.)

This set was waaaaaay more work than the first set. And unfortunately, I'd have to admit that it didn't sound as good. My measurements showed that the power handling was improved, and the response was more extended. But there was one fatal flaw - it doesn't have the "ambience" of the first experiment.

If you're active on the other audio forums, you've certainly heard people rave about dipole speakers. Dipole speakers radiate energy to the front and to the back, and they're all the rage in the DIY community.

In my opinion, even though the second experiment measured better and was carefully orchestrated, the dipole radiation pattern of the first experiment was more pleasant to listen to.

If only it could take some power!







Of the three experiments, the second may be my favorite. In the second experiment I put an Aurasound 2" driver in a simple sphere. This is a very VERY basic enclosure, and a simple crossover.

While it doesn't appear that I'm using a waveguide, I actually am. _The shape of the piston and the enclosure itself_ alter the polar response of the speaker.

That paragraph is really important; it's something I didn't fully grasp, and it's very important when you're trying to get good sound in the car. _The shape of the enclosure, and even the shape of the cone_ alter the polar response.

In a nutshell, we have a very smooth and controlled transition from the diaphragm to the enclosure, without a sharp edge in sight. And that contributes to an improved polar response, which in turn makes everything sound more natural. It basically cuts down on listener fatigure.

At this point, you must be thinking, *if the second experiment is so great, why aren't you using it today?*

Unfortunately, the second experiment was hopelessly unable to get loud. It sounded awesome, and imaged great, but it couldn't even come close to matching the power handling of the compression drivers, and the efficiency of a sealed box is lower than the dipoles (in their passband at least.)

After spending way too many nights and weekends building prototypes, I believe that this is what we need to make this work:


To get a real soundstage, our left and right tweeter must match. By putting them in the center, that becomes a lot easier, because we're listening to both from almost the same axis. Note - this DOESN'T mean that we have to be ON axis; just that the left and right match. We could listen to both at 30 degrees, or 0 degrees, or whatever. Just as long as they both match. _Our perception of width and depth doesn't come from high frequencies_. That's why this trick works.
The dipole tweeters create a pleasant sense of ambience, but can't take the power. The compression drivers can take the power, but lack ambience. It's a catch-22; we want to cut down on reflections, but take it too far, and it sounds weird.
The spherical tweeters are an excellent compromise... If only they could take the power. Even if they could, they don't have the "ambience" of the dipoles.

So we need something like the dipoles, but with REAL efficiency and power handling.

Trust me, I tried about a gazillion solutions, everything from various waveguide contours, to line arrays, to bipoles... I couldn't come up with ANYTHING that let me "have my cake and eat it too."

Then I remembered a rave review from The Audio Critic, of the Beolab 5. Based on that review, I auditioned them at the B&O store in Portland Oregon, and they DO indeed live up to the hype. That was a few years back, and I ended up buying Gedlee Summas, but the B&Os are *very* nice. (And for sixteen thousand, they should be!)

Interestingly, the B&O solution and the Geddes solution are similar in some respects. The B&O speaker looks like it's supposed to be modern art, but it's actually functional. The Gedlee Summa uses a waveguide, and so does the B&O. The difference is that the B&O flips the waveguide on it's side. There's a lens too. In the Gedlee design the "lens" is called a phase plug, and it's inside of the compression driver.







Here's a pic of one of their speakers; the tweeter is mounted vertically, fires into a lens, and then a horizontally mounted waveguide. (no, that's not me.)






I am only aware of one car that has them - the Aston Martin DB9. (They pop-up, btw.)







For comparison's sake, here's my Summas. Tha cabinet behind it is SIX feet tall! There's a waveguide on top of the Summa, just to show the size.

:: whew ::

That was a long post!

If my hunch about the Beolab is correct, I believe we can take a dome tweeter, put it in the front of the car, then "transform" it's radiation. Doing this reduces reflections off the ceiling and the floor. At the same time, we're _intentionally_ restoring some of the ambience that's missing from this unconventional tweeter location.

The guys at JL also ran into this problem apparently; they ended up using a total of six tweeters. According to their article, the additional tweeters are used to restore ambience.

We can do the same thing, using a lens instead of additional tweeters. Is it a lot of work? Sure, but it's worth it. In my experience, it's VERY difficult to create a convincing soundstage with more than one tweeter per side. The added tweeters create more problems than they solve.

If you'd like to study this further, read these articles, or go and listen to a set of the Beolabs.

http://www.sausalitoaudio.com/pdf/SAU_ALMA_WPaper_R1.pdf

_The Use of an Acoustic Lens to Control the
High Frequency Dispersion of Conventional
Soft Dome Radiators
by David Moulton
Presented at the American Loudspeaker Manufacturers Association Symposium,
Las Vegas, NV, January, 1998.
Abstract
The beam width of conventional direct radiators varies as a function of wavelength and frequency,
leading to loudspeakers whose directivity varies widely as a function of frequency. At the same time, flat frequency response across an horizontal angle of 180° yields significant benefits in terms of imaging, timbre and room interface. The authors will discuss a lens that converts the output of a conventional radiator into such a dispersion pattern.

Précis

The Dispersion Problem

The dispersion of direct radiators varies as a function of frequency, tending to diminish as the frequency increases. This behavior is a direct result of the coupling of a direct radiator to open air. At wavelengths that are long relative to the size of the radiator, the dispersion of energy will tend to be omnidirectional, while at short wavelengths it will tend to be directional.
This means that, for a transducer with flat amplitude response on axis, at low frequencies (long wavelengths) the power output will be significantly greater than it is at high frequencies. By itself, this means that loudspeakers in reverberant rooms have deficient high-frequency performance, because
the summed direct and reverberant energy from a loudspeaker have a power spectrum that is rolled off compared to the power spectrum detected by a microphone used to make a recording intended for playback over that loudspeaker. Further, when loudspeakers are used in stereophonic pairs, the absence of high-frequency lateral dispersion diminishes the quality of the stereophonic illusion, because the lack of high-frequency information in the reflections reduces the clarity, robustness and depth of the
perceived phantom images.
Traditional Design Practice For Dealing With Dispersion
Direct radiators are traditionally mounted in baffles. The dispersion characteristics of any given mounted
driver are either accepted as is, or else “smoothed” by the use of gentle and conservative wave guides which are intended both to reduce diffraction effects and to make dispersion more uniform and/or narrow. Some manufacturers attempt to reduce baffle size to enhance dispersion. In general, highfrequency dispersion of +/- 15° at a -6 dB point is considered acceptable, +/- 30° at a -6 dB point is considered to be good performance, and +/- 45° at -6 dB is considered to be excellent in conventional
loudspeaker performance. Generally, no modifications to the transducer itself are undertaken to modify driver dispersion.
Acoustic Lens Technology In Principle
Acoustic Lens Technology (ALT) incorporates a lens and a conventional soft dome radiator into an integrated unit, so that the actual dome is partly enclosed in a concave chamber and partly enclosed in a convex chamber that is exposed to free space. The geometry of the lens is based on a radial continuum of elliptical sections that in combination create what can be thought of as a “wave-gathering-andspreading mechanism.” The lens redirects the acoustic energy by 90°, so that in a normal application,
the driver is facing upwards and the lens directs the sound into a horizontal dispersion field approximately 180° wide and a vertical dispersion field approximately 30° high.
The power output of a driver is normally radiated into free space (yielding power coverage of approximately 270° by 270° on average) with the great majority of that power output in the lower frequency range of the driver. The ALT lens redirects the power into a much smaller solid angle, approximately 30° by 180° as noted above. At short wavelengths the lens acts approximately as a raytracing reflective device. At longer wavelengths, the lens functions in a manner somewhat analogous to a horn, leading to increased directionality at such wavelengths and frequencies. Interference effects and phase problems are minimized by the elliptical geometry at higher frequencies and by the comparatively long wavelengths (i.e. reduced phase shift per unit of time delay) at lower frequencies.
In summary, the power output of the driver is radiated into a comparatively small solid output angle of 180° by 30°, is comparatively free of lobing and other interference effects, and is approximately constant as a function of frequency.
Acoustic Lens Technology In Application:
Two Lenses In A Three-Way System
A successful three-way prototype run has been constructed that employs ALT lenses for the midrange and high-frequency drivers. The drivers are high quality commercially available drivers, and the lenses were optimized to match their behaviors.
Crossover frequencies are lower than would be normal for these drivers, at approximately 300 Hz.
(normally about 800 Hz.) for the woofer/midrange crossover point, and 1800 Hz. (normally 4 kHz.) for the midrange/tweeter. Because of the constancy of the dispersion and the minimal phase shift problems, the crossover points are extremely smooth on and off axis, and the family of response curves at 0°, 30°, 60° and 90° in the horizontal axis are extremely similar, albeit with a slight loss in relative level at 90° of about 6 dB.
1U.S. Patent No. 5615176
Commercial Development
As we have developed this lens, it has become clear to us that the lens is more properly thought of as a modification to driver technology than to loudspeaker system design. The performance of the lens is absolutely related to the performance of the driver, and the development of any particular driver/lens combination needs to be carried out prior to its incorporation into any loudspeaker system. Such a developed driver/lens can then be specified for use in loudspeaker systems. The actual horizontal and vertical dispersion characteristics of the lens can be modified for different applications, given a suitable driver. Specifically, the vertical dispersion can be changed for various
applications, while retaining broad horizontal dispersion. For sound reinforcement applications, for instance, extremely thin but wide dispersion can be obtained, while in a fixed close environment such as an automobile, vertical dispersion can be increased to accommodate a broad range of listener head heights.
In a fully developed and finished form, an ALT driver/lens can be easily incorporated into a wide range of loudspeaker systems. It is suitable for applications such as conventional high fidelity loudspeakers, home
theater speaker arrays, in-wall speakers for distributed sound systems, automobile sound systems, and concert sound reinforcement applications._


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## timelord9

so the trick is to reverse engineer and DIY one of these types of lenses? The benefits in car of having a 30degree by 180degree radiation seem obvious, as it negates the windscreen and dash reflections (although not the side window reflections...?)


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## audiogodz1

Congrats on post 1000 Patrick. (if that is accurate)


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## bassfromspace

I think it may have been stated earlier but the BG Neo 3 or 8 may be the solution for output and ambience.


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## flamefox850

what if we use 4 tweeters in total ?

2 of them in left & right A pillars while the other 2 in the center of the dash.

4 of them are ring radiator tweeters which is known for their narrow dispersion or u can say weak off-axis performance so that u can 'point' the tweeter at the correct way.

The right and left tweeter (A pillar's) aiming on-axis to both driver and front passenger respectively while the right center tweeter aiming to driver and the left center vice versa. Adjust the gain so that the center will not going to be too loud.

Can we achieve two-seat center with this method ?


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## Patrick Bateman

flamefox850 said:


> what if we use 4 tweeters in total ?
> 
> 2 of them in left & right A pillars while the other 2 in the center of the dash.
> 
> 4 of them are ring radiator tweeters which is known for their narrow dispersion or u can say weak off-axis performance so that u can 'point' the tweeter at the correct way.
> 
> The right and left tweeter (A pillar's) aiming on-axis to both driver and front passenger respectively while the right center tweeter aiming to driver and the left center vice versa. Adjust the gain so that the center will not going to be too loud.
> 
> Can we achieve two-seat center with this method ?



I'm not a fan of using multiple tweeters. Path lengths are king at low frequencies, and matching your tweeters is king at high frequencies. Imagine if you were trying to illuminate both seats using four rays of light, but all four of them were pointed in different directions. While it's *possible* to illuminate one seat fully, you can't illuminate both. If you wanted to illuminate both seats fully, _the best solution would be one wide beam covering both._

Obviously, that would be mono, and we don't want that. The weird thing about this configuration is that it's _clearly_ in stereo. I've tried it with one tweeter instead of two, and the difference is immediately obvious. On a well recorded song, the entire stage collapses when you use just one tweeter.

The guys at JL are clearly aware of this; they noted that the pathlengths to the tweeters were chosen so that three on each side summed as one. Unfortunately, pathlength isn't very important at high frequencies, particularly when we're listening to some of the tweeters on-axis and some of them off-axis.

Again, this is just my opinion; Manville Smith might disagree. But I personally believe that this is a very good solution, we just need to use one tweeter per side, then "dial in" the ambience.

The way that we can "dial in" the ambience is via manipulation of the reflected energy. And we do that by playing with the directivity, and the distance from the windshield and the dash.







Here's another pic of the Aston Martin, to give you the general idea.

Another "neat" psychoacoustic trick is that we *should* be able to move the tweeters forward from the windshield, since pathlength isn't important at high frequencies. That helps to reduce reflections from behind the tweeter. Then again, the Aston Martin has the tweeters as far back as possible. It's possible that the energy is so focused _forward_ that reflections off the windshield are a non-issue. Only one way to find out...

As for the use of a ring radiator, actually it's the other way around. A radiator will begin to "beam" at a frequency equivalent to the piston's diameter. Ring radiators have a smaller diaphragm than a conventional tweeter (due to the hole in the center) and a phase plug.

Because of that, their dispersion is *very* wide.

You can see it in the measurements from John Krutke:

Zaph|Audio







XT19 ring radiator















Compare the XT19 to this tweeter, a Vifa D26NC55 dome. With a diameter of 1", we'd expect the Vifa to start beaming at 13500hz. In John's measurements, the off-axis response is down by 6dB at 14000hz. So the "rule of thumb" is quite accurate in this case.


----------



## eng92

Some of the more upscale Audis and MB AMGs are offering the same B&O ALT pop-up tweeters. 

Bang & Olufsen Advanced Sound System - 2nd generat - Bang & Olufsen

For the AES library members here, the B&O paper on this is:
11277 "Driver Directivity Control by Sound Redistribution"

It presents some background theory as well as the results of their FEM and BEM modelling compared with empirical data.


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## otis857

THe B&O tweeters look interesting. Patrick, are you going to experiment with this design? Also, Im wondering how much of the concave section of the lens should wrap around the side of the tweeter to control the horizontal patern and the side window reflections? As pictured in the Audi's on the B&O website, it looks like there isnt much side reflection control, mostly verticle and rear (towards the w/s) dispersion control. But how cool would that be to have pop up tweeters?


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## lycan

Something to always remember ...

You might think you're only using two tweeters, when in fact you are using many, many more  A tweeter "array" is absolutely unavoidable in a small, reflective environment (unless we employ waveguides or other directional elements).

Image theory of reflections tells us that we can substitute an "image" or "phantom" driver for the reflective surface. The _phantom_ will be located wherever you "see" the reflection of the primary driver. What this means is that (at least for wavelengths where the tweets radiate strongly in all directions) EACH tweeter creates at least THREE phantoms : left side window, right side window, and windshield. So you think you "only" have TWO tweeters? Think again ... you've got at least EIGHT 

Draw the diagram of primary-plus-phantoms, and some interesting observations emerge. For example :

- As you move your primary tweets closer together up on the dash, in which direction are the phantoms moving?

- Is it better to aim you primary tweets more on-axis, or the aim the phantom tweets more off-axis?

The last point is interesting, in that it helps expose the pure folly of "on-axis" tweets in a small, reflective environment. Which of the 8 tweets do you think you're aiming "on axis"? 

Note : i've used the phrase "small, reflective environment" quite carefully. By "small", i mean small enough so that the reflections arrive _well_ within the Haas (or precedence) limit. By "reflective", i mean enough reflective surfaces nearby (like glass) that will reflect substantial energy in the treble.


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## rogan

I'm doing a mid & tweeter dash pod laid out horizontally in the near future. I always thought it was best to keep the tweeter to the outside of the mid (ref Buwulda red ebay car where the tweet was almost touching the side glass) but this thread appears to say stage width doesn't come from the tweeter. So is it better to have the midrange on the outside and the tweeter on the inside?


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## Patrick Bateman

rogan said:


> I'm doing a mid & tweeter dash pod laid out horizontally in the near future. I always thought it was best to keep the tweeter to the outside of the mid (ref Buwulda red ebay car where the tweet was almost touching the side glass) but this thread appears to say stage width doesn't come from the tweeter. So is it better to have the midrange on the outside and the tweeter on the inside?



As far as stage width goes, both the tweeter and the midrange are important. The thing is, our perception of imaging cues varies with frequency. At high frequency, it's all about frequency response, and that means that both tweeters have to match.

That's difficult to do in a car, because we're listening to one on-axis, and one off-axis. (In a typical set up.)

This is an atypical setup, obviously.

One of the reason that the Buwalda setup might work is that reflections are worse when you're a few inches away from a reflective surface then when you're _right next to it._ This might seem a bit counterintuitive, but true.

The stock tweeters in my car are right next to the glass, and the reason that this works is that it drives the reflection up in frequency, where it's less audible. Common sense would say that it's a lousy location, but it works due to the frequency of the reflection.


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## Patrick Bateman

otis857 said:


> THe B&O tweeters look interesting. Patrick, are you going to experiment with this design? Also, Im wondering how much of the concave section of the lens should wrap around the side of the tweeter to control the horizontal patern and the side window reflections? As pictured in the Audi's on the B&O website, it looks like there isnt much side reflection control, mostly verticle and rear (towards the w/s) dispersion control. But how cool would that be to have pop up tweeters?


I've heard the Beolab 5s, and thought they sounded quite good.
http://theaudiocritic.com/plog/index.php?op=ViewArticle&articleId=34&blogId=1
Peter Aczel uses them as his reference, and he has a review available online. Aczel used to run Waveform Acoustics, which is somewhat similar to my reference speakers. Aczel has a habit of infuriating audiophiles, but I've always enjoyed his magazine. I used to pick it up a newstand in Hollywood back when I was in college.

I *haven't* heard the Beolab 3s, but based on the reviews I've read, they offer a significant percentage of the performance of their big brothers, but in a much smaller package.

So my plan is to clone the 3s.

Cloning a $3200 Speaker for $400 - diyAudio

If you want to do a "straight ahead" clone, it appears that you can get all the parts from Madisound. Based on the pictures, Beolab is using Peerless woofers along with two passive radiators. The speakers retail for $3200 a pair, and the woofers are $13 each. :: ouch ::

Finally! A Loudspeaker That Raises the Bar, by Dave Moulton
The designer of the lens has been forthcoming in providing information on how it works.

But my idea is a bit different than a straight ahead "clone." Basically, the ideas behind the Beolab are "scalable." If you want them to run to 30khz, you could do that by just changing the dimensions.

So that's what I intend to do. Take the Beolab 3, but reduce the dimensions even further.


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## CraigE

Just a heads up to anyone purchasing the Peerless 830970 2" Full Range Driver from Parts Express.
I talked to PE, and those were a buyout item. 
They still use the 830970 part number, but the driver looks much different.
The closest they have (to the buyout item) is the 830983 which could be the same, except for the color of the cone and dust cap.
The tech could not access the specs from the older part number for comparison.


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## RattyMcClelland

So anyone else tried this?
I will attempt this soon out of pure curiosity as its seems ridiculous but im not one to judge as i haven't tried it yet. 
Will be interesting to see though as i have the HAT L1pro SE and they are ring radiators with a wide dispertion. Midbass (HAT L6) in the kicks. Crossover point at around 5k.


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## 94VG30DE

Half-tried it, then got distracted with other projects. Basically where I ended up was it was REALLY localizable, and the sound had two distinct sources. Some of that is my door installs fault (which I am working on right now) and part of that I think is due to my inadequate job of mating the baffle edges to the windshield and dash. You can see it on my build thread here: http://www.diymobileaudio.com/forum...ld-log-finally-56k-maybe-ok-3.html#post988167


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## rdv

i tried it with alpine xt19's. i was waiting for funds to get a tweeter that could cross at around 2k but i couldnt wait so i decided to experiment with the alpines. i just plopped them on the dash of my crv without any baffles, just bare tweeters to get an idea of how they might sound. i positioned them similar to the JL mounting. i initially tried a cutoff of 2k as a start but this was really too low so i ended up with about 3.5k where they sounded smooth and not strained.

the mids are seas md18's mounted in the doors and cut off a little lower than the tweeters

i must say that i am really happy with imaging and localization. despite the fact that they are just roughly double side taped to the dash and aren't pointed that straight. to test them out i listened to the audiophile voices cd and the singers on most of the tracks were firmly planted in the center of the stage/dash with proper ambience. i also liked that instruments that should be centered were centered as well. i used to hear them off to the side when my tweeters were placed either on the dash or the kicks.

a negative for me would be that my stage has narrowed. not that much but definitely noticeable compared to when my tweets were mounted on the sides. its not annoying though and definitely still listenable. i am still going to mount them properly and/or change them but for now they are still there and i am happy enough not to move them (no pics right now)


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## thebetaproject

RattyMcClelland said:


> So anyone else tried this?
> I will attempt this soon out of pure curiosity as its seems ridiculous but im not one to judge as i haven't tried it yet.


I gave it a quick go using the peerless 2" without the wave guide (I know the wave guide is intergral to the design, no flames please) and also std. dome tweeters. On some material is sounded outstanding and on others so-so. One problem to me was that the soundstage width appeared to be contracting and expanding with some tracks the 'wobbling' soundstage IMHO it was quite distracting. Maybe the JL fix of using super tweeters in the miror sails would help this. When I get more time I think I'll go back and try it with the extra super tweetrs in the sails.


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## rdv

I agree with the width issue although the effect for me isn't as bad. The stage sounds to me like it could benefit from tweeters placed on the sides of the car. Or maybe some mids playing really high


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## Patrick Bateman

thebetaproject said:


> I gave it a quick go using the peerless 2" without the wave guide (I know the wave guide is intergral to the design, no flames please) and also std. dome tweeters. On some material is sounded outstanding and on others so-so. One problem to me was that the soundstage width appeared to be contracting and expanding with some tracks the 'wobbling' soundstage IMHO it was quite distracting. Maybe the JL fix of using super tweeters in the miror sails would help this. When I get more time I think I'll go back and try it with the extra super tweetrs in the sails.


It's a trip huh? That was the most shocking thing about this setup. On really well recorded songs, the width extends beyond the boundaries of the car. But on 75% of the tracks out there, it basically sounds like mono.

I don't think this is a problem with the speakers. In fact, I'd argue the problem is in the mix. A lot of music out there is basically mono, with some soundstaging tricks thrown in here and there.

Having said that, I still agree with you. A lot of the time I wished there was more width, even if it was fake. Of course this is easy to do, and you're on the right track. Just add a couple more tweeters.

Ideally you'd wire up a couple of potentiometers so you could fiddle with the stage width, depending on whether the music is well recorded or not.


----------



## thebetaproject

Patrick Bateman said:


> I don't think this is a problem with the speakers. In fact, I'd argue the problem is in the mix. A lot of music out there is basically mono, with some soundstaging tricks thrown in here and there.


I agree, maybe we are hearing it closer to how it really is recorded and with this setup panned stereo recordings become immediately obvious. 


Patrick Bateman said:


> Just add a couple more tweeters.


I've bought some cheap Dayton tweeters to try out in the mirror sails. I hope to give it a go this week, I'll report back on how it goes. 

On a side note, a thanks to Patrick for bringing his ideas forward. It's given me the insperation get in the car and try out different things. There must be a better way to get a good soundstage in the car.


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## Candisa

I didn't take the time to read this entire thread trough, but I know what's it about: the possibility to use only 1 tweeter running mono because the human ear uses it only for height keys, BUT...

there is 1 problem in a car, especially in a 2-seater-install: the "sweet spot" is too big compared to the distance you're sitting from the tweeter to reduce the frequency response difference of what your left and right ears are picking up and this will cause problems. 
Also, music made with instruments won't have notes in the tweeter-range that don't have harmonics in the midrange (which is stereo), but in electronic music, everything is possible, so I'm sure there are tracks out there that really need stereo highs to sound correctly.

Isabelle


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## thebetaproject

Candisa said:


> I didn't take the time to read this entire thread trough, but I know what's it about: the possibility to use only 1 tweeter running mono because the human ear uses it only for height keys, BUT...
> Isabelle


This was the original idea but it quickly moved onto using two drivers (L&R) centered on the dash in different guises.

I went back and tried using additional ambience/super tweeters in the mirror sails, similar to the JL implementation. I tried them on the sails so that they would be directly above the bass/mids + also it’s any easy position to place them. For the two main tweeters I used Monacor DT-284S which have a nice and smooth off axis response, wedging them as far forward as possible around 15” apart, centered on the dash. This was very similar to Patrick’s original position for the Peerless. For the ambience tweeters I just used a 1uF cap inline as a crossover/attenuation, listening to them they didn’t seem to output much but it was just enough, probably 2uF would have been better on the 4ohm tweeter.

The ambience tweeters solved the problem of the contracting and expanding soundstage. It also made sounds seem more natural when panned hard left or right, before they could sound odd as the tweeter and mid/bass were so far apart. The sound stage whilst not giving perfect imaging it was very ambient, vocals sounding very natural and for lack of a better word _pleasing_. The biggest surprise was that with no EQ, time alignment etc. it just worked and immediately sounded good, especially given how far the dash tweeters are away from the bass/mids and the path length difference between the bass/mids in my car.

I listened to this for some time on different tracks and genres but I still found it odd with the soundstage centered on the middle of the dash. This is a personal thing as I prefer mine centered in front of me but for two person listening, this could be a winner.


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## Jarick

I'm going to jump in here with a couple questions...

- With a gigantic dashboard (Nissan Murano), would some of those complaints of a too-narrow soundstage be minimized?

- Would ring radiators work better than dome for this kind of setup?

- And if I had both ring radiators and dome, which would I want to use as the "super tweeter" at the corners and which would I want to use as the "main tweeter" in the center?


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## Patrick Bateman

Jarick said:


> I'm going to jump in here with a couple questions...
> 
> - With a gigantic dashboard (Nissan Murano), would some of those complaints of a too-narrow soundstage be minimized?
> 
> - Would ring radiators work better than dome for this kind of setup?
> 
> - And if I had both ring radiators and dome, which would I want to use as the "super tweeter" at the corners and which would I want to use as the "main tweeter" in the center?


Common sense says that our tweeters should be as far and as wide as possible. Obviously we get a lot of our stereo cues from our tweeters, and besides, it's a lot easier to move a tweeter around than it is to move a midbass around.

But psychoacoustics doesn't agree with the common sense solution; it says that our perception of high frequency location requires that the left and the right tweeter are carefully matched. Taken to the extreme, one might argue that a single tweeter is superior to a pair of poorly matched tweeters. That's what inspired this thread.

After a few months of experimentation, I personally found that excellent results could be achieved with a solution that falls somewhere in the middle. You don't need your tweeters all the way out to the edge. In fact, I was able to achieve a much better soundstage by pulling the tweeters towards the center. *Be sure to locate your midbasses carefully. If they're close to the center, you'll have no width whatsoever.*

Also, I found that pulling the tweeters forward didn't affect stage depth much at all. At this point, I really think that the location of midranges and midbasses has a bigger impact on the stage width and depth than anything else.

In a nutshell, narrowing the tweeters solidified the center image, and image width didn't suffer. In fact, on many tracks the soundstage was wider, but it was highly dependent on the source material.

These are my experiences; experimentation is highly recommended. And it's cheap and easy to do it!


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## Jarick

On my lunchbreak (hehe), I threw the silk dome tweets in the middle, tried toeing in and out, it all sounded way too centered and still too harsh (too bright up there!). I think for these particular speakers and in this car it wouldn't work, but I could really see a 3-way working wonders. These particular woofers and tweets have too low a crossover so it all sounded like it was coming right from the middle, and I'm passive right now.

I think I'll hook up the Alpine ring radiators tonight though and try it again. Probably won't stick. I'm pretty sure I'll be running the tweets in kicks for this install.

Very cool idea though, and I like people playing with the cheapo "full range" drivers.


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## thebetaproject

Jarick said:


> These particular woofers and tweets have too low a crossover so it all sounded like it was coming right from the middle, and I'm passive right now.


I tried the peerless speakers down to 500hz when on the dash, semi open baffle in a similar way to Patrick's original. This had the benefit of lifting the sound stage right up, on the down side it did make the collapsing/wobbling sound-stage problem even worse. My later experiment with the ambiance tweeters showed they do help prevent the collapsing, so maybe if another set of drivers in the sails also covering 500hz upwards (playing at a much lower level) would have resolved this. Normally multiple drivers covering the same frequency is a recipe for disaster but who knows what will work in car.

Regardless of the crossover frequency, the peerless running semi-open baffle did make the sound more ambient, natural sounding and fill the dash better than using std. dome tweeters. I reckon if it sounded harsh it's more down to the EQ or your speakers as I found easier to get a good sound with them on the dash.


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## mosconiac

Jarick said:


> ...These particular woofers and tweets have too low a crossover so it all sounded like it was coming right from the middle...


This isn't an application for a typical speaker compliment with crossover at 1.5-2.5k. It's bound to fail.

I've experimentally found that I lose the ability to locate tweeters around 4k..._maybe as low as 3.5k_. Therefore, we need a crossover point somewhat higher than that so we don't have significant contribution of the tweeter below that threshold. I would start experimenting around 5-6k and try a little lower...and a little lower...until it fails.


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## ib2qwik2c

Awesome thread! 
What if the tweeters installed like in the JL vw car were pointed on axis towards the driver? 
It looks like the goal here is to create a correct sound stage for both front seats? Would it be easier if the goal was to prioritize on the driver seat only?


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## thebetaproject

ib2qwik2c said:


> What if the tweeters installed like in the JL vw car were pointed on axis towards the driver?


Didn't make a huge difference, the tweeters placed in the mirror sails where only there to stop the soundstage collapsing on content with alot of mono. 


> It looks like the goal here is to create a correct sound stage for both front seats? Would it be easier if the goal was to prioritize on the driver seat only?


The only places I could get the twin peerless concept to work were the original position Patrick used and directly infront of the driver on the dash, see a pic here Anyone tried individual L&R speakers for driver and passenger? - diyAudio
Using the ambient tweeters with this was quite stunning, worked even better if the outer tweeters and bass mids were time aligned for the driver.


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## ib2qwik2c

very interesting..


----------



## The A Train

this could be a dumb comment but wouldnt time alignment solve all of this? i guess im not feeling the idea of a single tweeter. ive noticed on some songs, especially live tracks, you can locate independent sounds when using dual tweeters. this could just be a noob talking though


----------



## mosconiac

ameuba10 said:


> this could be a dumb comment but wouldnt time alignment solve all of this? i guess im not feeling the idea of a single tweeter. ive noticed on some songs, especially live tracks, you can locate independent sounds when using dual tweeters. this could just be a noob talking though


I'll leave the technical details to the experts, but what I can say is from my experiments...I can not localize high frequency information (above about 3.5-4k). The imaging cues you are experiencing are probably much lower in frequency that you realize.

My experiments consisted of using the signal generator resident to WinISD to sweep up & down the treble range on my home theater & note where I began to stop localizing the "phantom image". Over about 3.5k, the sound goes from being a point between the speakers to being "everywhere". Unfortunately, it also confirmed that I can not hear freq's above ~15k. 41 years of age & countless ear-ringing rock conerts later & I can't hear mosquitos. LOL

If you've never done the above, you should take some time to do it. It's VERY educational.


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## mosconiac

Does anyone have anything new to this intriguing thread???


----------



## diebenkorn

CraigE said:


> Thanks, and something I like is that they don't interfere with the view from the driving position.
> No "toe in" in the pix. I did fab hinges, which you can see, for vertical adjustment and they will rotate horizontally as well.
> I will be trying a little "toe in" next.


CraigE you have got a pm.


----------



## tinctorus

Ive been thinking about this lately for my new build and since I have 2 tweeters from my comp set already and plan to use them would there be any harm in placing BOTH tweeters center dash back towards the windhsield??

And if so how should they be aimed?
Directly towards the back of the car or should they be angled towards me in the driver seat?


----------



## Ludemandan

Patrick, I'm going to try using tweeters in circular enclosures on my dash. My central vent, and thus my available mounting width, is 14". You say the farther apart they're spaced the better. Yet, the idea is to minimize path length difference, which would suggest placing them as close together as possible. What should I use as a starting point? It will take a little time and effort to change it around.


----------



## Patrick Bateman

mosconiac said:


> Does anyone have anything new to this intriguing thread???


Guess who's got the day off work?

Audio Psychosis • View topic - A Soundstage with Width and Depth.

A bazillion updates can be found here.


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## Patrick Bateman

I received this email today, and thought I'd respond to it "in thread."

_I have been talking to Ralph of ambiophonics and he has been very helpful. I also realized that you had not put the ambiophonics in your car and I thought you had. So the questions I am asking you maybe not be answerable yet but I wanted to ask. This is the response I got from Ralph (hopefully it will be to your benefit as well)


"Yes, several people have had Ambiophonics working in a car. Once the unit is programmed it will indeed work without the computer. But you will have
to have the computer working in the car while you see what settings work best in your situation. The major problem with cars is symmetry. The AmbioDSP assumes that the levels and distance from each speaker to the driver are the same. You can balance the levels with the output level control provided, but each speaker must be reasonably equidistant from the driver's head. So normally, you cannot use the speakers that come built-in to a car with rare exceptions. Also the angle needs to be around 20 degrees or so. You can also use two speakers for the passenger seat. They are normally far enough to the side not to interfere with the driver's pair.

But if you can mount two speakers on either side of the steering wheel, for example, the results should be good. Let me know if you get it to work"

My questions are about using your or any horns instead of two speakers? Would this work? And as far as the other speakers they would be playing below 250 hz would there be any phase/time issues with the ambiophonics?

Thanks again
Judd
_

I've experimented with this, and I found that a physical barrier worked the best. In my case, I used the center console of my car to cancel the crosstalk. In a nutshell, the left and right speakers are on either side of the center console, pushed right up against the firewall.

*In this location, I was able to create a wide soundstage with and excellent center image.*

The second best location was with both speakers in front of the driver, and up on the dash.

The worst location was the one that Ralph recommended, with the speakers under the steering wheel. If I had to hazard a guess, I'd bet that the lack of a physical barrier confuses imaging cues.

My car has a prominent instrument cluster, so I'd guess that's one of the reasons that speakers work so well in front of the driver, flanking the instrument cluster. (The cluster is reducing crosstalk.)

But the best sound by far leveraged the center console for crosstalk elimination. *In this configuration, the stage was as good as I've heard in a car.*

More details can be found on my forum. (forum.audiopsychosis.com)


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## Ludemandan

To the person who asked the question, MiniDSP has a rear ambience program with independent delay correction for each channel.


----------



## diebenkorn

Thank you for your help, this is awesome news and I am going to try this hopefully today. I am still confused in whether you were using your horns or conventionals in the best set up? I have been thinking about places for mids without cutting up the car and came up with a boxed (wood) mid 5 or 6 inch where people install their horns (under the dash) and it would be downfiring. I am sure somebody has done this, any thoughts or feedback? Edit found the GNIB box and answering some of my own questions. Patrick if you get your horns or whatever you are using down to 150 hz or somewhere around there what are your plans for the lower frequencies?

I am sure the pics will answer this but where did you put the driver side speaker? I keep running into pedals and other obstacles.


----------



## Patrick Bateman

diebenkorn said:


> Thank you for your help, this is awesome news and I am going to try this hopefully today. I am still confused in whether you were using your horns or conventionals in the best set up? I have been thinking about places for mids without cutting up the car and came up with a boxed (wood) mid 5 or 6 inch where people install their horns (under the dash) and it would be downfiring. I am sure somebody has done this, any thoughts or feedback? Edit found the GNIB box and answering some of my own questions. Patrick if you get your horns or whatever you are using down to 150 hz or somewhere around there what are your plans for the lower frequencies?
> 
> I am sure the pics will answer this but where did you put the driver side speaker? I keep running into pedals and other obstacles.


I've answered your question on my forum.


----------



## winegamd

I have had this thread saved for about three months and just finished reading and playing with tweeter positions. I have T/A so I dont have to worry about tweeter placement too much, but still wanted to play with this idea just to see the results. Well, I have to say it was exactly as stated. After about 2 hours of listening and testing I learned quite a bit. 

1) As long as the tweeter is crossed above 3k it does not matter if they are in the corners of the dash or in the middle, the center image and stereo image from 3k up does not change. I had to be really open minded while testing and adjusting T/A just to be sure I was not convincing myself that the T/A made a difference. The reflections are the only difference in being able to tell where the tweeters are located. I ran for most of the day with the t/a on the tweeters zeroed and on for the mids(no sub right now), then I got to thinking, if the left mid is delayed and in alignment then there have to be some phase differences of the source material at the crossover point. 

2) I ran white noise and played with the T/A and there where phase discrepancies near crossover like I hypothesized. T/A is still necessary if you can not match pathlengths for the mids and the tweets. Since my mids are currently in the doors and the tweeters on the dash I still need T/A for phase alignment at crossover. 

3) The most important frequencies in sound reproduction for staging is in the 600-3000. So, now that I have exploited the limitations of my system I am convinced now that a three way/four way with tweeter, midrange, midbass, and sub is necessary for achieving the most accurate acoustic image, at least in my car ('06 GTO). If you can find a mid that can have solid midbass that keeps up with your subs, plays to 3k, and fits in your kicks then a two way will work. I can not put my 7" exclusives in my kicks as they would interfere with my driving since the car is a stick. 

All of this playing really makes me want to buy a second car with large kick panels, a large dash, and an automatic to build a two seat system. I used to think that was an impossible undertaking, but now I think it can totally be achieved and with no T/A. Kind of makes me wish I still had my '94 Caprice.


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## Ludemandan

winegamd said:


> 1) As long as the tweeter is crossed above 3k it does not matter if they are in the corners of the dash or in the middle, the center image and stereo image from 3k up does not change.


So would you say it was an improvement, or irrelevant? I have wires routed through my center dash vent right now, ready for a tweeter installation when I get around to it, and wondering where I should set my expectations. I am going to cross them over high, like 4k-5k.


----------



## winegamd

I would say try it and see if you like it. If you don't, put them at the ends of the dash. The omni directionality only remains constant if you can get rid of reflections/diffraction off the wind shield and side windows or A-pillars. Otherwise you get delayed reflections and it starts pulling to either side. Also, dont forget about the angle as tonality must match for each side for this to work. I just happen to be lucky enough that I can tuck my tweeters far enough in the corners of my dash that they are close enough to all reflective surfaces that the first 1/4 wave is not subject to diffraction. You may not be so lucky.

I will say that in the center the stage width can get narrow, but just as Patrick observed, it is dependent on the mix, where at the ends of the dash it is almost always wide. It is a subjective thing. I myself prefer the sound at the ends of the dash, as even with headphones, the sound is never narrow whether it was recorded that way or not. Either way give it a shot as you will learn multitudes about your hearing, the way the sound behaves in your car, and which frequencies are the most important and hardest to reproduce accurately.


----------



## Brian10962001

When I was in college I traded a Honda Accord I was driving for a 1986 Pontiac Grand Prix (the RWD Monte Carlo style GP). The car was a 1 owner, before my friend purchased it, had less than 100k on it, and my friend wanted out from under it because the window motors had both quit working about 1/8 of the way down. I had the window motors replaced within a week, and was hurting because my Accord was set up (Kicker tweeters in the top of the doors, McIntosh 5.25's, Fosgate deck, pair of 15's in the trunk). 

This car had 2 3.5's in the dash in an impossible to get to position, and a 4X10 hole in the center of the dash with a grill that someone had already pulled out. It sounded terrible, I put my 15in Hollywood Excursion's running off a Lanzar OPTI 1000 mono in the trunk and it didn't help matters at all, the car had 0 high frequency anywhere. It sounded like it had a sharp crossover at 3k hz or so (and it didn't give it that nice warm tube amp sound, it was just not there). 

I did what I could, and dropped down some wires from the 4X10 hole and placed a pair of tweeters smack dab in the middle of the dash. I lined them with butyl tape on the bottom and basically made a sound deadened little pocket for them to sit in. I was shocked how well that worked out. I got several compliments from my friends on it and no one ever guessed the tweeters were in the middle. 

I always just thought it was because of the refraction off the windshield, but looking at this there was probably more to it. The strangest thing was the car even sounded proper with the windows down.


----------



## evilbass

...


----------



## Patrick Bateman

winegamd said:


> I have had this thread saved for about three months and just finished reading and playing with tweeter positions. I have T/A so I dont have to worry about tweeter placement too much, but still wanted to play with this idea just to see the results. Well, I have to say it was exactly as stated. After about 2 hours of listening and testing I learned quite a bit.
> 
> 1) As long as the tweeter is crossed above 3k it does not matter if they are in the corners of the dash or in the middle, the center image and stereo image from 3k up does not change. I had to be really open minded while testing and adjusting T/A just to be sure I was not convincing myself that the T/A made a difference. The reflections are the only difference in being able to tell where the tweeters are located. I ran for most of the day with the t/a on the tweeters zeroed and on for the mids(no sub right now), then I got to thinking, if the left mid is delayed and in alignment then there have to be some phase differences of the source material at the crossover point.
> 
> 2) I ran white noise and played with the T/A and there where phase discrepancies near crossover like I hypothesized. T/A is still necessary if you can not match pathlengths for the mids and the tweets. Since my mids are currently in the doors and the tweeters on the dash I still need T/A for phase alignment at crossover.
> 
> 3) The most important frequencies in sound reproduction for staging is in the 600-3000. So, now that I have exploited the limitations of my system I am convinced now that a three way/four way with tweeter, midrange, midbass, and sub is necessary for achieving the most accurate acoustic image, at least in my car ('06 GTO). If you can find a mid that can have solid midbass that keeps up with your subs, plays to 3k, and fits in your kicks then a two way will work. I can not put my 7" exclusives in my kicks as they would interfere with my driving since the car is a stick.
> 
> All of this playing really makes me want to buy a second car with large kick panels, a large dash, and an automatic to build a two seat system. I used to think that was an impossible undertaking, but now I think it can totally be achieved and with no T/A. Kind of makes me wish I still had my '94 Caprice.


There's a bit of a "catch-22" with this narrow tweeter business. If you put the tweeters close together and near the center of the dash, you get a nice center image, almost as if there's a center channel there. By keeping the midranges wide, you get the best of both worlds (width AND a center.)

The problem for me has been this perception that the frequency ranges are "disconnected."

I stumbled across an intervew with Bob Carver that has some interesting insights into how to get this sorted out. Details here:

Audio Psychosis • View topic - Ultra Small Midranges


----------



## Hardtofathom

Has anyone looked at the TS-S062PRS stage 4 mid range from Pioneer? They say it can play from 80-40,000hz. If so couldn't this be used in place of both a mid range and a tweeter on your dash?


----------



## Patrick Bateman

Another forum member gave this a try* and wrote:

_"I tried this a month ago.
Tweets all over the middle of my dash.
Sounded goodat first, but went back to pillars after listening fo.r a while.
I just couldnt get it to work"_

^^ That experience is consistent with my experience also. At first it sounds good, and you dig out all your recordings with great imaging. And you hear the soundstage in a way that you haven't heard it before. But after a while, it gets old. In my situation, this was because *most recordings just don't have any soundstage.* So recordings with a good soundstage are 'decoded' in a way that I've never heard before. But recordings with little or no soundstage, which is MOST recordings, sound mono. (As they should.)

So it's really tricky. The truth is that the speakers are just 'decoding' the mono soundstage properly, and so the stage sounds narrow. As it should - it's mono. But the artificially wide soundstage that you get with a conventional stereo setup playing back mono recordings is more pleasant.

An example of this is AM radio. In my car, with a conventional setup, the sound comes from both sides of the car. But in an opsodis setup, it's going to sound like it's just in the center, and that can sound pretty dull.

And the thing that sucks is that a lot of popular music is basically mono, with a smattering of studio effects.










I've been having some good luck with the Beolab lenses. The reviews on them are good too. Here's a couple quotes:

_"It's the detail that impresses most about these really rather magical speakers. They project a soundstage way up above their top-plates, and deliver wide-open and highly credible pictures of instruments and voices almost regardless of where you sit in the room. The strike of finger on an acoustic guitar string is just as readily revealed as a pounding bass and drum combo." (B&O BeoLab 9 review from the experts at whathifi.com)

"I immediately noticed that the stereo stage was conveyed with an unusually realistic depth and solidity, and that the image didn't collapse to one side as I listened from off center. In fact, I got a reasonable stereo image even while listening from directly in front of one of the speakers. I had encountered this phenomenon only a couple of times before, first in a speaker invented by Mark Davis and made by dbx in the late 1980s. Its claim to fame was an unusual radiation pattern designed to produce this wide-seating-area effect, so I knew that the BeoLab 5 was not a conventional box speaker. But it didn't sound like a flat-panel dipole or bipole model either, since the sound was clearly not coming from a tall source. It also lacked the sometimes excessive spaciousness you get with such speakers." (Bang & Olufsen BeoLab 5 Speaker | Sound and Vision Magazine)_

Here's my .02 on why this radiation pattern is good for a car:

At high frequencies, our perception of the location of a sound is based on intensity. For instance, if the sound is supposed to sound like it's coming from our left, our brain makes that determination based on how LOUD the sound is.

In a car, this is a problem. Because with conventional dome tweeters up in the A pillar, the soundstage is always dragged to the left. This is simply because we're too close to the left tweeter. And there's no way to move the tweeter further away, short of putting it into the kick panels. Which opens up other problems.

One 'fix' would be to simply reduce the level of the left channel. That creates two problems however. The first problem is that it makes the imaging for the passenger even worse than it already is. The second problem is that our perception of low frequency location is NOT based on intensity!

So, unfortunately, tweaking the balance of the left and the right tweeters creates more problems than it fixes.









Here's the on and off axis response of a Dayton RS28. In the measurement, we see that the output level varies with angle. (This is why people aim their tweeters obsessively.)

Unfortunately, this is another one of those 'unsolvable' problems. The output level varies with angle, so what do you do? This means that the location of sounds in the soundstage is going to vary with frequency. At 2khz the center of the stage is a completely different spot than at 8khz, due to the varying directivity of the tweeter.










Here's the same tweeter, but in one of the B&O lenses. *Now the response doesn't vary by angle any longer.*

This might have the potential to be the 'ultimate fix' for these soundstage problems. With the output level consistent from left to right, we now have a situation where *the locations of sounds in the soundstage doesn't vary from octave to octave.* If there's a voice coming from left of center at 2khz, it will also be coming from the same location at 4khz, because the directivity is not varying.

Keep in mind, this lens I built is *very* rough; I cut it by hand out of plywood. So you could do a lot better with more patience.


If the last few paragraphs made sense, then it might explain why the Beolab has such potential for the car. As noted earlier in the thread, the tweeters in the center of the dash image well because we get our high frequency imaging cues based on *intensity.* (And putting the tweets in the center of the dash equalizes the intensity by physically moving them to a point where they're equidistant from both driver *and* passenger.)

The Beolab lens equalizes the intensity also; by 'spraying' high frequency energy in a 180 degree arc across the soundstage. As my measurements demonstrate, it doesn't really matter where you sit; the sound is about the same level from left to right.

The nice 'upside' to this is that it should restore the stage width that's missing in the OPSODIS setup.


----------



## emilime75

I just read through this thread and had a couple of questions...some things aren't perfectly clear to me.

1. Are the tweeters run stereo, or mono?

2. Are small ring radiators a good choice for this? I have a pair of Vifa OT19NC00-04 3/4" Fabric Dome Tweeter 4 Ohm 264-1122 I thought I would try.

I have The Madisound Speaker Store and Vifa XT25SC90-04 1" Dual Ring Radiator Tweeter 264-1014 in the kicks? Should I keep the tweeters in the kicks connected? If yes, should I bandpass them? Currently, midbasses in the doors run 70-300, midranges run 300-4500 and the tweeters take over from there. 

I know experimentation is the way to go here, I just want a good direction to start in.


----------



## Patrick Bateman

emilime75 said:


> I just read through this thread and had a couple of questions...some things aren't perfectly clear to me.
> 
> 1. Are the tweeters run stereo, or mono?


They're run in stereo. In the original paper the author raised the idea of running one tweeter in mono though.

There's basically two reasons this works. First, at high frequencies, our perception of location is based on the intensity of sound. We literally don't have a way of perceiving where a high frequency sound is located, except based on it's intensity. Think of a mosquito for instance; the only way that you can tell if a mosquito is close or if a mosquito is far is by rapidly observing if the sound of the mosquito is getting LOUDER or QUIETER. In fact, you could probably tell where a mosquito is with your eyes closed, because your perception of a mosquito's location is based almost 100% on the intensity of it's sound.

Make sense?



emilime75 said:


> 2. Are small ring radiators a good choice for this? I have a pair of Vifa OT19NC00-04 3/4" Fabric Dome Tweeter 4 Ohm 264-1122 I thought I would try.
> 
> I have The Madisound Speaker Store and Vifa XT25SC90-04 1" Dual Ring Radiator Tweeter 264-1014 in the kicks? Should I keep the tweeters in the kicks connected? If yes, should I bandpass them? Currently, midbasses in the doors run 70-300, midranges run 300-4500 and the tweeters take over from there.
> 
> I know experimentation is the way to go here, I just want a good direction to start in.


I'm still trying to sort out these questions. In the Opsodis paper, the high frequencies are located immediately in front of the listener, the midrange is located at about 10 o'clock and 2 o'clock, and the midbasses are at 9 o'clock and 3 o'clock.

But it seems to me that one might be able to use a setup where the high frequencies are simply consistent from the left of the soundstage to the right of the soundstage. As far as I can see, the only reason for the high frequencies to be in front is because putting the high frequencies in front equalizes their intensity. (IE, when we have tweeters in the A pillars, like most cars do, it makes the left tweeter louder than the right tweeter, because the left tweeter is closer. So Opsodis counteracts that, by physically relocating the tweeters to the center of the stage.)

So, it SEEMS that one way to get the same effect would be to have a high frequency 'unit' that has the same intensity level no matter where you sit.

The reason that I say 'high frequency unit' and not 'speaker' is that you might use an array. I know that Durwood has done more experimenting with this than anyone, and he had an array of drivers that spanned the width of the dash at one point. And that seems like a viable solution.

But an array creates other issues too; the primary problem being that it's really hard to get the drivers close enough. To get a seamless transition from one driver to the next, the drivers should really be within about one third of a wavelength. And at 20,000hz, that means the drivers should be about half a centimeter apart! Which is basically impossible.

So that basically rules out an array for this project, IMHO.

High frequency waveguides might work.

And, YES, very small tweeters are attractive too.










The main issue the last two solutions is that *any* type of obstruction between the driver and your ears is going to screw up the illusion.

In the pic above, it looks like there's a straight line from the tweeter to the driver. *The problem is that sound tends to 'wrap around' as the wavelengths get lower and lower,* and when it wraps around, it reflects off of the windshield, and that screws up the illusion. One solution to the 'wraparound' problem is to cross the tweeter over at a point where it's starting to 'wraparound.' This is easy to calculate; it's the wavelength that's equivalent to the diameter of the tweeter. If you're using a 1" tweeter, that's 13,500hz. Adding a waveguide can lower than frequency, because a waveguide basically controls the wavefront down to the diameter of the waveguide. For instance, with a 3" waveguide, that frequency drops to 4500hz.

The spherical tweeter enclosures work nice; people have had a lot of good things to say about them in my thread about that. The reason that the spherical tweeters work is that the sound still 'wraps' around the enclosure, but as it wraps around, *it's radiated in all 360 degrees.* So you still get those 'cues' that screw up the illusion of where your tweeters are, but now there's a thousand subtle cues instead of one or two strong cues.



Wow, this is turning into a REALLY long post.



If anyone actually made it this far, here's a quick summary:

1) We want the sound of the tweeters to be the same, from the left of the car to the right of the car. At high frequencies, this is the recipe for good imaging.
2) The Opsodis arrangement works because putting the tweeters very close together equalizes the sound from left to right. (IE, one side isn't louder than the other side.)
3) The problem with tweeters in the A Pillar is that sounds 'wraps around' the radiator, and is reflected by the windshield. To combat this, one could use a waveguide to 'funnel' the sound forward, or a spherical enclosure to 'scatter' the sound in all directions. Basically we don't want strong reflections off the glass to give away the actual location of the tweeter.
4) There's a really annoying catch-22 with small tweeters. Small tweeters have very wide directivity and that's GOOD because it means that the sound of the tweeter will not vary as you move from left to right. (Because of the wide directivity.) But that's BAD because it also means that the sound will wrap around the enclosure   









I keep thinking the B&O lens solves problem #4. Because it *looks* like the lens would have 360 degrees of radiation. But it doesn't; it basically radiates into 180 degrees horizontally, and about 20 degrees vertically. So it's just about perfect to prevent these early reflections from happening.


----------



## Orion525iT

So I tried this today just to experiment. I combined knowledge gleaned from two other threads, one regarding the Opsodis paper and another regarding tweeterless setups. In the Opsodis thread, Patrick was trying to understand the wide stage he experienced in a stock, new car system. In the tweeterless thread, Andy was fairly adamant that full range drivers are a marketing misnomer, and will always loose out to proper use of tweeters. 

In my case I was trying to make an ultra simple and and inexpensive setup using mid bass drivers and full rangers only. The full rangers are 2-speaker arrays run from ~150hz to 20khz mounted in the kicks slightly inboard of the 8" mid bass. The 8" run from 25hz subsonic filter to 140hz. They (the arrays) do fairly well, with good center and chin level stage height, but have the annoying habit of being extremely sensitive to positioning. Additionally, with some songs the center stage will pull left and wander a bit. This likely due to beaming, and I believe is part of Andy's argument.

So I wired in some center mounted tweeters just for fun. I can't easily mount mid-bass in my doors without serious construction effort. But the attempt was a quasi-Opsodis; 8" mid-bass flush mount in the kicks, full range (I know Andy hates the term) arrays just inboard of the 8", and stereo tweeters a few inches apart run center dash as far forward as possible. The center tweeters run off passives from 2500hz-20khz. I _did not_ band pass the full range arrays, I simply left the 150hz high pass. 

Very interesting results. To me, the center stage is better, without having an overly strong or artificial bias. This may be in part due to the full range drivers running without low pass. I think the stage is actually larger; slightly wider with a bit more depth. There is some messiness and lack of cohesion, likely due to near reflections of the tweeters off the dash and windshield. Also, I can not time align anything, so there are slight differences in PLDs between left and right arrays and between the arrays and the center mounted tweeters. My impressions may change, but in my initial testing, I seem to have solved the wandering center problem presented by the full range arrays. I want to experiment some more with this, I am going to try to equalize the PLDs and get some sound absorbing materials up on the dash and part of the windshield to try to kill the early reflections for the tweeters. Pretty cool stuff!


----------



## helosquid

Patrick,
Thank you very much for your educational posts. I feel like I learn something every time I read your posts. Do you have any updates for us by chance?
David


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## BigRed

have you heard the audi with the B&O offering? it sounded like crap.


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## Patrick Bateman

helosquid said:


> Patrick,
> Thank you very much for your educational posts. I feel like I learn something every time I read your posts. Do you have any updates for us by chance?
> David


I've actually been a bit discouraged with trying to get something to work in the Mazda


----------



## Patrick Bateman

BigRed said:


> have you heard the audi with the B&O offering? it sounded like crap.


I've heard the top of the line Beolab.
I also DIY'ed some of the lenses.

Some observations:

1) The Beolab doesn't "sound like crap." It sounds spacious and dynamic. It *does* sound different than a conventional tweeter, and this can take some getting used to. I bought some Vandersteens last week, with conventional drivers, and I have to admit that they're really hard to listen to once you get accustomed to constant directivity. The Vandys do image really nice though.

2) I was surprised how well the DIY Beolab lenses work. They're fairly easy to build, and the shape doesn't have to be perfect.


----------



## asawendo

Great Patrick! I'm building one for myself...


----------



## BigRed

Patrick Bateman said:


> I've heard the top of the line Beolab.
> I also DIY'ed some of the lenses.
> 
> Some observations:
> 
> 1) The Beolab doesn't "sound like crap." It sounds spacious and dynamic. It *does* sound different than a conventional tweeter, and this can take some getting used to. I bought some Vandersteens last week, with conventional drivers, and I have to admit that they're really hard to listen to once you get accustomed to constant directivity. The Vandys do image really nice though.
> 
> 2) I was surprised how well the DIY Beolab lenses work. They're fairly easy to build, and the shape doesn't have to be perfect.


let me rephrase my statement. I think the Audi offering and how it sounds as an audio system in that car sounds over-processed and staged terrible. It was blurred. Tonally it was ok.


----------



## Patrick Bateman

There's an old post here that implies that it might be possible to make this setup work with two speaker locations.

In this post here http://www.diyaudio.com/forums/mult...riment-part-1-introduction-3.html#post2125835, a diyaudio member named kstrain mentions that the Geddes Harper speakers can be used as "bass-mid" in an OSD setup.

I'd read that post before, but glossed over the fact that the tweeters would be up front, similar to this:









So basically, you'd have two tweeters on the dash, and then midrange and midbass somewhere between 9 o'clock and 10:30

Might be an easy and effective setup for the car.

I personally tried three of variations on OPSODIS, and neither were something that I could live with for long.

First I tried it with two speakers very close together, like this, with processing:








With this setup, you get a really pinpoint soundstage. You *definitely* hear things well outside the boundaries of the two speakers. *But the dynamics just suck.* Basically the crosstalk cancellation kills the bass. And bass is a big part of dynamics.

I tried with a barrier, literally a big board between the speakers, and that worked even better I think. The soundstage isn't as big, but the dynamics are good.

But the barrier solution is completely impractical for a car.

Another problem with the barrier solution is that low frequencies don't sound spacious. It's hard to describe what I mean by this. Basically what's happening is that high frequencies, above 1khz, will often seem like they're coming from a location that exceeds the width of the speakers. I know this sounds hard to believe, with two speakers located right in front of you. But it's true. Our perception of high frequencies is based on amplitude; you can perceive that a high frequency sound is coming from your left even if the speaker is right in front of your face.

But those low frequencies are tricky; they're so long they're bigger than your head. So a physical barrier doesn't cut it. (250hz is over four feet long.)

So perhaps a hybrid approach is in order; tweeters in front, with a little bit of crosstalk cancellation. And mids and midbasses out to the sides, possibly with no crosstalk cancellation at all.

This type of a config is pretty close to the VW Jetta I heard that imaged so nicely. (Albeit with no processing on the tweeters.)


----------



## Regus

Patrick, did you notice any issues in the Jetta as regards the midrange? I don't know what crossover frequencies VW were using but I'm wondering whether you would get the same problem as you do with tweeters mounted in sail panels or A-pillars i.e. being closer to one side than the other messes with the IID and pulls things to the drivers side. I hope not, as it seems to me that an OPSODIS approach could help mitigate many of the shortcomings of the car audio environment.


----------



## Patrick Bateman

Regus said:


> Patrick, did you notice any issues in the Jetta as regards the midrange? I don't know what crossover frequencies VW were using but I'm wondering whether you would get the same problem as you do with tweeters mounted in sail panels or A-pillars i.e. being closer to one side than the other messes with the IID and pulls things to the drivers side. I hope not, as it seems to me that an OPSODIS approach could help mitigate many of the shortcomings of the car audio environment.


The only real problem I noticed what that most recordings suck.
So I'd sit there, and 75% of the time there's just no hint of a sounstage at all, and then something would jump out and *pow*. A real image.

The nice thing with having the mids and midbasses closer was that it basically widened the stage.

For instance, let's say I listened to a Radiohead track. It's well recorded, and there's a real image there. With the speakers in front of me, there's a nice stage, because it's in the recording. Now I switch to a podcast, and now the sound seems to be about 8" wide, because it's mono.
Once you put the mids and midbasses further apart, it seems to preserve the good imaging, while widening the stage. (Which makes everything sound bigger; even mono.)

I'd be really curious to hear this type of setup with processing enabled on the tweeters, but *not* on the midranges or midbasses. That might offer the best of both worlds. The width and pinpoint imaging that you get from crosstalk cancellation, without the lack of dynamics that comes when you apply the processing at low frequency.


----------



## Patrick Bateman

Someone emailed me on another thread. Thought I'd post the reply here because it's more "aligned" with this thread.



gijoe said:


> Patrick, we've talked a bit about the post you made years ago regarding using a single tweeter, it came up during the acoustic lens discussion.
> 
> How much stereo information is there (typically) above say 5kHz? If I wanted to try experimenting with a single tweeter setup, what is the best way to process the signal? Is it simply a matter of doing L+R?


I know the idea seems completely wacko but I've been running this way for about six weeks and I don't notice any missing information.

Still haven't decided if I'll use one or two tweeters for the car.

Trying to get the mono signal is a real p.i.t.a.

Don't do it passively, you can blow up your amp and your processors if you use a y-cable. (You can use a y-cable to SPLIT a signal but if you use it to SUM a signal you're asking for trouble.)

I looked high and low for a processor that would produce a full range mono output along with stereo outputs. You would think this would be common but I couldn't find one.

The only thing I found that works for this is the miniDSP 2.1 advanced.

I emailed them and they sent me this:

_"Hello John,

Thanks for your interest in our products.
Yes, the 2.1 advanced would indeed be the one you need (i.e. mix to mono). It doesn’t have to be LPF at all. There are LPF and HPF on all outputs. Just put them to bypass for these mixed to mono channels and you’ll be good to go. 
Another plug-in is the 2×4 advanced :http://www.minidsp.com/products/plugins/2×4-plug-ins/2×4-advanced-detail

This plug-in has a matrix mixer doing all you need.

Hoping this info helps.

Best Regards 

miniDSP Ltd 
Unit 1204, 106 how ming street 
Kwun Tong, Hong Kong 
Tel: +852 23582066"_


----------



## gijoe

Hmm, that complicates things. With my P99RS it's difficult to justify a miniDSP just to experiment. I wonder if I could build a simple summing circuit to do this, I haven't finished my engineering degree yet, but I'll see if there is a reasonable DIY option.


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## Patrick Bateman

If you have enough channels, try this:

1) low pass your left and right tweeters at 5khz
2) add a third tweeter in the center and high pass it at 5khz

This thread stretches back five years, and when I first tried it had a couple of full ranges in the center of the dash. That was way more spacious than I expected, but stage width was still narrower than a "real" stereo triangle.

But I've found you can get the best of both worlds with the setup described in this post. To my ears, it sounds like stereo, but the tweeter in the center fills in the hole you get with stereo. I've seen people go to amazing lengths to get a solid center image, and if people knew it was as simple as sticking one tweeter there they'd be amazed.

The really cool thing about all of this is that it fills in the hole in the center so well, you can REALLY drag your left and right speaker far apart. In the setup that I have currently, the only thing stopping me from widening the speakers further is that the room won't allow it.

Anyways, it's really easy to do if you have an extra tweeter laying around and an active xover. If possible you might move the center tweeter away from boundaries because that will make it sound "airier"


----------



## cajunner

Audio Control System 90?


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## Patrick Bateman

lol that would work

anything over $100 is off my radar

my midranges are two dollars each


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## cajunner

in one of lycan's tutorial threads, there was some talk of producing a summed l+r that went along with producing a l-r for surround...


seemed relatively easy, without the delay part put into the mix...


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## gijoe

cajunner said:


> Audio Control System 90?


If anyone has one I can borrow that would be great, haha! Without knowing how this will work I am not willing to spend much at all.


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## Patrick Bateman

cajunner said:


> in one of lycan's tutorial threads, there was some talk of producing a summed l+r that went along with producing a l-r for surround...
> 
> 
> seemed relatively easy, without the delay part put into the mix...


I think that if you have a head unit with dual stereo outputs you'd be fine. I'm using an iPad for a source so I have to go active.

I saw a thread on a prosound forum that would produce a mono and a stereo output passively, but it killed your stereo separation.


----------



## whisky22

Patrick Bateman said:


> If you have enough channels, try this:
> 
> 1) low pass your left and right tweeters at 5khz
> 2) add a third tweeter in the center and high pass it at 5khz
> 
> This thread stretches back five years, and when I first tried it had a couple of full ranges in the center of the dash. That was way more spacious than I expected, but stage width was still narrower than a "real" stereo triangle.
> 
> But I've found you can get the best of both worlds with the setup described in this post. To my ears, it sounds like stereo, but the tweeter in the center fills in the hole you get with stereo. I've seen people go to amazing lengths to get a solid center image, and if people knew it was as simple as sticking one tweeter there they'd be amazed.
> 
> The really cool thing about all of this is that it fills in the hole in the center so well, you can REALLY drag your left and right speaker far apart. In the setup that I have currently, the only thing stopping me from widening the speakers further is that the room won't allow it.
> 
> Anyways, it's really easy to do if you have an extra tweeter laying around and an active xover. If possible you might move the center tweeter away from boundaries because that will make it sound "airier"



Any specific reasoning for 5k crossover? Ear sensitivity at frequency? I tried lowering to 3.15 k but sounded much "thinner." For my car 6k works even better. I put the upgraded OEM dynaudio woofer/tweeter center channel in (L-R) and it made a big improvement in quality with noticeable R side guitar, L sided bass. Not sure about height/width but I'm still learning.


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## whisky22

just found this with B&W speakers


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## cajunner

looks like Audiofrog grills.


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## Patrick Bateman

whisky22 said:


> Any specific reasoning for 5k crossover? Ear sensitivity at frequency? I tried lowering to 3.15 k but sounded much "thinner." For my car 6k works even better. I put the upgraded OEM dynaudio woofer/tweeter center channel in (L-R) and it made a big improvement in quality with noticeable R side guitar, L sided bass. Not sure about height/width but I'm still learning.


Go grab a tape measure.

Now measure the distance from your left ear to your right ear. I have a giant head, so for me, it's about 13.5".

Now calculate the frequency. Sound travels 13,524 inches in a second, so 1khz is 13.5" long. (13,524/1000)

Due to that fact, we localize sounds about 1khz by amplitude. IE, it's largely based on the shape of your ear. Below 1khz, we localize sounds by phase, basically our brains calculate the arrival times below our two ears.

In the two octaves between 500hz and 2000hz, it's a combination of both, because those two octaves are in the 'transition period' between phase and amplitude.

But as you go higher and higher in frequency, above 2000hz, you're more dependent on amplitude. And as you go lower and lower, below 500hz, you're more dependent on phase.

TLDR: at high frequency, it's all about amplitude. And simply having two tweeters, or five tweeters, or ten tweeters, or whatever, is a compromise. As you go higher and higher in frequency, *the optimum tweeter isn't a pair of tweeters, it's one tweeter.*

At low frequency, it's all about phase. So you can have two woofers or a hundred woofers, *the only thing that really matters is that those woofers are equidistant.* (Because it's all about phase.) One of the reasons that subwoofer arrays work so well is that they randomize those reflections, because those reflections are basically the same as a real woofer. (IE, if you have one subwoofer, your reflections are going to be virtually as strong as the original signal.)


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## stills

Think I'm gonna give it a go. 

I'm putting Dayton rs-150-4's in my doors. I plan to cross them over at @ 3.5khz initially. 

I have a rockford rfq-5000 for center channel processing. I'm going to use my center AC vent to mount a speaker. 



I can go up to a 2" driver. The vent opening is @ 2.25 x 3.5. I suppose I could go larger if I opened up the blank vent. I wonder if a single driver will be loud enough.


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## Orion525iT

I have messed with this a few times now. I tried it again this morning, mainly because I discovered I had completely f'ed up the TA when I tuned my system last time (It's almost embarrassing how I managed that). Midbass in doors 120-1000hz, mids in kicks 1000-5000hz, single tweeter 5000-20000hz l+r through processing on the minidsp 2x8. All on 24 db LR slopes. 

First, I will say that I have not been able to get midrange kicks to work in this car, even though I have tried multiple configurations. The main issue is rainbowing. With a single tweeter, it makes this situation much worse. My attention was always drawn directly to the tweeter location in the center of the dash. If I attenuated the tweeter down, I could get it to the point where it's location was not obvious. Unfortunately, at that level, the highs sounded too muted and the "sparkle" was gone. The image seemed to have an false center, with too much concentration of the stage towards the center of the car. Maybe an artifact of the rainbowing issues, or might be the result of the single center tweeter.

Even though there was glaring problems with the kickpanel midrange/ center tweeter, it did some things very well. Everything seemed very coherent and articulate. Next experiment will be with well treated midrange dash pods stuffed in the corners with a center tweeter.


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## I800C0LLECT

Any chance of lowering the the crossover point on your mids? Maybe 400hz? Are you using steep slopes? You could try 24db slopes to see if that helps


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## Orion525iT

I800C0LLECT said:


> Any chance of lowering the the crossover point on your mids? Maybe 400hz? Are you using steep slopes? You could try 24db slopes to see if that helps


I can pretty much do whatever I want. All slopes are 24 db LR.


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## sirbOOm

I fooled with putting two tweeters on the dash of my Silverado about halfway to the A-pillar from center, putting the midranges in the stock locations on the corners by the A-pillar, and midbasses obviously in the door. I REALLY liked how this sounded, but I wanted to make A-pillars and so that's what I did. The tweeters being in the A-pillars resulted in a winder (un-tuned) sound stage but it wasn't significant. I had them crossed at 6,000 Hz. Pioneer Stage 4 gear, FWIW. Firing off windshield pointed straight up.

So, if [ and ] = the A-pillar and C = center of dash. T = tweeter, M = midrange.

[M.............T..........C..........T.............M]


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## Patrick Bateman

sirbOOm said:


> I fooled with putting two tweeters on the dash of my Silverado about halfway to the A-pillar from center, putting the midranges in the stock locations on the corners by the A-pillar, and midbasses obviously in the door. I REALLY liked how this sounded, but I wanted to make A-pillars and so that's what I did. The tweeters being in the A-pillars resulted in a winder (un-tuned) sound stage but it wasn't significant. I had them crossed at 6,000 Hz. Pioneer Stage 4 gear, FWIW. Firing off windshield pointed straight up.
> 
> So, if [ and ] = the A-pillar and C = center of dash. T = tweeter, M = midrange.
> 
> [M.............T..........C..........T.............M]


This is consistent with what I found. 

Basically I tried three things:

With speakers in the corners I get a "hole" in the center

My Genesis has a center channel, but it's not as wide as a stereo setup

This solution, with tweeters in the centre, isnt as wide as stereo, but it's not as narrow as my five channel setup


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## Kazuhiro

whisky22 said:


> just found this with B&W speakers


Is that a yellow mid I see in the front of the passenger door? Arent the mids up behind the silver grill


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## Patrick Bateman

Kazuhiro said:


> Is that a yellow mid I see in the front of the passenger door? Arent the mids up behind the silver grill


Nice catch!










I'm not 100% sure, but it DOES appear that they have the following:

1) stereo midbasses in the lower doors
2) stereo midranges in the middle of the doors
3) mono tweeter where the center channe would normally be

There may well be some speakers we're missing.
Or there may not.

I've found this setup works surprisingly well, particularly if you have a system with a 'hole' in the center of the soundstage. The mono tweeter fills in the hole, pushes back the soundstage, and avoids the problem we always have in the car, where the soundstage pulls towards the driver.


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## Patrick Bateman

bummer, did some googling and found that it's a plain ol' center channel, with a hidden woofer in the dash


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## Kazuhiro

Thats ashame, though I'd still love to hear the system.


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## Patrick Bateman

I found a "better" way to do this with MiniDSP.

The "obvious" solution is to use the MiniDSP center channel plugin. The thing that sucks about that plugin is that it only has two outputs, and they're both mono. Due to this, you have to use a mess of splitters, and more than likely you'll need two MiniDSPs if you go this route. (One for the stereo signal, one for the center channel.)

But - there's a better way!










The plain ol' MiniDSP 2x4 Advanced plugin can do a mono center channel! I didn't realize this until today. Basically you 'turn on' both the left and the right input on one of the outputs, and *voila*, you've got a mono output.

This is really cool, because it means you can do the following:

1) You could have the left mid and the right midrange in stereo, the tweeter in mono, and the sub in mono
2) You could also do a six channel set up, using a splitter. Mono subs, mono tweeter, stereo midrange and stereo midbass. To go this route, you'd have to passively crossover the midrange to midbass, or add another processor.


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## whisky22

Patrick, frequency still 5k+ in theory?


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## Patrick Bateman

whisky22 said:


> Patrick, frequency still 5k+ in theory?


You could use any frequency you want, the main reason that I only use the top two octaves is because the lower in frequency you go, the more that phase matters.

IE, if you ran it all the way down to 1000hz, there's significant phase cues, and those phase cues are going to tell you that the sound is coming from the center.

If you limit yourself to the top octave (10,000hz-20,000hz) or the top two octaves (5,000hz-20,000hz) then your imaging cues are dominated by amplitude.

And amplitude is easy to fix; phase is very very difficult to fix.

This is really easy to experiment with, try running one tweeter in mono with various crossover frequencies and slopes and you'll understand what I mean in a matter of minutes. In my experience, a high xover and steep slopes worked the best, but ymmv.


There's a number of things I like about running one tweeter in mono:

1) If you run a measurement of stereo tweeters, you'll see that there's massive comb filtering from the interference between the two tweeters. You won't see the interference unless you do the measurement in stereo, basically the left tweeter screws up the right tweeters response, and vice versa.
2) I find that a mono tweeter placed in the center seems to 'solidify' the center image a bit.
3) The obvious thing is that it simplfies the setup of the left and right speakers. It's a lot easier to get things to work when you're only trying to play up to 5000hz, instead of 20,000hz. There are hundreds of speakers that will play to 5000hz, there aren't many that will play to 20khz. Basically running a mono tweeter simplifies the transition from midrange to tweeter. You'd think it would sound 'detached' but it doesn't.


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## ANDRESVELASCO

I just will leave this here:

http://www.stereolith.ch/site/pages/index.php?vBloc=2&vPage=6



So... Which was the general consensus here? Single mono (summed L+R) tweeter at center dash will works?


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