# Crazy Imaging in a Stock System



## Patrick Bateman (Sep 11, 2006)

I've been driving around in a rental car today, and stumbled across a really interesting phenomenon. Basically I was listening to some tunes and noticed that *the imaging in this rental car is incredibly precise.* On some tracks the center was floating at eye level, and when there were a number of sources in the soundstage, there was real seperation between all of them.

It was kind of startling! Even a lot of big buck systems can't do this.

I decided to try and figure out how they were pulling this off, and went looking for the speakers. The first thing I noticed was that I had to physically LOOK for the speakers; basically the soundstaging was so good that it wasn't immediately obvious where the speakers were. (IE, you couldn't close your eyes and point to where the sounds were coming from.)

After looking at the car door, it appeared that Vokswagen may have seen the Philips OPSODIS paper. Basically the front stage is a three way, set up like this:

1) tweeters in the a-pillars
2) midranges about 25cm away, a bit closer to the listener and a bit lower in height
3) most interestingly, the midbasses are basically at hip level! Much much closer than you'd typically see in most cars.

It basically mirrors the OPSODIS setup from the Philips paper:


































Here's some pics from the rental car in question, a 2013 Volkswagen Jetta. We see some neat features for soundstaging:

1) OPSODIS style speaker setup, with low frequencies basically emanating from 90 degrees off axis, midrange at about 45 degrees off axis, and high frequencies about 30 degrees off axis
2) Using the entire door for a loudspeaker allows for some epic midbass... You could probably use a ten or even a twelve if you used the same location as Volkswagen
3) I think the door looks pretty sharp! Definitely cleaner looking than anything I've ever come up with 
4) The tweeter pods use a roundover to reduce diffraction. Slick!









Here's what the 2012 car looked like... You can see that the 2012 Jetta uses an 'old-school' speaker set up, with midbass in the lower half of the door and tweeters in the A Pillar. As I see it, the big problem with a setup like that is that it's really hard to get two speakers to blend when they're seperated by two or even three wavelengths at the crossover frequency. (With a crossover of 2khz and a center to center spacing of 21", the mid and tweet are three wavelengths apart in the 2012 Jetta.)


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## Patrick Bateman (Sep 11, 2006)

I mentioned the OPSODIS paper, but failed to explain what OPSODIS is, how it works, or link to the paper.

I couldn't find the paper online, but *here's a quick summary of how this novel arrangement works:*

Basically our perception of low frequencies is phase dependent. For instance, 500hz is 68cm long. That's much much bigger than our ears or our heads, and due to that, the only way that our brain can localize these sounds is by measuring the difference in phase between the left ear and the right ear.

Here's an example of this. Let's say that you're walking down the sidewalk and a car is passing you to the left. The way that your brain can tell that the car is to your left is by measuring the time difference between when the sound hits your left ear and hits your right ear. If your head is 34cm wide and the sound is immediately to your left, then there will be a delay of 1 millisecond between the time that the sound hits your left ear then hits your right. (Sound travels 34 centimeters in one millisecond.)
If your head is 30cm wide then the same angle would require 0.88 milliseconds, again using the same math.

*This is how we perceive low frequencies - it's based on phase.*


Something interesting happens as sounds get closer and closer to directly in front of us - we basically have a 'blind spot.' For instance, if a sound is directly in front of us, there is zero delay between the left and the right ear. The sound hits both ears at exactly the same time. If you've ever noticed that you look around a room to locate a sound, this is part of the reason why. You're not just *looking* for the sound; you're also sampling the sound's location from various locations, which helps you pinpoint it's location aurally.



Due to this 'blindspot', the OPSODIS arrangement is an intersting way to maximize our perception of width. Basically the closer the low frequencies are to your left and your right, the better your ear is at perceiving where they are. Your maximum perception is immediately to your left and to your right, and the minimum is when the low frequencies are directly in front of you. Everything between those two locations are points on a spectrum, but if all of this makes sense, you'll realize that putting low frequencies in the kick panels or in the front of the doors can hurt your ability to pinpoint low frequencies in the soundstage.


Interesting, no?









Here's a crude drawing that I made to illustrate this.

The car at the top is an OPSODIS car, with midbasses to your left and to your right. *Sound radiates in rings, like ripples on a pond.* Our perception of soundstage location is dictated by the difference in arrival between the two ears. In the OPSODIS arrangement, notice that the gap between the waves is quite large. The yellow peaks in the wave have a big fat separation from the red dips in the wave, due to the geometry.

Now look at the conventional setup, pictured at the bottom. See how there's virtually no separation between the peaks and the dips in the wave? See how the yellow peaks in the wave almost hit both ears simultaneously? The effect of that is that your brain will have very little information to separate the left channel from the right, and vice versa.

And this has nothing to do with the size of the speaker or the brand or what the cone is mad of. It's just geometry; the closer that the speakers are to 9 o'clock, the higher the separation between the left and the right. The closer that the speakers are to 12 o'clock, the lower the separation.


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## Dodslobber (Jan 3, 2013)

Very interesting, and very cool. Thanks for this post.


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## asawendo (Nov 22, 2009)

Hmmm maybe this thread is the explaination why I got almost perfect imaging in my current computer audio setup by using 9 o'clock and 3 o'clock speaker position beside me. I do this by coincidence because of the limited space. 

To tell the truth I didn't know before the opsodis arrangement. I'm only using small fullrange 3 inch (audience A3) speakers. At first I try at 10 and 2 o'clock position only to find the opsodis arrangement work the best. The sound almost imaging like my headphone (Sennheiser HD600) but surprisingly with much much better staging.


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## asawendo (Nov 22, 2009)

After reading this thread I try to simulate the opsodis arrangement by using tweeter just in front of me (at my LCD monitor).


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## Patrick Bateman (Sep 11, 2006)

asawendo said:


> Hmmm maybe this thread is the explaination why I got almost perfect imaging in my current computer audio setup by using 9 o'clock and 3 o'clock speaker position beside me. I do this by coincidence because of the limited space.
> 
> To tell the truth I didn't know before the opsodis arrangement. I'm only using small fullrange 3 inch (audience A3) speakers. At first I try at 10 and 2 o'clock position only to find the opsodis arrangement work the best. The sound almost imaging like my headphone (Sennheiser HD600) but surprisingly with much much better staging.


The comparison to headphones is similar to what I'm hearing in this Jetta. Last night I did a couple hours of critical listening, and here's some things I noticed about the setup:

*The Bad:*

First off, VM doesn't have a perfect OPSODIS setup. Basically if it were perfect, the tweeters would be in front of you, the mids would be seperated by ten or fifteen degrees, and the midbasses would be clear to your left and right. Due to the fact that the tweeters are NOT in front of you, I noticed that the soundstage would sometimes be weighted towards the driver side door. Using the balance knob helped a bit, but it wasn't possible to get the type of strong center image that my Genesis has... But my Genesis is a five channel system with a center channel. And the Jetta has waaaaaaaay more width in the soundstage. (IMHO center channels tend to make the sound stage sound narrower.)
A few years back I had Unity horns up on my dash, and the first thing I noticed was that 80% of the music out there simply has no soundstaging whatsoever. A lot of the music I listen to is basically mono. (I listen to a lot of Indie and EDM music.) So even though the system was *capable* of great imaging, there was nothing in the recording. I noticed that a lot last night; a lot of my music just has no real imaging. (This is also one of the reasons I like horns so much; a good horn has great dynamics and great intelligibility, and even bad recordings can benefit from improvements in that area, whereas a mono recording will still sound mono on even the greatest speakers.)

*aaaand The Good:*

Some recordings had a huuuuuuge soundstage, maybe the biggest I've ever heard in a car! For instance I listened to a minimally miked recording of a stage play, and the soundstage seemed like it extended in a circle from my left shoulder to a point all the way to my right, and the actors were spread out in front of me.

This kind of performance was seriously startling; even my Unity horns didn't have a stage that extended to my shoulders; their stage basically went from one side of the car to the other, but *my best systems didn't have that feeling of 'envelopment.'*
Most of my projects have the mids and the tweets very close together, sometimes as close as five centimeters. I've found that this improves intelligibility; as you can imagine it's easier to integrate two drivers when they're separated by just a few centimeters.
Oddly enough, *the Jetta has very good articulation.* I'm a bit mystified by this, as the mids and the tweets are separated by about twenty five centimeters. I really have no idea how they pulled this off; typically I'd expect that the articulation would suffer with such a large gap.

Overall, this system has spectacular imaging.

A few years back I tried a couple systems that had *some* elements of OPSODIS, but not all of them. First I tried a system where the midranges were behind the driver, with the tweets in front. That system sounded good, but I ditched it because the imaging tended to wander towards the back on some tracks, and the huge gap between mids and tweets made things sound 'detached.'









A couple years after that, I saw the OPSODIS paper, and tried using two full ranges up on the dash. Surprisingly enough, on tracks with a wide image the soundstage extended beyond the confines of the speakers. But I ditched that setup for a few reasons. First, it had no dynamics, due to very small drivers. Second, I tried using ambio processing to make the soundstaging better, and ambiophonics make the dynamics even worse. (And the small drivers were hardly dynamic to begin with.)

To make a long story short, I think Volkswagen might be on to something here; basically the system in this Jetta has better soundstaging than both of the systems I mention above. And it didn't suffer from ambio's lack of dynamics, because there doesn't appear to be any processing in the Jetta whatsoever. The main flaw with the Jetta is that the tweeters should be in the *middle* of the dash, not the A Pillars. It might be interesting to try that in my Accord, but to do that will require that I go with a four way. (Due to the distance between drivers, you want to use more drivers to cover a larger 'wingspan.')



For people who are curious about OPSODIS, there's about nine pages of material here http://www.diymobileaudio.com/forum...ion/72891-anyone-tried-using-one-tweeter.html
And there's a thread on ambiophonics at diyaudio, and some related material on my old forum here Audio Psychosis • View topic - Ultra Small Midranges


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## Hanatsu (Nov 9, 2010)

Sounds interesting... I'm gonna rebuild my doors. Perhaps I should consider placing the mids in this manner instead. Can I expect an improvment even though midrange/tweeters ain't in optimal position according to this method?

Sent from my Samsung Galaxy 3 via Tapatalk.


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## raresvintea (Sep 17, 2010)

First off all thanks for the explanations.
Second: with a 2 way independent system the image how can be obtained without TA
? Becasue on Audi A4 B6 2003 the sound i can't localize, the midbass is putted right into the door, on my knee, and the tweeter is placed on the door card but i don't know how it's placed. 

What i want is to obtain a better sound qulity in car without Time alligement, because i don't think that the Jetta has a processor with TA. 

From you description what I understand is that midbass is need to be closed from the tweeter and off axis 90 degrees. The tweeter in witch direction is need to be placed, if you put a laser on the tweeters where the axis intersect? In my car midbass is in the right corner of the door and the tweeter in the sail pannel, and i've modified thetweeter and the position and i've forgot the initial position.


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## Fricasseekid (Apr 19, 2011)

Thanks for write up Patrick! 

I may be heading to a VW dealership this week for a test drive! What do you think they will say when I don't actually want to drive the car anywhere?

So does the Jetta have anything in the way of sub bass?


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## asawendo (Nov 22, 2009)

Patrick maybe one of the reason they image like crazy is minimum crosstalk between the midbass driver where the sound from the left driver mostly comes to the left ear and the sound from the right driver comes to the right ear. 

This is just like headphones where there is almost no crosstalk between drivers. Because of that, imaging and intelligibility usually better than most of car audio system. IMHO that is the reason why listening from headphones is more involving experiences for some of us. On the other side most of car audio system is more capable for accurate sound staging than any of headphones system (the stage is in front of you vs the stage is at you).

And Patrick just curious are you already playing some amibiosonic track on that Jetta?


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## thehatedguy (May 4, 2007)

There was a competitor back in the mid 90s using a sort of similar setup in his Mercedes...Nelson Krammer was his name. Car scored very well. I know the guy who built most of it.

That location his where MB had put midbasses for a number of years.


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## Abaddon (Aug 28, 2007)

I'm *VERY* interested in reading the original paper if it can be made available.


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## Patrick Bateman (Sep 11, 2006)

asawendo said:


> Patrick maybe one of the reason they image like crazy is minimum crosstalk between the midbass driver where the sound from the left driver mostly comes to the left ear and the sound from the right driver comes to the right ear.
> 
> This is just like headphones where there is almost no crosstalk between drivers. Because of that, imaging and intelligibility usually better than most of car audio system. IMHO that is the reason why listening from headphones is more involving experiences for some of us. On the other side most of car audio system is more capable for accurate sound staging than any of headphones system (the stage is in front of you vs the stage is at you).
> 
> And Patrick just curious are you already playing some amibiosonic track on that Jetta?


Yes, this is definitely a crosstalk thing.

Here's my take on this -

I've tried doing a 'full' ambio setup. And while the imaging was occasionally eye popping, 80% of the time the ambio processing made no difference in the imaging at all. The reason for this is simple; ambio makes no difference in imaging when the source is mono. *And a lot of popular music is basically mono.*

But while ambio didn't make a difference in *imaging* on these tracks, ambio *always* hurt dynamics.

The reason for this is also simple; ambio processing mixes in an inverse of the opposite signal. For instance, on the left channel ambio mixes in a copy of the right channel, *but inverted and delayed.*

That additional negative signal hurts dynamics, just as it would if you had a stereo speaker with one speaker that was out-of-phase.



Long story short - this is one of the reasons I think the OPSODIS layout is promising, but *without* the processing. It gives you a compromise between a traditional stereo setup and an ambio setup. You get some of the extra width of ambio, but without losing dynamics. (Since we're not mixing in an inverted signal.)


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## Patrick Bateman (Sep 11, 2006)

asawendo said:


> Hmmm maybe this thread is the explaination why I got almost perfect imaging in my current computer audio setup by using 9 o'clock and 3 o'clock speaker position beside me. I do this by coincidence because of the limited space.
> 
> To tell the truth I didn't know before the opsodis arrangement. I'm only using small fullrange 3 inch (audience A3) speakers. At first I try at 10 and 2 o'clock position only to find the opsodis arrangement work the best. The sound almost imaging like my headphone (Sennheiser HD600) but surprisingly with much much better staging.


If you want to see a silly computer audio setup, stay tuned for my summer project 









What I want to do is build a computer desk with two monitors. The weird part is that I want to use a mirror to reflect the image.









This is the same trick that was used for the Tupac hologram at Coachella a couple years back.


















It's also the same trick that's used in the X-Men arcade game. (Ninja Warriors did this too.) They used mirrors to create a seamless blend between multiple monitors, because there weren't any displays that big back in 1992.

Now here's the ultra-weird part. *I want to use the reflective surfaces to form a horn.* So basically the mirror will reflect the light, and the mirror will also control the directivity of the horn. You'll basically be sitting in front of a giant horn loudspeaker, which also happens to be a computer desk. It'll look a lot like this:









View topic - A true zero-bezel widescreen setup (mirror box) | WSGF

Should be fun


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## req (Aug 4, 2007)

what would be REAL cool, is to make a prototype "car" made from wood and such - and put the speakers in the car (in little pods) and get it all to sound right.

i dont have the money or space to do this... but it seems like having a "test bench" like this would be very useful...

and pat, imagine if you could put monitors in the dash of the car facing up, and using the windshield as the reflector for the image\HUD. then recording some kind of thing where you walk around talking, and based on the speaker placement - the image follows the audio image perfectly around the windshield.

now that would be totally ****ing rad.


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## quietfly (Mar 23, 2011)

This is a great write up... i would also love to see the original article.


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## Patrick Bateman (Sep 11, 2006)

req said:


> what would be REAL cool, is to make a prototype "car" made from wood and such - and put the speakers in the car (in little pods) and get it all to sound right.
> 
> i dont have the money or space to do this... but it seems like having a "test bench" like this would be very useful...
> 
> ...


True!

About a year back I wanted to build a home office into a trailer.
I posted a thread about it on here somewhere.

Basically the idea is that I could have a crazy setup for working in front of the computer, and I could actually use it even if I wasn't home. (For instance, I could just hitch the thing to my car, drive my 'trailer office' to the beach, then work from there.)

Obviously, I'm always looking for an excuse to build stuff


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## quietfly (Mar 23, 2011)

Patrick Bateman said:


> True!
> 
> About a year back I wanted to build a home office into a trailer.
> I posted a thread about it on here somewhere.
> ...


That would be insane... the travel channel had a show about high end RV's there are some RV's that are like mini office buildings 2 full stories and everything you could ever imagine to make a home away from home, although they ran in the millions....

getting back on topic, could you explain how you'd keep stereo desperation with the tweeters so close together?

the picture shows them at ~ 6 degrees almost dead center to the driver....


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## BigAl205 (May 20, 2009)

In post #3, this guy had some interesting test results
360 deg. Sound Reproduction


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## CDT FAN (Jul 25, 2012)

Subscribed.


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## asawendo (Nov 22, 2009)

Getting more and more interesting. I found this on my searching for Opsodis hifi-advice.com - Sherwood S-9 Soundbar

I think my Yamaha is using the similar technology for their soundbar. The sound is coming from outside boundaries of the farthest driver.

And Patrick you are right lots of recordings don't have strong image. So the result is vary from one another. That's poor. But I find several Disney song recording in beautiful image (and that's not audiophile recording).


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## Patrick Bateman (Sep 11, 2006)

quietfly said:


> That would be insane... the travel channel had a show about high end RV's there are some RV's that are like mini office buildings 2 full stories and everything you could ever imagine to make a home away from home, although they ran in the millions....
> 
> getting back on topic, could you explain how you'd keep stereo desperation with the tweeters so close together?
> 
> the picture shows them at ~ 6 degrees almost dead center to the driver....


Yes, that's the big trick, and why OPSODIS works so unexpectedly well.
At high frequencies our perception of location is purely based on INTENSITY.

For instance, if the intensity of the sound slooooowly fades from the left then to the right, you'll perceive that the sound is moving from the left to the right.

BUT -

The same trick doesn't work at low frequencies. And this is because the wavelengths are so long. At low frequencies, it's all phase. You perceive location by the phase of the wavelength.

So...

That's why two tweeters can be very close together, and still give the impression of sound fading from left to right. As long as the intensity is correct, the actual location doesn't matter.

Obviously, this is complicated by comb filtering, but tweeters are very directional, and comb filtering is less of a problem with drivers that have high direcitvity.


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## CDT FAN (Jul 25, 2012)

"As long as the intensity is correct, the actual location doesn't matter."

I am having a lot of trouble following the theories. If it is the intensity is what matters, then is seems to me that it would help the perceived separation when the tweeters were farther apart. That way, the intensity would be greater on each end of the stage and make it wider. If the tweeters are close together, how are your ears going to be able to tell the left from right?


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## montyburns (Jan 3, 2006)

Patrick Bateman said:


> Obviously, this is complicated by comb filtering, but tweeters are very directional, and comb filtering is less of a problem with drivers that have high direcitvity.


I'm a little confused as to how the directional high frequencies are interacting with the wide dispersion of a dome. 

Is 'high directivity of a driver' referring to the directional frequencies being played by it? 

thanks


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## req (Aug 4, 2007)

heck. i am thinking of trying this out.

i have some midranges and tweeters and an extra pair of exodus anarchies lol.

i just need to get my arc audio ps8 back, build\buy some cheap boxes for the anarchies, use the PS8 for settings, use my emotiva UPA-7 ([email protected]) for the amp, and build a little mock up in my living room over a weekend.

what would be really cool is to build a replica of a car interior out of cardboard lol.


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## SPLEclipse (Aug 17, 2012)

Could you bust out the measuring tape and give us some PLDs for those midbass? You said there's no active processing in this system correct? I mounted my midbass as far away and wide as I could get, and t/a changes seem to have a major effect on my midbass response. I'm still not where I want to be with it though.

My car is set up pretty perfectly for this, and in fact I tried center mounted tweets but just couldn't get past the narrowed soundstage. It seems like I might just be biased from listening to "traditional" systems for so long.


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## dynaudiofile (Jun 8, 2013)

Just out of curiosity, did the rental car have a Dynaudio system in it??


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## asawendo (Nov 22, 2009)

dynaudiofile said:


> Just out of curiosity, did the rental car have a Dynaudio system in it??


AFAIK it is equipped with Fender Premium Sound System.


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## mojozoom (Feb 11, 2012)

If it was a Dynaudio system Patrick would have noticed - they plaster the logo over everything and it even comes up on the splash screen when you start the headunit.


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## I800C0LLECT (Jan 26, 2009)

Jetta doesn't have the Dynaudio option. Only the "Fender" option


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## Patrick Bateman (Sep 11, 2006)

dynaudiofile said:


> Just out of curiosity, did the rental car have a Dynaudio system in it??


The system is box stock. Just happens to have really clever 'stock' speaker locations.

The drivers themselves are nothing special, and the distortion and lack of bass was audible. But the imaging was excellent.









^^^ For half a minute I considered buying one, but decided to get one of these instead ^^^

Once I'm finished moving to California I hope to come up with a fun system for this car. The rear deck on this car is interesting, you could put a couple of 15s on the deck due to the very deep rear window.


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## I800C0LLECT (Jan 26, 2009)

Is that the new Mazda 6?...diesel?


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## req (Aug 4, 2007)

looks like it.

pat, im about to get a setup in my house to test this speaker configuration (albiet outside of the car) but are there any specific frequencies for the crossover points this works with?


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## mitchjr (Mar 8, 2010)

Subscribe


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## 14642 (May 19, 2008)

Hey Patrick, Did you listen in both front seats? Was the imaging similar?


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## quietfly (Mar 23, 2011)

Two seat imaging is the holy grail ....


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## sqnut (Dec 24, 2009)

Two seat imaging is a compromise


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## quietfly (Mar 23, 2011)

sqnut said:


> Two seat imaging is a compromise


in a car, yes it is....


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## sirbOOm (Jan 24, 2013)

VW (and Hyundai, Kia, BMW, Lexus, MB, some Fords and Audi, for other known examples) pre-program time alignment into some of their stock head units with varying levels of intensity. This is done via computer modeling vs. "in the car, when the car is built" for the most part. You can't change the programming necessarily in the head units that truly have "OEM time alignment". Adjusting balance isn't time alignment, as we all know. The best OEM audio systems also place speakers where they'd best image in that particular vehicle (of course), but that is a lot to ask, especially of GM vehicles, in my experience. I've driven the same Jetta before and I liked it a lot. I did not have the same love for it though - mostly because VW's have gone to crap since they downgraded their interiors and I get really ticked off by that. I can pull out the headlight switch with a twist and a light pull (ridiculous). Anywho, I also like the Kia Optima and BMW 335. The Kia, hampered by its $0.23 speakers, is nonetheless good - wide, fairly well centered. The BMW exemplifies driver's seat time alignment - voices straight in front of me, but it's kind of narrow.


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## 14642 (May 19, 2008)

quietfly said:


> in a car, yes it is....


I disagree.


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## Patrick Bateman (Sep 11, 2006)

Andy Wehmeyer said:


> Hey Patrick, Did you listen in both front seats? Was the imaging similar?


No, I only listened in the driver's seat. I ended up buying a Mazda6, which has a stock system that sounds like crap. I still have the Genesis with the Lexicon system in it, which sounds very good too. In fact, one of my motivations for buying the Mazda was that I don't want to screw with the Lexicon system, it's that good. (The Lexicon system isn't perfect of course; dynamics are lacking and there's no bass. But there's lots of good engineering and it's not 'fatiguing' the way that the Mazda is.)


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## BFYTW (Jul 21, 2012)

Omg..... after reading the OP I had an epiphany.... all those years I thought the Speakerworks GN had midbasses in the rear seat side walls due to room constraints + using such a large driver. If you think about it with the front seats of those GN leaned back your ears would be close to those rear side panels. With the time alignment used and the loaded Horns.....sorry but that car was just incredible for its time period in car audio


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## Patrick Bateman (Sep 11, 2006)

BFYTW said:


> Omg..... after reading the OP I had an epiphany.... all those years I thought the Speakerworks GN had midbasses in the rear seat side walls due to room constraints + using such a large driver. If you think about it with the front seats of those GN leaned back your ears would be close to those rear side panels. With the time alignment used and the loaded Horns.....sorry but that car was just incredible for its time period in car audio


Yep  I don't think the Osodis arrangement was intentional; I think Speakerworks was just trying to use a midbass that could 'keep up' with the fifteens in the back and the Radians up front. But they accidentally stumbled upon an Opsodis layout, by trial and error.

The thing I didn't realize until a few years ago was that the *width* of the midbasses is really important. So the fact that the drivers were mounted on the edge of the car, and not over the deck, makes a difference. I tried something similar to the GN setup using my '01 Accord, and it didn't work as well as it could have because I put the midbasses on the rear deck, which compromises stage width.


































In addition to that, this type of setup works particularly well with coupes, due to crummy legroom in the rear, which 'pushes' the driver further back towards the rear of the car.


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## Deadpool_25 (Apr 2, 2010)

Abaddon said:


> I'm *VERY* interested in reading the original paper if it can be made available.


I doubt it's exactly what you're looking for, but I saw this in the thread BigAl linked. I'm just starting in on it but there seems to be a LOT more info. OPSODIS


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## BowDown (Sep 24, 2009)

Very interesting read. Thanks for posting this up! Now I'm curious to hear a 2013 Jetta.


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## CDT FAN (Jul 25, 2012)

I am thinking about trying to mount move the mibass speakers back from the factory, front, lower part of the front door to the rear part of the door where they will be closer to 180 degrees. I could put them at the bottom or top of the door. Which would be better? It seems like the top would have a better angle, but the PLD would be even greater between left and right.


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## Deadpool_25 (Apr 2, 2010)

CDT FAN said:


> I am thinking about trying to mount move the mibass speakers back from the factory, front, lower part of the front door to the rear part of the door where they will be closer to 180 degrees. I could put them at the bottom or top of the door. Which would be better? It seems like the top would have a better angle, but the PLD would be even greater between left and right.


I will be doing this for sure, but am going low on the door. For a few reasons, I don't think I want speakers as close to my ears as high on the door would put them. /shrug


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## Patrick Bateman (Sep 11, 2006)

CDT FAN said:


> I am thinking about trying to mount move the mibass speakers back from the factory, front, lower part of the front door to the rear part of the door where they will be closer to 180 degrees. I could put them at the bottom or top of the door. Which would be better? It seems like the top would have a better angle, but the PLD would be even greater between left and right.


I'd stick them in a small sealed box, then try both locations.

The main reason that the lower location may be superior is distortion.
For instance, with an xover of 200hz, the wavelengths are so long, the height difference shouldn't be very audible. (200hz is over five feet long, so long that the height shouldn't matter.) But the *harmonics" may be audible; for instance the third harmonic of 600hz may give away the speakers location. So lowering the height may mask the location that's given away by the harmonic distortion.

Or just use a bandpass box like Hanatsu did, that'll kill the harmonics nicely


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## Deadpool_25 (Apr 2, 2010)

So this OPSODIS thing. Getting the midbasses around 180° is doable. Getting the mids in a decent position too. However, is the tweeter positioning reasonable? 6° between them is possible, but wouldn't you want the left tweeter to be left of your left ear? Seems to me, though it's just a total guess, that you'd be better off with the tweeters in the a pillar or something. Yes? No?


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## CDT FAN (Jul 25, 2012)

What XO points should be used?


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## Deadpool_25 (Apr 2, 2010)

In the 3-way + sub system, the paper called for about 100, 600, 4k. It also seemed to suggest steep slopes.


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## CDT FAN (Jul 25, 2012)

Deadpool_25 said:


> In the 3-way + sub system, the paper called for about 100, 600, 4k. It also seemed to suggest steep slopes.


Thanks. I'm blind.


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## Deadpool_25 (Apr 2, 2010)

Reading that whole thing could do that to a person.


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## req (Aug 4, 2007)

thought id post this...


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## labcoat22 (Mar 29, 2009)

well it official picked up a used 2010 JSW TDi as the family road trip car, now can I sneak a stereo build in with my wife noticing hmmm


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## jimmybee1108 (Apr 26, 2011)

Ok. So could this only work in a 3-way front stage? 
Because in my tacoma, there are spaces on the inner door skin to maybe make a baffle and mount a midbass that's roughly hip height. I could then drill holes in the door card and wrap it in speaker cover cloth to not show. Then where the tweeter is in te stock location, mount a midrange in a PVC enclosure, as close to on axis as possible. The mid is about 3 inches under the sail panel and equally as far from the dash. 

Now here's my other idea. I saw the OPs pic with the tweeters in an enclosure in the middle of the dash. What about behind te rearview mirror pointed at the windshield, reflecting off the windshield, hopefully making some dispersion.


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## labcoat22 (Mar 29, 2009)

req said:


> thought id post this...


this makes me think mid base like the JSW, mids in the pillars and tweats in the middle of the dash like PB' did with wide banders

R-


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## req (Aug 4, 2007)

i was thinking more in the center of the dash at sort of an angle facing the listener (driver) and have the left tweet\mid reflect off the driver side window... dont really know until you put all the stuff in the car and test with it.


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## Regus (Feb 1, 2011)

I'm considering experimenting with this arrangement, but with a twist. For the tweeters I may try using the empty single DIN slot below the head unit (or above if I move it down ), which I've wanted to find a use for ever since I changed from the factory double DIN unit to an aftermarket single DIN unit. I'm thinking I should be able to fabricate a cut-down version of the dash-mounted tweeters in post #6. The big advantage I see is keeping the separation between the tweeters small as per the OPSODIS diagram without having to worry about dash/windscreen reflections that you get from dash mounted speaker. I would of cause be limited to the single DIN height in terms of incorporating a conical waveguide to control directivity but I could still incorporate the PVC pipe to help with diffraction. Before I go any further with this is there anything fundamental I may have overlooked?


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## Deadpool_25 (Apr 2, 2010)

Ok this is just my very uneducated opinion, but I think it's probably a bad idea to use the centered tweeter element in a car. The OPSODIS paper says you should have the tweeters somewhat centered but, and I think this is significant, the left tweeter is still left of the center of your head. This would allow you to locate those high frequencies coming from left or right. If you center the tweeters in a car, all the highs will be coming from your physical right side. Less than ideal IMO. 

I was thinking that in a car, to get as close as reasonable to an OPSODIS setup (without completely ignoring the passenger), you'd want the left tweeter 6° left of the center of the driver's head and the right tweeter as far from the right a-pillar as the left tweeter is from the left a-pillar (which would probably be 6° right of the passenger's head center).

Am I making sense, or crazy?


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## subwoofery (Nov 9, 2008)

Deadpool_25 said:


> Ok this is just my very uneducated opinion, but I think it's probably a bad idea to use the centered tweeter element in a car. The OPSODIS paper says you should have the tweeters somewhat centered but, and I think this is significant, the left tweeter is still left of the center of your head. This would allow you to locate those high frequencies coming from left or right. If you center the tweeters in a car, all the highs will be coming from your physical right side. Less than ideal IMO.
> 
> I was thinking that in a car, to get as close as reasonable to an OPSODIS setup (without completely ignoring the passenger), you'd want the left tweeter 6° left of the center of the driver's head and the right tweeter as far from the right a-pillar as the left tweeter is from the left a-pillar (which would probably be 6° right of the passenger's head center).
> 
> Am I making sense, or crazy?


http://www.diymobileaudio.com/forum...ion/72891-anyone-tried-using-one-tweeter.html 

Kelvin


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## calebkhill (Jan 12, 2013)

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


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## req (Aug 4, 2007)

so basically - if this was a center seat drive car - it will work beautifully lol.

anyone have a mclaren f1 theyd like to play with? LOL


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## Patrick Bateman (Sep 11, 2006)

calebkhill said:


> 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


just posted some ramblings on this here:

http://www.diymobileaudio.com/forum/1959529-post210.html


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## MetricMuscle (Sep 16, 2013)

Is there anything to be gained by mounting just the mid-bass drivers in the OPSODIS location but not the mid and tweeter(s)? My doors just so happen to have a nice large open space right next to my hip but I'm not considering mounting the mid and tweeter on the dash directly in front of me. Is all lost if it's not all done together?


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## cajunner (Apr 13, 2007)

it seems to me that the key part of Opsodis is the far left/right of the midbass frequencies.

As long as you cross the bass higher than the Schroeder frequency of the car and get into the range of those instruments that are inherently playing to the left and right of the center of the stage, you'll buy width and expand the stage to outside of the doors.

The mids being forward and up higher where you can have them sync in the center is also good for your vocal region, and the orchestral centering of instruments that add intelligibility to the mix.

I think the tweeters are in such a reflective environment as a true Opsodis locale is in the dash between the windshield, it won't be right no matter how you angle or distance them.


A modified Opsodis arrangement is probably as good as it gets in the car, and especially as a one-seater focus point.


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## MetricMuscle (Sep 16, 2013)

It will be set up for driver's seat listening position.
I will have T/A and EQ.
What frequency range should they cover or how do I go about determining the Schroeder frequency of my car?

It would seem that previous discussion of this above assumed that the mid and tweeter would be farther away from the listener as in a home environment. The dash would need to be pretty deep to get enough separation. Either way, my dash is not deep nor flat in front of the driver, the shape doesn't really encourage the arrangement.

A 6.5" mid-bass driver is about as large as I'll be able to fit. What specs make for a good mid-bass driver mounted OPSODISly? I have two pair of TangBand W6-1139SB which can dig pretty low and extend up into the 300Hz range pretty well but is really more of a sub-woofer. Depth could also be an issue.


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## robtr8 (Dec 6, 2011)

sub'd, very interested in following this.

That B&W setup looked awsome but it has zero WAF.


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## Hanatsu (Nov 9, 2010)

You determine the shroeder frequency by doing acoustic measurements. Do several measurements around the listening area. The frequencies above the 'SF' will vary in a greater degree as you move the mic. This should be around 250-350Hz.

Sent from my Samsung Galaxy 3 via Tapatalk.


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## 14642 (May 19, 2008)

The tweeters in the center of the dash aren't going to work very well because the reflections off the dash and windshield create MANY tweeters.


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## Regus (Feb 1, 2011)

I've just looked through the OpSoDis paper and there is mention of a low frequency limit of 300 to 400 Hz for the ideal system - this point varies for the various examples given for discrete drivers. Interestingly, it seems that the midbass drivers could be allowed to play down into the sub-bass region, if capable of doing so, rather than be limited to midbass frequencies only.


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## MetricMuscle (Sep 16, 2013)

robtr8 said:


> That B&W setup looked awesome but it has zero WAF.


So often the case but alot more could be done to make it more integrated to the room.



Hanatsu said:


> You determine the shroeder frequency by doing acoustic measurements. Do several measurements around the listening area. The frequencies above the 'SF' will vary in a greater degree as you move the mic. This should be around 250-350Hz.


I'd wanna keep them in the 80Hz to 300Hz range or even let them extend down as low as they are comfortable to assist with the sub duties and provide that multiple sub-woofer location approach.



Andy Wehmeyer said:


> The tweeters in the center of the dash aren't going to work very well because the reflections off the dash and windshield create MANY tweeters.


All the more reason not to attempt it. Even if there was no downside, I'd probably only make a temporary set up to experience it, don't wanna have that mess all over the dash.

The back seat might be a better location to try it, like mounted to the back of the front seats. Would probably really degrade the rest of the presentation but the dimensions would be better and less reflections.



Regus said:


> I've just looked through the OpSoDis paper and there is mention of a low frequency limit of 300 to 400 Hz for the ideal system - this point varies for the various examples given for discrete drivers. Interestingly, it seems that the midbass drivers could be allowed to play down into the sub-bass region, if capable of doing so, rather than be limited to midbass frequencies only.


What is the mid-bass frequency officially, 80Hz to 300Hz, give or take? A small diameter sub-woofer can usually play well above 80Hz and some mid-bass drivers are capable of extending well into sub-bass territory. The spot I'd like to mount on my doors does not provide any room for an enclosure so that would probably be the biggest limiting factor to how low they will go below 80Hz.


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## Regus (Feb 1, 2011)

lycan said:


> We gotta start with some definitions. And what better place to start than a definition of MIDBASS. For the purposes of this thread, we're gonna use :
> 
> 1. higher in frequency than the "pressure zone" of the car. This means wavelengths SHORTER than the interior dimensions of a vehicle.
> 
> ...


That's what Lycan said and who am I to argue?

I mentioned in another thread that I was thinking about midbass drivers in an OpSoDis alignment for my new car's install - it would require some fabrication of mounting points and work on the door card for conventional drivers. Ideally I'd like to adopt the same approach of playing below 80Hz, but this would either require an enclosure or some major sound deadening to get it to work, and I'm still deciding whether I want to go this route or not.


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## req (Aug 4, 2007)

just want to let you all know i did a little test in my house, and *the midbass mounted wide like this was LOADS better at left\right imaging cues than when they were mounted on-axis with the other drivers.*

tweeters in the middle was great for focus of a center - but all the far left\right cues on the iasca CD that were higher frequencies were locked on the tweeters and i could hear them a bit in the midrange and it was really strange. but when i pushed the tweeters out wide with the midranges like a studio monitor orientation, the center image got bloated.

maybe it was lack of EQ and tuning (it was a test setup), but we put a center channel tweeter in there and the focus sharpend right up. it was real nice. 

ive got pictures of the setup - but my computer at work (military owned so no updates) still uses IE8 and cant load my google+ account because google dropped support for this browser completly lol.


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## MetricMuscle (Sep 16, 2013)

Regus said:


> That's what Lycan said and who am I to argue?
> 
> I mentioned in another thread that I was thinking about midbass drivers in an OpSoDis alignment for my new car's install - it would require some fabrication of mounting points and work on the door card for conventional drivers. Ideally I'd like to adopt the same approach of playing below 80Hz, but this would either require an enclosure or some major sound deadening to get it to work, and I'm still deciding whether I want to go this route or not.


I miss his posts and great information he brought to this board.



req said:


> just want to let you all know i did a little test in my house, and *the midbass mounted wide like this was LOADS better at left\right imaging cues than when they were mounted on-axis with the other drivers.*
> 
> tweeters in the middle was great for focus of a center - but all the far left\right cues on the iasca CD that were higher frequencies were locked on the tweeters and i could hear them a bit in the midrange and it was really strange. but when i pushed the tweeters out wide with the midranges like a studio monitor orientation, the center image got bloated.
> 
> ...


What frequency range were the mid-bass covering?
Did you run a sub too? Where was it located?

You tried just a tweeter in the center?
What frequency was it high passed?

Were you using any processing or just keeping the Path Length Differences equal?
How did you integrate the center tweeter?

Do you think the close proximity of a mid-bass driver mounted at hip level on a car door would/could have the same effect with Time Alignment and/or EQ?

I'm not sure I've ever had a woofer mounted that close and aimed directly at my body before. I'll surely feel as much of it as hear it.


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## req (Aug 4, 2007)

i tried several things. if there is something i didnt cover - id be glad to try it again one of these weekends. even specific song(s) i could do as well.

MB______MR__TW_TW__MR______MB

___MB_MR_TW________TW_MR_MB___
MB____MR_TW________TW_MR____MB
MB____MR_TW___TW__TW_MR____MB


_MB_MR_TW_____TW_____TW_MR_MB_
_MB_MR_TW_____________TW_MR_MB_


MB_____MR\TW_______TW\MR______MB <---- if EQ and stuff, this might have been best but the center was kind of unfocused
MB_____MR\TW__TW__TW\MR______MB <--- we liked this the most

and prolly more than that.

but we did all kinds of things. basically every orientation combination we could think of. we had like 10 foot wire runs for each speaker and an open living room. so things like reflections and car-audio based problems would not show themselves unless we got this rig into a car - or a mock-up of a car maybe made of scrap wood or cardboard.

*the bands im going to list are where we tried. *lots of points in between as well. so the midbass we tried the LOWEST point was 250, and the highest crossover we tried was 800hz. the same goes with the rest of the speakers.

the midbass we played from 250~800hz lowpass (exodus anarchy in .5ft^3 w\pollyfill - 5 gallon bucket speaker enclosure LOL)
the midrange was 250~10k bandpass (hi-vi b3s in .5L enclosure)
and the tweet we tried from 2k highpass. (SB Acoustics SB29RDCN-C000-4)

no subwoofer.

we changed them all several times - and only adjusted the level of the speakers. no time alignment or fine EQ was done at all.

we moved the midbass around to simulate being close to the hip on the left and far on the right - and it barely made any difference. while looking forward the midbass' dissapeared. if you turn your head sideways it became very apparent the midbass was there. but who looks at your B pillar while in a car listening to the stereo haha.

the center channel tweeter was assigned as such via the arc audio PS8. i dont know what kind of algorithms are applied to make it work as a center though.

im trying to get some pictures but IE8 is a pain in my ass.


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## MetricMuscle (Sep 16, 2013)

Great info!

Was there a low pass frequency you found the mid-bass to work best with?

How do you like that Hi-Vi B3S? I have a couple pair of them and the B3N. Large magnets, that's for sure.


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## req (Aug 4, 2007)

everything sounded real good with great seperation... we had the midbass playing from i think 300 or 500hz.

we also had a pair of dayton 2" dome midranges (the rs52an iirc). i have had them in a box forever, and one of them sounded cruddy - so we switched to my hi-vi b3s that i built like 10 years ago but never actually used LOL.

as you can see, we played with the height as well as the placement of the speaker to see if things were affected by that. and largely height played the least importance. having the speakers equidistant from the listener and to the sides (midrange+tweeter) was the best (as seen in the last picture) and the fact that they were off axis (as they will be in-car) didnt make a huge difference with the B3S. the aiming of the tweeter (ring radiator) was important, but being that it will be in the pillars, it will be easier to aim.

as far as the midbass, they were very localizable and caused the stage to narrow considerably based on driver location. when forward\outboard with the mid+tweet in the THUMBS DOWN picture toward the bottom, the stage was almost locked to the midbass position.

when moved to 180* as see in the last picture, the stage widened a LOT and the midrange\tweeter was the boundary while the midbass almost dissapeared to the left\right.

my only concern was that when the tweeters were center - the center image was amazingly tight. like a golf ball... but lots of left\right cues that the midrange should have brought wide (like a snare drum that should be far left) was caught right in the middle too. after we put the tweeters wide - the left\right cues were phoenominal - but the center image was bloated in compairason. i dont know if we could have tightened it up using eq and actual tuning - but i think that the left\right information being correct is more important than a bloated center.

here are some pictures.


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## cajunner (Apr 13, 2007)

what recording has a snare drum that is far left?


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## Regus (Feb 1, 2011)

req said:


> when moved to 180* as see in the last picture, the stage widened a LOT and the midrange\tweeter was the boundary while the midbass almost dissapeared to the left\right.
> 
> my only concern was that when the tweeters were center - the center image was amazingly tight. like a golf ball... but lots of left\right cues that the midrange should have brought wide (like a snare drum that should be far left) was caught right in the middle too. after we put the tweeters wide - the left\right cues were phoenominal - but the center image was bloated in compairason. i dont know if we could have tightened it up using eq and actual tuning - but i think that the left\right information being correct is more important than a bloated center.


Really pleased to see that you took the time to do this - I devised a similar setup to yours using my old HT receiver to power midbass, midrange and a single centre channel speakers, but I never got a round to putting it into practice. I only got as far as doing some quick experiments with my HT system comparing stereo with PLII and extreme L/R placement of the front speakers.

Your comments regarding the snare drum have got me wondering again about how to get the best possible centre image. I am intrigued that the steering algorithm in the PS8 seems to be reproducing left/right cues in the centre as well - I don't recall this being an issue with PLII when I did my quick experiments, but may go back and retest things to confirm this.


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## req (Aug 4, 2007)

cajunner said:


> what recording has a snare drum that is far left?


7 drums on iasca test cd. 



Regus said:


> Really pleased to see that you took the time to do this - I devised a similar setup to yours using my old HT receiver to power midbass, midrange and a single centre channel speakers, but I never got a round to putting it into practice. I only got as far as doing some quick experiments with my HT system comparing stereo with PLII and extreme L/R placement of the front speakers.


its tricky when you start adding prologic stuff into the mix. we are talking straight up left\right in car audio ... prologic ii is mainly a 5 channel seperation and steering algorithm. so i dont know how that would work out in regards to opsodis?



Regus said:


> Your comments regarding the snare drum have got me wondering again about how to get the best possible centre image. I am intrigued that the steering algorithm in the PS8 seems to be reproducing left/right cues in the centre as well - I don't recall this being an issue with PLII when I did my quick experiments, but may go back and retest things to confirm this.


i am not saying that the center is reproducing left\right. i am saying when the tweeters are arranged in the center (ala opsodis) that the tweeters physical location is narrowing the stage significantly.

when we put the center tweeter in and assigned it as a center via the ps8 and put the regular left\right tweeters next to the midranges, the stage was as wide (or wider) than the physical speaker locations and the center image was sharper than if there was no center tweeter.

the main track i used to do left\right\center was the iasca sound stage test track with the three voices at left\center\right and the 7 drums.

then i listend to the rest of the cd and noticed that the stage was super narrow with the left\right tweeters (no center channel) aligned 10* from each other in the center. basically when the opsodis tweeter arrangement was used - the stage was ONLY in the center on the higher frequencies. it was also real weird because the midrange was wide, but the highs were all in the middle. i dont know - it didnt work 

*the big thing i took home from the test is that the midbass being left\right of your body works.*


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## namesmeanlittle (Nov 20, 2013)

this is a neat ear trick... you know its a lot easier with two towers in a house.


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## req (Aug 4, 2007)

what?


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## namesmeanlittle (Nov 20, 2013)

i meant with two good towers in a somewhat decently sounding room imaging is not any problem  i am tempted to try this through
loving the 5 gallon boxes that pretty resourceful. i wander what would happen in i put some oversized 80db sensitivity 50 pound mag beast in there, would they crack or violently shader hmm...


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## Nismo (Jan 10, 2010)

If I put tweets (not purchased) into my sail panels, I may be able to wrestle the 3" Faital 3FE22 into the stock tweet location (with some mods), and put the dual Anarchy in the rear of the doors, I'll be pretty close to what you had in the Jetta, Pat.

I REALLY like this idea, and it sounds like the frequencies used were pretty close to what I need to use for my crossover points, anyway.

Eric


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## Patrick Bateman (Sep 11, 2006)

I rented a Ford Mustang last week, and that car (might) have the best center I've ever heard. It is the only car I've ever driven where I was literally putting my head on the center of the dash, trying to figure out if there was a center channel hidden there. One of my cars has a center channel *and the Mustang had a stronger center image than my car*.

It was quite bizarre. If I had to speculate, I'd guess it was due to two things:

1) The Ford uses coaxial speakers. I know that coaxial speakers are generally regarded as being lo-fi, but my Kefs are imaging champs. Also, cheap coaxials generally use a first order crossover on the tweeter and nothing on the midrange, so their 'cheapness' is also very minmalist, and minimalist stereos often image really well.

2) The speakers are mounted up high in the Mustang:

Here's a pic from Crutchfield:











There were lots of problems with the Mustang stereo; it had no bass and the treble wasn't too good. But WOW did it image. It's kind of interesting when you see these really cheap systems image well. I think that going with two and three way systems can improve power handling and it allows you to limit the bandwidth of a driver so that the entire system sounds "clean" and "hifi", but it can also destroy imaging cues at the same time. It's quite a conundrum, because the things we do to reduce distortion can often lead to a soundstage that's completely biased to one side of the car. This is particularly common when you replace a stock full-range or coax with a dedicated midrange and tweeter. With a crossover point at 2khz, the two drivers should ideally be located within 1.75" of each other, and that is only possible with a coax or a very very small midrange and tweeter.


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These fool usually have the kidness to start new threads.


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## MetricMuscle (Sep 16, 2013)

Patrick Bateman said:


> I rented a Ford Mustang last week, and that car (might) have the best center I've ever heard. It is the only car I've ever driven where I was literally putting my head on the center of the dash, trying to figure out if there was a center channel hidden there. One of my cars has a center channel *and the Mustang had a stronger center image than my car*.
> 
> It was quite bizarre. If I had to speculate, I'd guess it was due to two things:
> 
> ...


Picture from Crutchfield, huh? Don't you feel comfortable enough with us to admit you disassembled a rental car to see what it had for audio? We are the only ones who would understand so you can be honest. 

-What model of Mustang or what accessory level do you think it was?
-Do you think it had to have had some sort of TA processing to achieve such a good center?
-Wouldn't equal distance from the listener be essential for a centered image if no TA processing was used?
-How does mounting the speakers up high on the door help?

Of all the home hi-fi rules that car hi-fi breaks, it's the separation of mids and tweeters that amazes me the most. Truncated frames exist so the distance between drivers can be minimized. 
Coaxials definitely get a bad reputation due to such poorly made crossovers on most of them. Are your KEF's the Uni-Q coaxials? Home or in a vehicle?


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## Patrick Bateman (Sep 11, 2006)

MetricMuscle said:


> Picture from Crutchfield, huh? Don't you feel comfortable enough with us to admit you disassembled a rental car to see what it had for audio? We are the only ones who would understand so you can be honest.
> 
> -What model of Mustang or what accessory level do you think it was?
> -Do you think it had to have had some sort of TA processing to achieve such a good center?
> ...



I was wondering if there was time alignment too. The car I was renting was a convertible Mustang from the rental counter at the Vegas airport; I'm guessing the stereo was the base model.

One thing that had me thinking that there might be time alignment was the fact that the image was very well centered on the driver's side, but my passenger didn't notice the same effect. This would be consistent with what I noticed in the Mazda3. In the Mazda3 the soundstage is well centered from the drivers side, but from the passengers side there's no soundstage at all. So I'm guessing that the Mazda3 uses TA biased for the driver's side, and the Mustang might also.

My Kefs are cheap Uni-Q satellites. HT2001 iirc?

As far as mounting the speakers up high, this may have the effect of changing the soundstage because our perception of sound is biased by height. Basically you can fool the ear into thinking that sounds are higher or lower based on the frequency response curve because a lot of our listening cues are based on frequency response. On the flipside of this phenomenon, moving speakers higher can change your perception of the soundstage. (This only applies in the top four octaves from 1250hz to 20khz or 27.2cm to 1.7cm)


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## BowDown (Sep 24, 2009)

My 2010 Fusion had OEM time alignment for driver only. 



Posted from my Samsung Galaxy S III 32gb via tapatalk 2.


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## Hanatsu (Nov 9, 2010)

Patrick Bateman said:


> and minimalist stereos often image really well.


This is my thoughts as well. I've heard cheap computer systems image extremely well using coax or widebanders. 

The stock systems I've heard that image better than others all had the midrange drivers placed high. My theory is that reflection cues from the center console tends to lessen the focus. At least that's ONE of the issues I can think of.


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## Nismo (Jan 10, 2010)

From looking at the settings in the rental Fords I've had, there's a setting for driver, front seat, and all. I believe that's what I was able to cycle through.

Eric


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## MetricMuscle (Sep 16, 2013)

Patrick Bateman said:


> I was wondering if there was time alignment too. The car I was renting was a convertible Mustang from the rental counter at the Vegas airport; I'm guessing the stereo was the base model.
> 
> One thing that had me thinking that there might be time alignment was the fact that the image was very well centered on the driver's side, but my passenger didn't notice the same effect. This would be consistent with what I noticed in the Mazda3. In the Mazda3 the soundstage is well centered from the drivers side, but from the passengers side there's no soundstage at all. So I'm guessing that the Mazda3 uses TA biased for the driver's side, and the Mustang might also.






BowDown said:


> My 2010 Fusion had OEM time alignment for driver only.


Did you sit in the passenger seat too or did you just take the passenger's word for it?
Who exactly was this passenger, what are their HiFi credentials? Would they know good imaging if they heard it?
Sorta makes sense from a sales and marketing standpoint. More likely the person buying the car will check it out from the driver's perspective, not gonna sit in the passenger seat and see how a stereo images. If it sounds alot better than they were expecting sitting in the driver's seat it might give them the warm fuzzy feeling. Not to mention, a soundstage optimized for both front seats is gonna be a compromise and not as good if it was just for one.
I suppose the processor could adjust depending on who was sitting where by using the same input the airbag and seatbelt system uses in the seats to know which is occupied.




Patrick Bateman said:


> As far as mounting the speakers up high, this may have the effect of changing the soundstage because our perception of sound is biased by height. Basically you can fool the ear into thinking that sounds are higher or lower based on the frequency response curve because a lot of our listening cues are based on frequency response. On the flipside of this phenomenon, moving speakers higher can change your perception of the soundstage. (This only applies in the top four octaves from 1250hz to 20khz or 27.2cm to 1.7cm)


I've read some conflicting information on this concept. The whole kick panel mounted philosophy relies on PLD being more important than height. I first read many years ago that the human ear is lots more particular about distances left to right than up and down which is why kick panels give much better imaging.
Then I read recently that the human ear is less particular about height location in only certain frequencies.
Now that TA is so much more popular and easy to get and use, PLD is less of an issue which leaves the kick panel mount option with less appeal. It does provide a location away from glass.




Hanatsu said:


> This is my thoughts as well. I've heard cheap computer systems image extremely well using coax or widebanders.
> 
> The stock systems I've heard that image better than others all had the midrange drivers placed high. My theory is that reflection cues from the center console tends to lessen the focus. At least that's ONE of the issues I can think of.


So, what are the drawbacks to mounting midrange/coaxial drivers higher up on the door?
TA can be handled with a processor.
Would the reflections be greater or fewer?


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## req (Aug 4, 2007)

during the test, i certainly did notice it sounded better with the tweets on top of the mid cabinet and with the midbass inline with my ears 180* from each other as in the pictures.

i would have to do more testing as i only played with all this for a few hours before i put it all back 

but i did come to the conclusion that a coaxial type mount woud most likely be best.


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## BowDown (Sep 24, 2009)

MetricMuscle said:


> Did you sit in the passenger seat too or did you just take the passenger's word for it?


I did in my car.. the image was not as defined as in the driverside. Similar effect to my current 1-seat tune.


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## Rrrrolla (Nov 13, 2008)

I own a 2011 mustang with the shaker 500 system in it. I do recall before I gutted the stereo that (although frequency response was horrible), it did image pretty well. I never once sat in the passenger seat and listened, so I cant comment there. I always wondered if the orientation of the oval mids might have had an effect on the directionality of the higher frequencies, maybe directing them more towards the driver's head and less towards other reflective surfaces. I'm not sure what the directivity patter of a 6X8 speaker actually looks like, but I would THINK it would be the opposite of what I just proposed, being that the cone extends more towards the driver's head making nigher freqencies more "on axis" in that plane. Boy that's a hard one to explain with words...


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## MetricMuscle (Sep 16, 2013)

req said:


> during the test, i certainly did notice it sounded better with the tweets on top of the mid cabinet and *with the midbass inline with my ears 180* from each other* as in the pictures.


One damn minute Admiral! Does the OpSoDis positioning require the mid-bass woofers to be at ear *height* ? As in not down at the bottom rear corner of my doors or is height not an issue? Your bean bag chair seating position had you in roughly the same position as sitting in a car from a height perspective relative to the mid-bass so maybe this isn't an issue at all. The left side will obviously be lots closer to the driver's left ear and more Off-Axis but I doubt being On-Axis would help at mid-bass frequencies anywho.

I'd think at mid-bass frequencies height would not matter but then I never considered the many aspects OpSoDis brings into play. Ear height would be next to impossible in a sedan, maybe in a coupe on the B or C pillar.


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## Hanatsu (Nov 9, 2010)

MetricMuscle said:


> I've read some conflicting information on this concept. The whole kick panel mounted philosophy relies on PLD being more important than height. I first read many years ago that the human ear is lots more particular about distances left to right than up and down which is why kick panels give much better imaging.
> Then I read recently that the human ear is less particular about height location in only certain frequencies.
> Now that TA is so much more popular and easy to get and use, PLD is less of an issue which leaves the kick panel mount option with less appeal. It does provide a location away from glass.
> 
> ...


Physical PLD isn't an issue when you got T/A (one seater). True that height (vertical localization) perception lies in the upper midrange-highs region. In theory you could place a driver that's used below ~2kHz anywhere in the vertical plane and we could still not percieve height cues reliably. This might be true in an anechoic environment, even in a larger, less reflective room... As I said before, reflections cannot be eliminated in a car, it's better to use them to your advantage instead of working around them. Dispersion of a driver is highly proportional to the cone size, unless you use 15" midranges you will have omni-directionality in the (lower) midrange which means the speaker will radiate sound about equally 0-->90deg offaxis. If placed high, the sound will hit the windshield, as long as the reflections "appearent sound source" have the same frequency response as the speaker response we can EQ the reflection along with speaker FR. The windshield will be a source of crosstalk between L/R limiting stage width slightly, the focus however will remain good as long as the the crosstalk is uniform from both leftvand right side. This is NOT the case when you place drivers in kick panels. Your legs and the center console will obstruct the sound which makes the relections from left/right side non-uniform. They cannot be EQed together with the speaker because reflections (phantom sound source) have a different FR than the speaker itself, this will mess up focus, it's possible you might gain better width due to less crosstalk and wider physical placement in the car. Still, bad tradeoff imo.


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## Hanatsu (Nov 9, 2010)

For tweeters though, they will play above the pistonic range in most cases. The reflections can be controlled then, same with the upper octaves of widebanders. Keep those away from the windshield and you'll avoid some issues. 

Sent from my Samsung Galaxy 3 via Tapatalk.


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## Hernan (Jul 9, 2006)

calebkhill said:


> 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


Over the last year i have the woofers at the kick and the tweeters at the dash center 8 inches one from each other. 
No proccesing, It s the best sounding setup I ve found after several weeks work.
They are still there. I ve found this arrengement by trying and error.


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## Hernan (Jul 9, 2006)

Andy Wehmeyer said:


> The tweeters in the center of the dash aren't going to work very well because the reflections off the dash and windshield create MANY tweeters.


I use this setup in an old BMW E30. The dash is very small and it works, if not perfectly, better than other arrengements,


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## req (Aug 4, 2007)

MetricMuscle said:


> One damn minute Admiral! Does the OpSoDis positioning require the mid-bass woofers to be at ear *height* ? As in not down at the bottom rear corner of my doors or is height not an issue? Your bean bag chair seating position had you in roughly the same position as sitting in a car from a height perspective relative to the mid-bass so maybe this isn't an issue at all. The left side will obviously be lots closer to the driver's left ear and more Off-Axis but I doubt being On-Axis would help at mid-bass frequencies anywho.
> 
> I'd think at mid-bass frequencies height would not matter but then I never considered the many aspects OpSoDis brings into play. Ear height would be next to impossible in a sedan, maybe in a coupe on the B or C pillar.


yeah. we tried them at the distances in his sedan using the rear-door speaker locations and it still worked awesome. we tried to mimick the locations with the bean bag chair. im telling you, mounting the midbass like this works awesome.


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## MetricMuscle (Sep 16, 2013)

req said:


> yeah. we tried them at the distances in his sedan using the rear-door speaker locations and it still worked awesome. we tried to mimick the locations with the bean bag chair. im telling you, mounting the midbass like this works awesome.


This is a good thing because the only real spot I'll have for a dedicated mis-bass woofer will be at the lower rear corner of the front door but you are saying that even behind the listener like in the rear door locations sounded good too. That would give me a no-cut option. I like having all these options.

I just looked at the picture again, what about sub-woofer placement up close behind the listener? Anybody try this? Would be easy in a small sportscar like a Miata or such.


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## req (Aug 4, 2007)

i am fairly sure subwoofers are even less important as to the placement and more to do with the phase relationship of the crossover point with the midbass.


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## sqnut (Dec 24, 2009)

I'm guessing a bit here, I haven't tried it to be sure. I think woofers at the sides would work great as dedicated mid bass in a three way, with the mid and tweeter up front. It may give you a perception of a slightly wider stage. But as a two way that location may be less than ideal.


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## Orion525iT (Mar 6, 2011)

req said:


> yeah. we tried them at the distances in his sedan using the rear-door speaker locations and it still worked awesome. we tried to mimick the locations with the bean bag chair. im telling you, mounting the midbass like this works awesome.


To bring more into this, I still wonder how this relates to midbass arrays (aka cone of confusion). I have been considering this for some time. With midbass placement to either side as optimal, there isn't any good way to implement an array. We still have the issue of nulls. So an interesting experiment would be to see if you can get the same results with a set of midbass to the sides and other midbass placed elsewhere. The other question I have is wether you can get the benefit of a wider stage with smaller midbass to the sides and then larger midbasses elsewhere to provide the visceral iimpact and volume needed/desired for midbass. The key issue here is that door mounted midbass has a host of issues, from size limits to rattles.

I might try this at some point, since I already have 8" midbass firmly mounted in my kicks. The doors in my car do not lend themselves to driver placement due to the window regulator mechanism but smaller drivers, like the Dayton ND-91s, would work in the doors mounted around the hip.


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## Orion525iT (Mar 6, 2011)

sqnut said:


> I'm guessing a bit here, I haven't tried it to be sure. I think woofers at the sides would work great as dedicated mid bass in a three way, with the mid and tweeter up front. It may give you a perception of a slightly wider stage. But as a two way that location may be less than ideal.


Without question. 3-way is necessary. But, maybe something similar could be achieved with midbass to the sides and widerangers up front.


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## thehatedguy (May 4, 2007)

How high can you play the midbasses in a setup like that? I can't find too much information about it.

Was thinking about a setup like that and some big body horns.


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## sqnut (Dec 24, 2009)

I wouldn't want them playing anything above ~500hz.


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## cajunner (Apr 13, 2007)

that would be the trick, as always.

getting horns to play from 350 hz on up, and putting mini-subs at the sides.

the only way I can see this happening is with a unity horn style, or using dedicated midrange compression drivers in the front stage on larger horn bodies, and some supertweeter horns up higher.

maybe like, 350 on down to some reasonably high output slim subs, and 350 to 4K running on some special big bodies using 2" exit pro compression drivers, or the cheaper Atlas/Selenium midrange compression drivers, and 4K on up to some ribbon horns in the A Pillars.


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## req (Aug 4, 2007)

i read in one of the opsodis whitepapers that the optimal lowpass crossover point should be less than 800hz for the midbass because the distance between your ears is greater than 1\4 wavelength above that point. this will mess with the phase because the wave from the right will hit the left - and that is the basis of this working.

sorry i dont have a source for that...

i had it about 500hz @ 12db\oct i think. so it would have extended up to about 1000hz ... so i think that 300~400hz would be a good place to start.

we tried the midbass all around, and it was without a doubt the best when they were to the side 180* out of phase, and inline with our ears versus any other situation - ASSUMING IT IS A 3-WAY SYSTEM.


*i would not recommend this with a crossover point higher than 800hz or in a 2-way system.*


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## Regus (Feb 1, 2011)

req said:


> i read in one of the opsodis whitepapers that the optimal lowpass crossover point should be less than 800hz for the midbass because the distance between your ears is greater than 1\4 wavelength above that point. this will mess with the phase because the wave from the right will hit the left - and that is the basis of this working.
> 
> sorry i dont have a source for that...
> 
> ...


Funny you should post this just when I was looking at wavelengths in relation to vehicle dimensions. At 800Hz we're looking at ~17" (if the online calculator I found can be trusted), whereas at 400Hz it increases to ~34" and so on. Whilst a 180 degree alignment at the back of the doors isn't any wider than the front of the doors, if we look at interference between waves radiating from a point source then the pattern of nulls would occur at a different point in relation to the cars width with Opsodis midbass drivers compared to kick or front of door mounted drivers, varying with frequency/wavelength if my physics is still up to scratch (it may not be so feel free to correct anything I've overlooked or got wrong). Reflections are harder to predict but will also play a part in this of course.

My take on this is that while Opsodis won't cure cancellation in the way an array might, it may just shift the nulls to a region of the interior in which we're not going to be listening, especially if the crossover point is kept as low as possible. There is of course the principal benefit of enhanced imaging which alone might be a good enough reason to go with Opsodis.

I wish I had more time to go into the theoretical side of this and see what kind of system design would result but I don't know when I'd be able to. For now I'm probably going to jump ahead to some in-car experiments with a temporary midbass enclosure and see whether any of this translates to the car and if so, how well, then maybe reverse-engineer whatever I find works best to see how and why.


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## cajunner (Apr 13, 2007)

what I was thinking was to make a folded horn for the midrange that had it's exit opening adjacent to the midbass driver, in the doors.

this would accomplish a higher sensitivity for the midrange, allowing a higher output from small cones, and it would allow the door cavity to be used as the enclosure for the mid bass, by themselves. It gets you around the small enclosure cavity penalty, and you can tune it for the "chest/throat resonance" of 150 hz to 300 hz, with the horn contributing at the mid bass speaker's physical location.

I just don't know how many folds, or how large a 5.25" midrange horn would have to be, and if it could be incorporated into the bottom of most door wells, or on the bottoms of the doors. The doors with 36" x 8" x 2" of internal volume or capable outside, would seem large enough to get a decent mid bass wave formation going....

but I'm no acoustical engineer, haha..


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## MetricMuscle (Sep 16, 2013)

sqnut said:


> I'm guessing a bit here, I haven't tried it to be sure. I think woofers at the sides would work great as dedicated mid bass in a three way, with the mid and tweeter up front. It may give you a perception of a slightly wider stage. But as a two way that location may be less than ideal.


In my mind a mid-bass is a driver optimized to cover the area between a sub-woofer and a mid. It allows them to perform better by covering frequencies at the edge of their best performance range. A 2-way is such a compromise to me, you are asking too much of the drivers and stretching them out of their comfort zone. 
A mid-bass is more like a woofer in a typical home hifi 3-way speaker. Woofer covers from around 35Hz up around 300 to 800Hz. Mid covers up around 3,000 to 5,000Hz and a tweeter takes it from there. A subwoofer isn't really necessary for music but gets used in the automotive environment because it's not easy to mount a woofer in a door, dash or kick panel.



Orion525iT said:


> To bring more into this, I still wonder how this relates to *midbass arrays (aka cone of confusion)*. I have been considering this for some time. With midbass placement to either side as optimal, there isn't any good way to implement an array. We still have the issue of nulls. So an interesting experiment would be to see if you can get the same results with a set of midbass to the sides and other midbass placed elsewhere. The other question I have is wether you can get the benefit of a wider stage with smaller midbass to the sides and then larger midbasses elsewhere to provide the visceral iimpact and volume needed/desired for midbass. The key issue here is that door mounted midbass has a host of issues, from size limits to rattles.


I read most of that thread and tried to soak it in. Were you able to figure out exactly where the various drivers would need to be mounted in your car so as to be on/in the cone of confusion?



Orion525iT said:


> I might try this at some point, since I already have 8" midbass firmly mounted in my kicks. The doors in my car do not lend themselves to driver placement due to the window regulator mechanism but smaller drivers, like the Dayton ND-91s, would work in the doors mounted around the hip.


I started a thread to get suggestions for a 5.25" mid-bass driver as that is all I thought I could fit on/in my door. There are some out there but 6.5" seems to be the starting point in most folks mind. 7", 8" 9-10" on up, even better!
Those ND-91 are pretty small unless you were to use multiples all in the OpSoDis location. How about a vertical array running up the door?



Regus said:


> Funny you should post this just when I was looking at wavelengths in relation to vehicle dimensions. At 800Hz we're looking at ~17" (if the online calculator I found can be trusted), whereas at 400Hz it increases to ~34" and so on. Whilst a 180 degree alignment at the back of the doors isn't any wider than the front of the doors, if we look at interference between waves radiating from a point source then the pattern of nulls would occur at a different point in relation to the cars width with Opsodis midbass drivers compared to kick or front of door mounted drivers, varying with frequency/wavelength if my physics is still up to scratch (it may not be so feel free to correct anything I've overlooked or got wrong). Reflections are harder to predict but will also play a part in this of course.
> 
> My take on this is that while Opsodis won't cure cancellation in the way an array might, it may just shift the nulls to a region of the interior in which we're not going to be listening, especially if the crossover point is kept as low as possible. There is of course the principal benefit of enhanced imaging which alone might be a good enough reason to go with Opsodis.
> 
> I wish I had more time to go into the theoretical side of this and see what kind of system design would result but I don't know when I'd be able to. For now I'm probably going to jump ahead to some in-car experiments with a temporary midbass enclosure and see whether any of this translates to the car and if so, how well, then maybe reverse-engineer whatever I find works best to see how and why.


It's interesting to read how different folks are thinking about this and relating it to how they understand and view audio. I don't like the idea of any crossover points between 300Hz and 3,000Hz. If a mid-bass is not located very close to the mid and tweeter then it needs to be low passed no higher than 300Hz and let it cover down into sub territory as far as it is comfortable.

I look forward to hearing how your in-car experiments go.


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## req (Aug 4, 2007)

Regus said:


> Funny you should post this just when I was looking at wavelengths in relation to vehicle dimensions. At 800Hz we're looking at ~17" (if the online calculator I found can be trusted), whereas at 400Hz it increases to ~34" and so on.


i think they were only worried about 1\4 wavelengths IIRC.


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## Zippy (Jul 21, 2013)

A couple of weeks ago I test drove the new 2014 Jeep Cherokee with the upgraded sound system. They have a 6.5' in each of the four doors, a midrange on the dash next to the a pillars, a sub in back, and the tweeters centered on the dash firing towards the glass. The staging was crazy good for a stock system. The mid bass was muddy as all get out, but the staging was great. I think swapping speakers may be enough for that vehicle.


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## Regus (Feb 1, 2011)

req said:


> i think they were only worried about 1\4 wavelengths IIRC.


Good point - I really need to go back through the OPSODIS paper and fully digest the information it contains, but it could take me a while.



Zippy said:


> A couple of weeks ago I test drove the new 2014 Jeep Cherokee with the upgraded sound system. They have a 6.5' in each of the four doors, a midrange on the dash next to the a pillars, a sub in back, and the tweeters centered on the dash firing towards the glass. The staging was crazy good for a stock system. The mid bass was muddy as all get out, but the staging was great. I think swapping speakers may be enough for that vehicle.


I noticed the same thing with the stock system in my new car (2009 Suzuki Swift) with regard to the midbass - there's more output from the rear door speakers but it's boomy whereas the fronts are much clearer but don't play as low. The rears would be close to the ideal OPSODIS alignment for midbass though so I may try using these locations for the midbass drivers and then play around with the front stage and see how much I can improve things using the stock locations before going down the route of installing drivers in other locations.

I'd still like to get away from using the doors though, which is why I'm planning on trying some different combinations of drivers in temporary enclosures to see what works and what doesn't before I fully commit to tearing everything out and starting a proper install.


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## thehatedguy (May 4, 2007)

Aside from being impossible to build- the smaller the speaker, the longer the horn has to be, you really wouldn't want to fold a midrange horn if you didn't have to. The horn would still have to be pretty large for it to work, and you would need a back chamber for the midrange tuned to cancel out the reactance of the horn.

It wouldn't be an easy thing to build.




cajunner said:


> what I was thinking was to make a folded horn for the midrange that had it's exit opening adjacent to the midbass driver, in the doors.
> 
> this would accomplish a higher sensitivity for the midrange, allowing a higher output from small cones, and it would allow the door cavity to be used as the enclosure for the mid bass, by themselves. It gets you around the small enclosure cavity penalty, and you can tune it for the "chest/throat resonance" of 150 hz to 300 hz, with the horn contributing at the mid bass speaker's physical location.
> 
> ...


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## thehatedguy (May 4, 2007)

800 hertz isn't a problem on the big bodies...you could get to 600 with the right drivers, but not much lower. It would be a 2 way unless you added tweeters/super tweeters to it.



req said:


> *i would not recommend this with a crossover point higher than 800hz or in a 2-way system.*


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## MetricMuscle (Sep 16, 2013)

req said:


> i am fairly sure subwoofers are even less important as to the placement and more to do with the phase relationship of the crossover point with the midbass.


Would time alignment be necessary with OpSoDis mid-bass arrangement? Crossover point dependent? Good to have regardless? 

Did you use any TA when you experimented with them in the sedan's rear doors?
What crossover points did you try?


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## cajunner (Apr 13, 2007)

thehatedguy said:


> Aside from being impossible to build- the smaller the speaker, the longer the horn has to be, you really wouldn't want to fold a midrange horn if you didn't have to. The horn would still have to be pretty large for it to work, and you would need a back chamber for the midrange tuned to cancel out the reactance of the horn.
> 
> It wouldn't be an easy thing to build.


perfect for 3D printing with 'scavenged cavity' or whatever they call it, that you go thin shell and fill in with milkshake.

if you have a place in the door that works out for the dimensional attributes for the tuned compression chamber, and you've got at least 60" of length, I mean you're not trying to get it down into 40 hz territory, somewhere between 150 and 225 hz should be possible?

and folding the horn is okay if you're talking about the 400 hz and down, or wherever you could cut off the note-bending.


the horn doesn't have to be very long for midrange frequencies and looking at midrange boxes for PA, the horn is very shallow and they do work some for increasing output...

or you could run the horn out of the sides, for the 350 on down, and let the 5.25" midrange woofers do double duty from higher up in the door.

that might be cool, if the group delay mirrors the increased path length from being further from the ear.


then you'd get Opsodis, with say, a Kef Uni-Q driver in the factory door location for the compression chamber...


minus the tweeter part.


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## Patrick Bateman (Sep 11, 2006)

req said:


> i read in one of the opsodis whitepapers that the optimal lowpass crossover point should be less than 800hz for the midbass because the distance between your ears is greater than 1\4 wavelength above that point. this will mess with the phase because the wave from the right will hit the left - and that is the basis of this working.
> 
> sorry i dont have a source for that...
> 
> ...



That's so cool that this is working for you 

When I tried my pseudo-opsodis think with the two full ranges on the dash and the midbass low and close, I was shocked how the sound seemed to come from where the speakers WEREN'T.

As far as the phase goes, if you have a way to shift it you might try that. In an ideal Opsodis setup the speakers are arrayed in a circle around the listener. But we can't do that in a car, because it's rectangular and we're closer to the left one.

Due to that, a bit of experimentation with delay or a simple phase shift might yield improvements.

For instance:

If your tweeters are 120cm away and your midbass is down by your hip or thigh and the midbass is 60cm away, that's a PLD of 60cm.

With that PLD, we can calculate the phase shift.

With a crossover of 567hz, the PLD between the two speakers is one wavelength. *So the midbass will be in-phase with the tweeter, but it will "lead" by one wavelength."

If you move the xover point up to 850hz, the midbass leads by a wavelength and a half, and it's now out of phase. (Because 850hz is 40cm long, and the sound travels 60cm, so it's one and a half wavelengths.)

Luckily, our perception of phase differences gets worse as frequencies get lower. On the downside, in the two octaves from 250hz to 1000hz we're particularly sensitive to phase shifts. (IE, a phase shift at 60hz is way less audible than a phase shift at 500hz.)

The formula for figuring out the wavelength is (34,000cm per sec / wavelength)

*


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## Patrick Bateman (Sep 11, 2006)

thehatedguy said:


> Aside from being impossible to build- the smaller the speaker, the longer the horn has to be, you really wouldn't want to fold a midrange horn if you didn't have to. The horn would still have to be pretty large for it to work, and you would need a back chamber for the midrange tuned to cancel out the reactance of the horn.
> 
> It wouldn't be an easy thing to build.


Bruce Edgar recommended designs like this, but it's really hard to follow Edgars advice with undersized horns. Basically Edgarhorns are built in a 'textbook' manner.

But you can 'cheat', particularly if you have EQ and DSP.

Of course this is a slippery slope. For instance, if you use reactance annulling to smooth out the response of a horn, it's going to be smooth in the frequency and time domain. If you smooth a horn with EQ, the frequency response will look good but there will still be a resonance in the time domain.

Basically the Edgar solution fixes it physically, the EQ fixes it electronically. The Edgar solution requires a big horn, but it's an optimal solution.

A couple of weeks ago I finished a tapped horn for my living room, and it's response was 'lumpy' because I used an Alpine car sub with a high Q. I dialed out the resonances using an EQ, and I gotta admit, it sounds really good.


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## cajunner (Apr 13, 2007)

what I like about doing a back-loaded horn in the door is it's got everything. 

you need extra output? check.

you need a pro driver to run below Fs? check. Pro drivers, chosen for their output, are ideal horn driver candidates with huge motor strength, light quick cones and low Qts.

you need an enclosure, that isn't ported to the door interior, with increased excursion control? check.

the compression chamber loads the woofer without the severe penalty in midrange bloom and Fc rise of a tiny sealed cavity.

then you have the option of putting the horn exit in the rear of the door, where psychoacoustics presents that magical stage extending well outside of the mirrors....

it kills a lot of birds with one 3D printed stone.

it would be awesome if CAD was used to produce an entire door panel's aesthetics, with the horn wound inside of a homogenized 'beauty panel' where it would be undetected, or perhaps accentuated with accents, that might be interesting too...

sort of how you can see the **** pipe wind around under a toilet, giving away it's secrets.

and something that attaches to the door, in the replacement panel category, would necessarily be an entire enclosure, making up the horn if it's necessary for the volume and length of the horn. 

like a flattened nautilus, wrapping around the high mounted driver and extending to the rear of the door...

maybe form it up using clay mold halves, and getting a working template going.


I wonder what that would sell for on the eplay...


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## Patrick Bateman (Sep 11, 2006)

I think that one of the reasons that tapped horns sound so good is that it's basically like having two speakers playing at the same time, but separated by a delay of one quarter wavelength. So you basically get a variation on the multiple sub approach, *but with one driver.*

I tried some experiments to see if you could use that phenomenon to 'aim' the sub, but found that it's fairly pointless because the wavelengths are so low and the room is so small.

Long story short - 

I think your idea has merit, but these wavelengths are so long, it doesn't really matter where the exit of the horn is. The length of a car cabin is about 140hz, so moving the exit of the horn by half a meter in any direction won't be audible IMHO.

Basically just put the exit where it will fit and enjoy a speaker that behaves a bit like two subs, not one. (Note that ported boxes don't do this, because the bandwidth of the rear wave is a fraction of an octave. In a tapped horn or a back loaded horn or a dipole or a ripole or a cardioid or a U-Frame or a W-Frame the back wave is playing a few octaves of bandwidth.)


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## cajunner (Apr 13, 2007)

because from what I understand, the higher the frequency you are trying to control the waveform, the shorter the horn becomes.

long bass waves require long horns, short midrange/midbass waves, not so much.

or it could be that the horn length and frequency is related to the amplification desired, and 'low and slow' gives the most output....


they can get a 4" Foster to put out 50 hz loud enough to hear it in a room, in a box size small enough to bolt to a truck door. I'm only asking to get down to the Schroeder frequency where the sub makes it's presenting details, in a box size small enough to fit on a car door, where at the most, you're asking for 80 hz or higher.


seems like it could be done.


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## thehatedguy (May 4, 2007)

Wait, are you talking about a back loaded horn or a front horn?


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## thehatedguy (May 4, 2007)

JLH said once he had some tapped horn design that would fit on the lower part of a car door. I'm not smart enough to do a design like that...wonder if he would share it?


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## Patrick Bateman (Sep 11, 2006)

cajunner said:


> because from what I understand, the higher the frequency you are trying to control the waveform, the shorter the horn becomes.
> 
> long bass waves require long horns, short midrange/midbass waves, not so much.
> 
> ...


The length of a horn provides gain, the diameter of a horn controls directivity. For instance, if you put a 1" driver on a 1" tube that's ten feet long, it would load the driver down to about 35hz, *even though the mouth is only 1" in diameter.* (It would also be insanely resonant and horrible sounding; tapering smooths out horns.)

On the flipside of this equation, you could also put that 1" driver in a 90" horn that's 15" wide by 7.5" deep. You'd get directivity control down to 900hz and gain down to about 450hz.

The math for directivity is just the length: (speed of sound / length) or (13,500" per second 15) = 900hz
The math for gain is the same equation, but divided by four. (13,500" per second / 7.5") = 450hz

The second formula gets you in the ballpark; to do a proper sim you need hornresp.


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## cajunner (Apr 13, 2007)

Patrick Bateman said:


> I think that one of the reasons that tapped horns sound so good is that it's basically like having two speakers playing at the same time, but separated by a delay of one quarter wavelength. So you basically get a variation on the multiple sub approach, *but with one driver.*
> 
> I tried some experiments to see if you could use that phenomenon to 'aim' the sub, but found that it's fairly pointless because the wavelengths are so low and the room is so small.
> 
> ...


I believe it would be quite audible since like you say, the horn's back wave is presenting with frequencies at or above 300 hz, and well within the range of being highly localizable.

If you have the horn exit to your 180 degree sides, that produces a 'virtual driver' with the midrange further forward and up in the door, in between the two locations.

OR, exactly where you'd want to bring the "image angle" to make the widest stage possible.

that would be the psychoacoustics at play, and the midrange would dominate above a set frequency (tone-bending) where you'd have that gradual hand-off, and the time delay of the horn, or group delay, would be minimized by the closer driver, leaving the horn exit in phase with the driver at these frequencies that are most image dominant, ie. 1K or so, at an 11" length, it's right in the sweet spot.

this sounds better and better, and I haven't had my coffee today, imagine that....


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## cajunner (Apr 13, 2007)

thehatedguy said:


> Wait, are you talking about a back loaded horn or a front horn?


back loaded horn, using the factory "hole" for a compression chamber. On a door that has high factory locations.

You'd have to get creative with the chamber's compression exit, due to the chance a side-mounted port causes the cone to rock from being forced on unevenly, but besides that, (think hydrodynamics, jet port, angled entrance, etc.)you'd be okay to wind that horn around the driver and bring it to the door's rear, where the exit contributes to each part of OpSoDis, using just the single driver.

Do it with a JBL 2118, and the horn extends for 9 feet around it, that would be a loud door....


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## cajunner (Apr 13, 2007)

Patrick Bateman said:


> The length of a horn provides gain, the diameter of a horn controls directivity. For instance, if you put a 1" driver on a 1" tube that's ten feet long, it would load the driver down to about 35hz, *even though the mouth is only 1" in diameter.* (It would also be insanely resonant and horrible sounding; tapering smooths out horns.)
> 
> On the flipside of this equation, you could also put that 1" driver in a 90" horn that's 15" wide by 7.5" deep. You'd get directivity control down to 900hz and gain down to about 450hz.
> 
> ...


this is the way to figure out the physical dimensions, or feasibility...

which is greatly appreciated.

but I want to believe that it's possible to put an 8" pro driver into a 2" thick nautilus that uses the face of the door for the expansion rate, and provides 6 db of gain in the region of 100 hz to 450 hz, is that so bad?

and follows Opsodis theory, and allows dynamic snare hits to move your uvula involuntarily with your mouth closed...


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## cajunner (Apr 13, 2007)

thehatedguy said:


> JLH said once he had some tapped horn design that would fit on the lower part of a car door. I'm not smart enough to do a design like that...wonder if he would share it?


isn't a tapped horn able to get up into the 350 hz range? That might work if you could put the single fold towards the front of the car door, and the horn exit and driver mount towards the rear of the door, at your side for OpSoDis distribution concerns.

with the gain from the tapped horn, you would no longer be limited by the amount of mid bass available in any given system and good to go for whatever kind of midrange, compression driver on car audio bodies or something else.


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## Patrick Bateman (Sep 11, 2006)

thehatedguy said:


> JLH said once he had some tapped horn design that would fit on the lower part of a car door. I'm not smart enough to do a design like that...wonder if he would share it?


oh they're really easy to do. You could cook one up in hornresp in under an hour. (Tapped horns are fairly hard to screw up, I'd say they're actually quite a bit easier to get right than bandpass or vented boxes, because those two box types get boomy in a hurry if the tuning is off.)






































^^^ here's a few of the tapped horns I built that fit under a dashboard. A lot of them use push-pull to reduce 2nd harmonic distortion. Basically so you can run a small driver hard, without it sounding like crap

JLH used an Eminence Alpha iirc, but I went with Aurasound because of it's low distortion motor and large displacement.









I didn't label my measurements, but iirc, this is a measurement of the frequency response and THD of a B&C 8NDL51 in a small sealed box. (This is the one from my 2001 Accord.) In the measurement we see that the B&C is crazy flat, and low distortion too. It's hard to beat a small sealed box.









IIRC, the top measurement is the dual-aurasound tapped horn vesus the 8NDL51 sealed box, *but measured in-car.* You can see the Aurasound distortion is nearly as low as the 8NDL51, but not quite.

That's basically why I never pursued this any further; the 8NDL51 in a small sealed box gives more output with less hassle. I don't see any reason to run these without an enclosure, as they play plenty low and their power handling is higher in a sealed box.

It wasn't until a few years later that I started to wonder WHY the tapped horns sound good, and I think it's because they mimic the effect of multiple subs.

If that is the case, then any of the open back speaker types will work. You could even go dipole.

Then again, it's only a theory, so who knows? I'm running dipole for the midbasses on my current speaker, but I'm running sealed *and* tapped horns for the bass. (My current setup uses four subwoofers, and half are sealed.)

But, yeah, dipole midbass seems to work nicely. The other variations might work nice too. (Tapped horn, back loaded horn, dipole, cardioid, u-frame, w-frame, H-Frame, ripole, etc.)

Actually my midbasses are technically a cardioid, not a dipole.

All of these enclosure types are variations on the same thing, the only difference between them is the volume and length of the rear chamber. A dipole has a rear chamber that's virtually non-existent whereas a BLH has a rear chamber that can be a few meters long.


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## Patrick Bateman (Sep 11, 2006)

If anyone is wondering why the distortion on the B&C is so high in the first measurement, turns out I measured at 10watts. Here's the post:

Critique my 8" Pro Audio Woofer 8" Waveguide / Compression Driver Plans - diyAudio

Gotta love google image search! Just pop in my own measurement and let Google figure out what the heck it is.

The B&Cs were almost deafening with 10 watts. I remember doing the measurement in my drive way and it was LOUD. It's hard to appreciate how little power is needed to get loud at 1000hz.


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## req (Aug 4, 2007)

thehatedguy said:


> 800 hertz isn't a problem on the big bodies...you could get to 600 with the right drivers, but not much lower. It would be a 2 way unless you added tweeters/super tweeters to it.


what i mean is for a normal 3 way system with midbass+midrange+tweet, based on the distance between your ears - a crossover point of 800hz or so is the 1\4 wavelength of that distance. the reason the midbass placement works (according to the opsodis whitepaper) is that the phase information from the left or right reaches one ear at a time or something to that effect.

i didnt know we were talking about horns for the high frequencies all the sudden : - if thats what you were refering to

opsodis specifically refers to using a conventional 3 way system.


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## thehatedguy (May 4, 2007)

Si senor. horns and mids over there.


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## Regus (Feb 1, 2011)

cajunner said:


> perfect for 3D printing with 'scavenged cavity' or whatever they call it, that you go thin shell and fill in with milkshake.
> 
> if you have a place in the door that works out for the dimensional attributes for the tuned compression chamber, and you've got at least 60" of length, I mean you're not trying to get it down into 40 hz territory, somewhere between 150 and 225 hz should be possible?
> 
> ...


I want to hear more about using the Uni-Q drivers without the tweeters - they come up on eBay quite often and I've occasionally wondered whether you could use them for some novel application this way. As I recall, the tweeter is bolted on from the back of the driver - what would be the rationale for using the Uni-Q with a cavity where the tweeter should be over a conventional driver?


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## thehatedguy (May 4, 2007)

I think he was talking about using the backwave of the driver for bass reinforcement and the front side as a traditional mid/tweeter in the opsodis setup.


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## Regus (Feb 1, 2011)

Gotcha - I thought he meant literally minus the tweeter part (i.e. A tweeterless Uni-Q) as opposed to Opsodis without the closely aligned tweeters (I got the rest). On that subject, I'm still interested in whether you can get the tweeter part to work in the highly reflective environment of a car, as Patrick discussed in the one tweeter thread. It would seem that for the majority of people it hasn't worked out that well so I think probably not, which is a shame as it would solve the problem of unequal path length from sail panel or A pillar mounting.


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## MetricMuscle (Sep 16, 2013)

Regus said:


> I want to hear more about using the Uni-Q drivers without the tweeters - they come up on eBay quite often and I've occasionally wondered whether you could use them for some novel application this way. As I recall, the tweeter is bolted on from the back of the driver - what would be the rationale for using the Uni-Q with a cavity where the tweeter should be over a conventional driver?


The Uni-Q does have a tweeter, it is basically a more perfected coaxial speaker. In the world of Home HiFi, the idea of separating the mid and tweeter is very taboo. As the crossover frequency gets higher, the closer the two drivers crossing over must be, to the point of needing to be coincident or coaxial. A 300Hz crossover point between mid-bass and mid allows many inches of separation.

There are varying degrees of Uni-Q from KEF. From the home stuff any mortal can buy to one of their current creations, Blade. 










Search for Kef Uni-Q and you can get a better explanation once you filter thru all of the sales drama.


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## MetricMuscle (Sep 16, 2013)

Regus said:


> Gotcha - I thought he meant literally minus the tweeter part (i.e. A tweeterless Uni-Q) as opposed to Opsodis without the closely aligned tweeters (I got the rest). On that subject, I'm still interested in whether you can get the tweeter part to work in the highly reflective environment of a car, as Patrick discussed in the one tweeter thread. It would seem that for the majority of people it hasn't worked out that well so I think probably not, which is a shame as it would solve the problem of unequal path length from sail panel or A pillar mounting.


Ooops, never mind, I didn't get what you were actually asking about. 

Didn't *req* suggest that the OpSoDis arrangement for the mid and tweeter wasn't as amazing as it was for the mid-bass, even in his living room with more optimal spacing? I've kinda dismissed the idea of attempting to mount a mid and tweeter this way in my car for a number of reasons, just gonna use it for the mid-bass.


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## Patrick Bateman (Sep 11, 2006)

I've listened to the $30,000 Blade and the $1500 LS50 back-to-back.









*To my ears, the LS50 is just as good as the Blade above 100hz.*

I think it's a great illustration of the law of diminishing returns. If you look at some of the megabuck flagship speakers from Focal and Dynaudio and Kef, you're basically paying for some expensive subwoofers in a big expensive cabinet.









IE, you could probably recreate the sound of the Kef Blade with a $1500 set of LS50s and eight subwoofers. In fact, the Blade cabinet is basically four subs arrayed around a Kef coax!

As long as the subs are within 1-1.5 meters of the LS50, it's basically going to sound like a single speaker. (Because 80hz is over four meters long.)

The trick is to use a LOT of subs, to smooth out the response and get that chest-pounding displacement that the $60,000 Blade has.


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## Regus (Feb 1, 2011)

MetricMuscle said:


> Ooops, never mind, I didn't get what you were actually asking about.
> 
> Didn't *req* suggest that the OpSoDis arrangement for the mid and tweeter wasn't as amazing as it was for the mid-bass, even in his living room with more optimal spacing? I've kinda dismissed the idea of attempting to mount a mid and tweeter this way in my car for a number of reasons, just gonna use it for the mid-bass.


No worries! I was slow on the uptake to start with so really it's down to me - in any case I liked the image of the Blade so no harm done.

Yeah, I think probably midbass is the only thing which would benefit from the OPSODIS approach in a car, although I'm still curious as to why the tweeter arrangement doesn't seem to work out for people, be it in car or out. Perhaps it is just one of those cases where the theory is fine but in practice it doesn't deliver, either because the implementation is technically challenging, the theory itself is incomplete or (as Patrick suggested) it only works well for a small subset of recordings. It could be that you would require a particular approach to recording/mastering/engineering to really deliver the goods, much as in the early days of surround sound the effects were (in my experience at least) somewhat hit and miss, at least until the concept was fully understood and implemented.


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## MetricMuscle (Sep 16, 2013)

Patrick Bateman said:


> I've listened to the $30,000 Blade and the $1500 LS50 back-to-back........
> *To my ears, the LS50 is just as good as the Blade above 100hz.*
> 
> I think it's a great illustration of the law of diminishing returns. If you look at some of the megabuck flagship speakers from Focal and Dynaudio and Kef, you're basically paying for some expensive subwoofers in a big expensive cabinet.
> ...


No doubt the mega amazing mega bux home speakers are as much about the visual impact as the sound but look at the intended market. It certainly isn't the DIYaudio aficionado who knows what good sound is and how to go about making it.



Regus said:


> No worries! I was slow on the uptake to start with so really it's down to me - in any case I liked the image of the Blade so no harm done.
> 
> Yeah, I think probably midbass is the only thing which would benefit from the OPSODIS approach in a car, although I'm still curious as to why the tweeter arrangement doesn't seem to work out for people, be it in car or out. Perhaps it is just one of those cases where the theory is fine but in practice it doesn't deliver, either because the implementation is technically challenging, the theory itself is incomplete or (as Patrick suggested) it only works well for a small subset of recordings. It could be that you would require a particular approach to recording/mastering/engineering to really deliver the goods, much as in the early days of surround sound the effects were (in my experience at least) somewhat hit and miss, at least until the concept was fully understood and implemented.


Maybe *req* didn't have the tweeters and mids far enough away from his listening position. The image in post #57 positions them lots further away. The mid-bass is also further away than what he did but not as much.










Maybe put this on his list to try next time he sets it up assuming he has room.

This would be even more impossible in a car so we may as well not even consider it unless the shorter distance could be compensated for with TA.


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## Patrick Bateman (Sep 11, 2006)

The distance is irrelevant.
The angles *are* relevant.

Basically it goes like this:

1) Draw a circle around the listener
2) Position the midrange, tweeters, and midbasses at specific points on the circle
3) The angle of those points will be dictated by crossover frequency

Taken to the extreme, you could probably do an Opsodis setup with speakers that are less than a meter from your head.










If you really wanted to blow some minds, do this:

1) Get a pile of drivers, kind of like the CBT pictured above
2) Instead of a convex ring make it a concave ring. (IE, it wraps around the listener.)
3) Get four of those $25 digital amps from Parts Express
4) Get two MiniDSPs
5) And then do a four way Opsodis set up. So it would look something like midbass > midrange > tweeter > super tweeter

If you really wanted to go buck wild, you could do a full ring  Just double the drivers and the amp channels. Opsodis already has a plugin for doing surround sound with four channels, in fact the author of the Ambiophonics web site uses four channels of audio.

It's fun all the crazy sh t you can do with cheap DSP and amp boards nowadays 

The best imaging I've ever heard in my life was with a bunch of cheap Logitech speakers. It was at CES, they'd set up a ring of speakers above the listeners. They were using a PC as a source, and a game, and when bullets and explosions happened it sounded completely 3D. You could literally here stuff whizz by your head.


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## cajunner (Apr 13, 2007)

oh what have I done to this fine OpSoDis thread, with talk of back loaded horn implementations taking over the volleys.

minus the tweeter part, is taking away that ambiophonics close angle binary weirdness because it would just get lost in the dash cavity reflections and wouldn't be natural at all, and because if you have high door placement, you've got no obstructions for a coax tweeter to be blocked by, or run into. Anything above the knees, then.

and you reduce reflections, with the door and the stereo stage center pure psychoacoustics at work, with imaging as clear as can be obtained without additional ripples from the center speaker add-on, or adjunct.

I have a thing about phase, I imagine the reason most stock systems are able to maintain an image is from the use of phase control in the form of wide-range single element paper cones. The oval is not just a matter of physical space management, but also pattern control, or directivity and when you introduce width to a direct radiator, it mimics the coverage of a horn mouth, or produces a degree of success like a sweet spot in the 60 degree unilateral of home audio configs.

This phase is unimpeached by crossover, or time delays of the separates variety, center to center is no match for the clarity of a 300 to 3000 hz bandwidth produced from a single point source.

taking this to the logical extreme of putting a 6X9 in the door and using a back loaded horn to create a region of mid bass/midrange output that is exactly between the horn exit and the driver's mounting location, you could say it would be like looking at the stage's corners by looking out of the driver's window for width, and height is achieved by the door location, and pattern control is achieved by rotating that 6X9 until the compromise between near side reflections and creating that large area of coincidence, or imaging where the stage is represented without the rainbow of OpSoDis ever coming into play...

or you could just disregard the thought, either way...


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## req (Aug 4, 2007)

i think the biggest problem with horn loading a midbass that is in-line with your hip area in a car is physically putting it there. even if you can mount it under the seat and squirm the throat\mouth up the B pillar it would still be extremely dificult - and most likely a 1-off thing that is not very easy to modifiy and perfect.

personally, putting a solid midbass in a rear-door that is deadened properly and crossed around 300hz is a very simple way to achieve the added width. 

what i am doing with my bro's ride:

tweets in the sails. 5000ish Hz and up
midrange in the front OEM door location in a 3D printed ported pod (hopefully) - 300 to 5000 hz or so
midbass in the rear doors - 50 to 300 hz or so

im hoping that using conventional tweeter placement and then as on-axis as i can get midrange in the OEM door location - keeping the speakers as wide as possible - will get the image nice and stable.


*as far as the tweeters\midrange oriented in opsodis-like arrangements (we didnt measure the angles and such) the stage\imaging did NOT work.* when i listened to the IASCA CD, the vocals that were center were AWESOME and tight. but as soon as there was supposed to be something, like the pink panther track, the triangle should be far right. but the triangle was located to the front where the tweeters were positioned. as soon as we moved the tweeters wide, the triangle moved with them and it sounded like it had width in the upper frequencies. after doing this, i felt the center was never as good. i assume that i could have gotten the center tighter with EQ\CROSSOVER\TA tuning, but i dont think i could have gotten width without physically moving the tweeters.

if that makes sense


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## thehatedguy (May 4, 2007)

I posted a link to a DB Keele patent for an array for vehicles a while back...

http://www.audioartistry.com/2-12 patents/KeelePatentVehicleLoudspeakerArray.pdf


Anyways, this would be the hot ticket for someone who was rebuilding a dash for a competition vehicle...knew a fair amount about acoustics, and had some serious processing. 



Patrick Bateman said:


> The distance is irrelevant.
> The angles *are* relevant.
> 
> Basically it goes like this:
> ...


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## MetricMuscle (Sep 16, 2013)

Patrick Bateman said:


> The distance is irrelevant.
> The angles *are* relevant.
> 
> It's fun all the crazy sh t you can do with cheap DSP and amp boards nowadays




The distance and angles affect the spacing. It was mentioned on the 1st or 2nd page, if the tweeters are separated by just 6.2 degrees, they won't be very far apart in a car due to not being as far ahead of the listener as in the drawing. If they are lots farther out in front of the listener, they will be farther apart. If we were to figure out how far apart they need to be minimum and place them there, the angle between them will be greater the closer they are to the listener. I suppose TA would only be necessary if they were at a much different distance than the mid.

Where can I educate myself on miniDSP? 
What brands and vendors do you recommend?


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## Hanatsu (Nov 9, 2010)

MetricMuscle said:


> Where can I educate myself on miniDSP?
> What brands and vendors do you recommend?


Buy directly from their site: Welcome to the world of miniDSP | MiniDSP

It can do FIR and allpass filters aside of the "normal" DSP stuff.


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## linkbeat (Dec 20, 2013)

I visited a VW dealer today to satisfy my curiosity. I looked at both the 2013 and 2014 Jetta (and Passat) and neither of them had this setup referenced in the OP. I then found a used 2008 Jetta and it did have that door setup.

The results were interesting though. The 2008 didn't have near the quality that the 2014 had as far as a sound stage goes. The Fender setup on the 2014 with mids in the usual door locations (towards the front) and the tweeters in the pillars produced a really nice sound stage with centered vocals and instruments dispersed across the dash. The 2008 Jetta sounded very driver side biased with a narrow sound stage, I was not impressed at all. When I switched to the passenger seat in the 2014 the sound stage condensed to the far right. It wasn't good from the passenger seat at all. 

Although the fender components were probably better than whatever the 2008 had, I was expecting speaker location to produce something unique. 

Just my thoughts.


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## MetricMuscle (Sep 16, 2013)

linkbeat said:


> I visited a VW dealer today to satisfy my curiosity. I looked at both the 2013 and 2014 Jetta (and Passat) and neither of them had this setup referenced in the OP. I then found a used 2008 Jetta and it did have that door setup.
> 
> The results were interesting though. The 2008 didn't have near the quality that the 2014 had as far as a sound stage goes. The Fender setup on the 2014 with mids in the usual door locations (towards the front) and the tweeters in the pillars produced a really nice sound stage with centered vocals and instruments dispersed across the dash. The 2008 Jetta sounded very driver side biased with a narrow sound stage, I was not impressed at all. When I switched to the passenger seat in the 2014 the sound stage condensed to the far right. It wasn't good from the passenger seat at all.
> 
> ...


*You are lying!* 

You are just trying to distract us from the path to true high fidelity, it's not gonna work!

Ok, forget it, I'm just gonna install some Sony 4-way coaxials and be done with it, I hope you are happy.  

That is interesting. The car is 6 years old so who knows what acoustical abuse it has suffered.



req said:


> .....personally, putting a solid midbass in a rear-door that is deadened properly and crossed around 300hz is a very simple way to achieve the added width.


I have OE vented enclosures in both front and rear doors, both with a full range 5.25" driver. The front door location is about where my knee is. The rear door location is about the same height and on the front of the door so both are close to the same distance from my left ear and also the same distance away from being at exactly the 9 o'clock position.
If I were to locate a new mid higher up on the door and use dedicated mid-bass drivers in all 4 door locations, I think it would still work and maybe even average out the location more to the 9 o'clock position. This would also give me lots more cone area, about that of a pair of 9", and I wouldn't have to cut my door panel, which happen to be in really pristine shape.



req said:


> -midrange in the front OEM door location in a *3D printed* ported pod


Do you have access to one of these printers?
What material would the pod be made of?

We had some experimental parts made at work this way to verify fitment etc. They were a brown resin material, probably strong enough for a small speaker pod. We actually installed the parts and ran the machine and the resin held up. It's not in an overly stressed position but the production parts are made of Stainless. 
Would you do anything to the 3D pod or use as is?


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## MetricMuscle (Sep 16, 2013)

Hanatsu said:


> Buy directly from their site: Welcome to the world of miniDSP | MiniDSP
> 
> It can do FIR and allpass filters aside of the "normal" DSP stuff.


What are the benefits of using these over a DSP like MS-8, PS8 or 360.3 ?


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## Hanatsu (Nov 9, 2010)

MiniDSP is cheaper ;P

Sent from my Samsung Galaxy 3 via Tapatalk.


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## MetricMuscle (Sep 16, 2013)

Maybe some of the smaller ones but the multi channel out is close if not more.


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## Hanatsu (Nov 9, 2010)

Oh, I referring to the 2x4 board. The MiniDSP got some extra features. You can hook it up directly to RoomEQ and transfer autoEQ values simulated directly inside the program to the DSP.


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## ErinH (Feb 14, 2007)

req said:


> *as far as the tweeters\midrange oriented in opsodis-like arrangements (we didnt measure the angles and such) the stage\imaging did NOT work.* when i listened to the IASCA CD, the vocals that were center were AWESOME and tight. but as soon as there was supposed to be something, like the pink panther track, the triangle should be far right. but the triangle was located to the front where the tweeters were positioned. as soon as we moved the tweeters wide, the triangle moved with them and it sounded like it had width in the upper frequencies. after doing this, i felt the center was never as good. i assume that i could have gotten the center tighter with EQ\CROSSOVER\TA tuning, but i dont think i could have gotten width without physically moving the tweeters.
> 
> if that makes sense


I know exactly what you're talking about. I played around with using a tweeter in the physical center of my two mids (mounted in the pillars) and while the focus was obviously much tighter, the image was never as developed when wide. In some ways, it essentially does the opposite of what most people have an issue with; it 'walked' things toward the center. I tried summing to mono (not a good idea) and I also did plain stereo with the tweeters put in the middle. I gave up and went with the norm. Then, I tried it again a few months later when messing with ambio and still had the same result. Ultimately, it just wasn't something I saw a benefit from.

Speaking of ambio, heck, I even tried ambio for each seat (using multiple aura ns3's, each pair in front of each listener). The methods, while intriguing, simply don't pan out... or they didn't for me. Neither at home or in the car. The ambio manipulates the music to a degree that it's sometimes annoying. While it sounds really cool on some tracks, it sounds horrible on others. 



thehatedguy said:


> I posted a link to a DB Keele patent for an array for vehicles a while back...
> 
> http://www.audioartistry.com/2-12 patents/KeelePatentVehicleLoudspeakerArray.pdf
> 
> ...


I actually drew my inspiration from his white papers/briefings and attempted to implement it in my car last year. The problem was to get it to work to any realistic degree, the install was assymetric in the car. The to-the-side, nearfield sitting really does a number on the CBT theory, when the 'speaker' is toppled like that. Taking a speaker like what was posted and 'putting' that in a car (for a lack of better words) didn't work out for me the way I had hoped. I took the idea, knowing that the car itself curves and that I'd have to apply some shading via DSP (ie; steered phase array) soooooo... I had 2 DSPs and about 12 channels of processing for (4) pairs of 'speakers', where each 'speaker' consisted of (2) NS3's + (1) CSS LD25X. Each set of mids was in series, and the tweeter was on it's own, making each 'speaker' an active 2-way. (that's all a mouthful; hopefully it makes sense)

After about a week of playing around with speakers on my dash, I punted. I *might* have been able to pull off uber sound, but not without using more amplifiers and DSP channels than I could afford or building passives that I didn't want to build. That said, what really stopped me was the fact that my civic dash isn't as wide open as I had hoped. They practically stuff Wal-Mart inside that thing, man. 

I really, really, wanted it to work, namely because it's so ... different, at least relative to car audio, but I felt I was better off with the KISS method. 

Now and again, I get the urge to try this stuff out again. I started with Gerzon's white papers on listening and recording and ultimately found my self trying a make-shift phased array (as mentioned above), but there were just too many complications for me. IF I had Steve Cook skills, I'd rip the dash out and get to work. Or, I'd let Eldridge build it for me if I had the cash. 

I definitely think there's merit in the idea of applying CBT type theory to the car... I just know that practicality is low; and frankly, unless you have a lot of space to work with, you will still have to compromise the passenger seat to fine tune the driver seat. Still, had it not been for my efforts and research in to Keele's work, I wouldn't have really grasped on to the importance of polar response, which ultimately is what led me to the kef's I'm using in the car.


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## ErinH (Feb 14, 2007)

speaking of the kef LS50, I've yet to hear those but would really like to. I ordered up the Q100 to test last year and was so impressed with it, I doubled-down and bought the R500's for my HT. Then a set of the R500 concentrics went in to my car. 

I'd never heard a set of speakers image like that. It's just unreal.


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## thehatedguy (May 4, 2007)

I was going to buy the 8s from Speaker Exchange, and you can't get them over the counter now...have to have a serial number.


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## linkbeat (Dec 20, 2013)

MetricMuscle said:


> *You are lying!*
> 
> You are just trying to distract us from the path to true high fidelity, it's not gonna work!
> 
> ...


You know this parade you have going here? Imma rain on it!!!

Yeah who knows, all kinds of variables involved. I do have to say that it would have to be pretty magical to get equal path length sound out of a setup that is very unequal.


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## ErinH (Feb 14, 2007)

thehatedguy said:


> I was going to buy the 8s from Speaker Exchange, and you can't get them over the counter now...have to have a serial number.


those 8's have a pretty nasty breakup. a good notch filter (or narrow Q EQ) would help that, though.


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## req (Aug 4, 2007)

bikinpunk said:


> I know exactly what you're talking about. I played around with using a tweeter in the physical center of my two mids (mounted in the pillars) and while the focus was obviously much tighter, the image was never as developed when wide. In some ways, it essentially does the opposite of what most people have an issue with; it 'walked' things toward the center. I tried summing to mono (not a good idea) and I also did plain stereo with the tweeters put in the middle. I gave up and went with the norm. Then, I tried it again a few months later when messing with ambio and still had the same result. Ultimately, it just wasn't something I saw a benefit from.


exactly my findings


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## MetricMuscle (Sep 16, 2013)

Wow, it's been a month since we chatted about this.

Has anybody experimented with this concept at all, especially in the mid-bass department?


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## req (Aug 4, 2007)

at least anyone but me? 



maybe ill bring my _*"5 gallon ANARCHY buckets"*_ to the north carolina meet and see if we can put them into the demo rig and bypass the mids on the towers or something.

that would be interesting.


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## Hanatsu (Nov 9, 2010)

I will try the opsodis midbass placement in my current build. The modal suckout at 180Hz moved 25Hz upwards when I moved the test enclosure to the back of the door, much better in my setup. If it stages better, it's a bonus 

I'll be sure to post my findings, might take a month before I get there though...


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## thehatedguy (May 4, 2007)

I would be curious about the whole thing too.


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## Orion525iT (Mar 6, 2011)

I am really curious about this too. However, I don't think I will be moving my 8" midbass out the kicks in my BMW. I got my hands full with everything else in this build, and I put a ton of work into the kicks.

On a side note, I will be getting a used little two door in the spring. I have already been eying pictures of the side panels that flank the rear seat. They look to be the perfect size for the 8" type Rs I tried in the BMW before switching to the Daytons. SInce I am tall, I usually sit far enough back that my ears are in line with the front of the rear door as opposed to the rear of the front door. So the opsodis is a logical route in that car once I get it.

In the BMW, I did test an opsodis-like arrangement. But it is a bit different than what everyone is focusing on here (midbass placement). I have the midbass in the kicks with fullrangers just in board of thr midbass. Staging was goood with good L/R separation. But the it sounded thin and was very sensitive to head position, which is not surprising with the fullrange drivers. I then tried center mounted tweeters without caping the fullrangers. The results were pretty interesting. I still had good L/R separation, but head position was less critical and top end sounded fuller. I really like the way it sounded, although it may not be exactly competition worthy. I hope to experiment with this more once I get decent processing.


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## req (Aug 4, 2007)

hanatsu - cant wait for all your cool graphs and such to display your thoughts on the arrangement.


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## roduk (Sep 19, 2008)

Hanatsu, any progress? I have a mkv golf with the exact setup that Patrick raves about in the first post and am just about to embark on an sq project in it...

My logic says put the speakers as far in front of me to produce a decent soundstage, but if the midbass are going to work firing into my bum then what do I know??!!

Would love to know more if anyone has been playing?!


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## damonryoung (Mar 23, 2012)

roduk said:


> Hanatsu, any progress? I have a mkv golf with the exact setup that Patrick raves about in the first post and am just about to embark on an sq project in it...
> 
> My logic says put the speakers as far in front of me to produce a decent soundstage, but if the midbass are going to work firing into my bum then what do I know??!!
> 
> Would love to know more if anyone has been playing?!



I use my factory locations with this exact setup and had someone help me with the tune. He was a little shocked that the midbass play up on the dash without problem.... 

I would say if you use this setup, to make sure you deaden the doors thoroughly. I removed the outer door skins to make sure this was done...


Beware of autocorrect...


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## Orion525iT (Mar 6, 2011)

roduk said:


> Hanatsu, any progress? I have a mkv golf with the exact setup that Patrick raves about in the first post and am just about to embark on an sq project in it...
> 
> My logic says put the speakers as far in front of me to produce a decent soundstage, but if the midbass are going to work firing into my bum then what do I know??!!
> 
> Would love to know more if anyone has been playing?!


A few guys working on similar arrangements.

http://www.diymobileaudio.com/forum...odus-helix-pdsp-idmax-carpc-*updated*-36.html

I plan to implement a variation in a coupe, which will differ in some areas, but operate off the same science. The project won't take off 'till mid summer though.

Why you waiting on someone else? Break ground yourself! You may fail, but you learn from the process. There is not a magical formula. If there was, we wouldn't need this site.


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## Patrick Bateman (Sep 11, 2006)

Patrick Bateman said:


> The distance is irrelevant.
> The angles *are* relevant.
> 
> Basically it goes like this:
> ...


Jason had mentioned that this would be a great setup for a car

One problem with this setup is that it's curve; IE it's a lot easier to put a straight array in a car than a curved array

It's interesting to find that the owner of this array has opted to go for a straight array, and is doing the 'curvature' via DSP delay now


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## thehatedguy (May 4, 2007)

I think the array has or is being used in 2 competition cars...well 1 that has been winning everything for a long time and another rebuild of a Legend (the car is a legend in SQ and is also a Acura Legend) that hasn't made it into the lanes yet. Same guy out in the flat lands built both of them.


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## ErinH (Feb 14, 2007)

Yep. You're right. 

I'd love to go that way myself... Just no space in my little civic.


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## thehatedguy (May 4, 2007)

Did the VW in the original post have the Fender system in it? A good friend of mine and old Image Dynamics teammate Natan Budiono is with them now. Natan has been in the OEM car audio business for a long long time.


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## Patrick Bateman (Sep 11, 2006)

thehatedguy said:


> Did the VW in the original post have the Fender system in it? A good friend of mine and old Image Dynamics teammate Natan Budiono is with them now. Natan has been in the OEM car audio business for a long long time.


Yes I believe it was the Fender system


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## thehatedguy (May 4, 2007)

Natan also did a lot of work on the Acura TL system that everyone liked. 

Super cool guy...always said my car sounded a lot like his.


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## sensarmy (May 25, 2014)

Patrick Bateman said:


>


mother of god


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## thehatedguy (May 4, 2007)

If anyone outside of the MECA circle in the south and midwest, Ben Vollmer (who is a good friend to many of us and owns Audition Audio and Electronics) bought what was once Harry Kimura's Acura Legend and after it spending many years in limbo around Tennessee with it's previous owner, Georgia and here in North Carolina, and it made it's way to Mobile Soundstage Engineering in Bixby, OK where it underwent a COMPLETE rebuild by Mark Eldridge...including an array front stage.


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## jnchantler (Apr 11, 2012)

Patrick Bateman said:


> Yes I believe it was the Fender system


I'm 99% sure that's not the fender system. I used to have the same car. The Fender systems had a logo on the sail panels which I don't see in that car.


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## Patrick Bateman (Sep 11, 2006)

thehatedguy said:


> If anyone outside of the MECA circle in the south and midwest, Ben Vollmer (who is a good friend to many of us and owns Audition Audio and Electronics) bought what was once Harry Kimura's Acura Legend and after it spending many years in limbo around Tennessee with it's previous owner, Georgia and here in North Carolina, and it made it's way to Mobile Soundstage Engineering in Bixby, OK where it underwent a COMPLETE rebuild by Mark Eldridge...including an array front stage.


That's the second 'horn dude' I know of that switched over to the dark side. (IE, "line arrays")

The first was D.B. Keele


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## req (Aug 4, 2007)

well.

so far, there are certain bandpass that play up on the dash that really make you try to hear it coming from behind, and there are certain areas that pull back around my shoulders or the headrests. i have not done any EQ, and only have basic time alignment and levels set. ive been driving around for about two weeks with it so far.

theres times where i am like 'holy crap this is awesome' and times where im like 'i wonder what frequencies this is becuase its pulling back a little'. most of the time, the tight punch of a kick-drum will be way up front, maybe because the incident sound is from the midrange, followed by the midbass? and most of the time i end up hearing rolling bass guitar pulling backward toward the "rear" midbass.

i have not had much time to expierment.


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## thehatedguy (May 4, 2007)

A lot of work for some little speakers back there.


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## Orion525iT (Mar 6, 2011)

Req,

What frequency do you have them crossed?

My sub manifolds are going in the same spot, but will only play up to 150hz, where the mids will take over. The experiments I have done in my living room, the manifold does not pull my ear back as long as I have mids taking over from 150hz, and tbose mids are placed to the left and right Opsodis style.


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## sqnut (Dec 24, 2009)

I have a question. 

Vertical arrays have better horizontal dispersion and vice versa.










Every time you sit in the car your ears position will vary more on the x axis while on the y axis they will more or less be at the same height. Hence you are looking for an array that gives better lateral dispersion, i.e. vertical arrays.

the same should apply while mounting a mid and tweet on dash/pillars. Tweeters above the mid (vertical array) should work better than tweeters besides the mid (horizontal array). Is this reasoning correct?


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## req (Aug 4, 2007)

i could have put a larger speaker, like an 8 or a 10 in there, but the opening+grill for the OEM speaker is still less than 6.5 inches. plus i didnt feel like buying new hardware to test and see if this even worked. i didnt buy anything besides a few bolts for this expierement - i had some wood laying around and i just re-located the midbass speakers. plus, technically, i could fit into a lower competition class due to using the OEM speaker locations and sizes haha (if i didnt have the carPC) but im not bothering with competition anymore - so i guess its a moot point.

orion - iv been playing with the slope and xover point between 150~300hz, and it seems that a steeper slope closer to 150hz mitigates it more just as you have said (i just lowered it yesterday actually). i have to do some more playing around with it and re-listening to the same material though... as well as make sure i dont push too much bass to my midranges. 

ill see what i can do about lowering it to 150 and playing with it a bit more, and ill get back to you.

is there a specific track you are listening to that i could use so that we may be on the same page?


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## sqnut (Dec 24, 2009)

req said:


> orion - iv been playing with the slope and xover point between 150~300hz, and it seems that a steeper slope closer to 150hz mitigates it more just as you have said (i just lowered it yesterday actually). i have to do some more playing around with it and re-listening to the same material though... as well as make sure i dont push too much bass to my midranges.
> 
> ill see what i can do about lowering it to 150 and playing with it a bit more, and ill get back to you.


You can start locating front/back around 70hz. If you're using the rears as subs I'd keep them ~60hz and under on 6th order slopes. If it still pulls to the rear play with TA between the rear and front mid bass. Low end on bass guitar is 80-125hz.


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## Patrick Bateman (Sep 11, 2006)

req said:


> well.
> 
> so far, there are certain bandpass that play up on the dash that really make you try to hear it coming from behind, and there are certain areas that pull back around my shoulders or the headrests. i have not done any EQ, and only have basic time alignment and levels set. ive been driving around for about two weeks with it so far.
> 
> ...











Use this picture as your guide. It was setup by the Opsodis folks, and I have a heck of a time reading their papers, likely because Japanese is their native tongue.

Our perception of frequencies below 500hz is determined by phase. Due to this, we have a few options. The first option is to put the speakers hard to the left and hard to the right, like the Opsodis folks did above. *Note that it's not sufficient to get the angle right; you have to get the distance right too.* But here's the important thing; if you CAN'T get the distance right, you can 'fake' the distance using DSP delay. IE, you CAN'T fake the angle, but you CAN fake the distance.



TLDR : With the midbasses located to the left and to the right you'll need some delay for the left channel. Without delay, your center is going to shift to the left. You'll also want to cut the level of the left midbass by a few decibels, to compensate for how close it is to you.


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## Patrick Bateman (Sep 11, 2006)

On second thought, you *could* fake the angle of the midbass using crosstalk cancellation. But doing that really nukes your dynamics, and the only way it's 100% effective is if you're able to nuke the crosstalk 100%... which is physically impossible.

I am using crosstalk cancellation in my home setup, and it works nice in the midrange but I don't find it to be worth the trouble below 250hz or so. I use it from 250hz (54") to 2khz (6.75") Basically I use it in the frequencies where the wavelengths are too long for waveguides, but not so long that the crosstalk cancellation is totally ineffective. To me it seems like you get the most 'bang for the buck' in the two octaves from 500hz to 2khz.


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## Patrick Bateman (Sep 11, 2006)

req said:


> is there a specific track you are listening to that i could use so that we may be on the same page?


One really easy way to determine width is to record some pink noise at various locations in the stage. Basically here's how you'd do it:

1) get a wav of pink noise (google it)
2) load that wav into Audacity
3) and then pan from the left to the right. Something like ten steps would be optimum
4) Once you have your ten wav files, record them on a CD

If you really wanted to go nuts, you could do this for every octave too. Basically chop up the pink noise into ten octaves, and repeat steps 1-3.


The ambiophonic VST plugin has a tool built in that does this. It's really a trip, because you can *immediately* tell if your stage is set up right. For instance, in my setup, I can tell that the left channel is better than the right... When it pans to the right there's a 'hole' next to me. This 'hole' is due to geometry. Basically I'd have to fiddle with DSP and EQ to fill in that hole.


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## Orion525iT (Mar 6, 2011)

req said:


> i could have put a larger speaker, like an 8 or a 10 in there, but the opening+grill for the OEM speaker is still less than 6.5 inches. plus i didnt feel like buying new hardware to test and see if this even worked. i didnt buy anything besides a few bolts for this expierement - i had some wood laying around and i just re-located the midbass speakers. plus, technically, i could fit into a lower competition class due to using the OEM speaker locations and sizes haha (if i didnt have the carPC) but im not bothering with competition anymore - so i guess its a moot point.
> 
> orion - iv been playing with the slope and xover point between 150~300hz, and it seems that a steeper slope closer to 150hz mitigates it more just as you have said (i just lowered it yesterday actually). i have to do some more playing around with it and re-listening to the same material though... as well as make sure i dont push too much bass to my midranges.
> 
> ...


In regards to music and tracks, nothing real specific. For tracks I listened to Radiohead -_Weird Fishes_ and Rusted Root - _Cruel Sun_. For entire albums it was more EDM/electronic/ambient type stuff. Aioaska - Into the Cosmic Jungle and Sysyphe - Under the Wood. Might be some better reference tracks than what I used.

As far as my whole system design, it's a bit different. The subs are eight 8" manifold PPSLs and will be mounted in the quarters. They vent back over the shock tower and exit into the trunk. I was planning on sealing the trunk, but my experiments with manifold OB has taught me that sealing the trunk may not be needed or wanted. Those subs will play to 140hz. 

I have four PM180-8 for midbass. They have very good sensitivity, but don't play too low. But, because of the subs, they don't need to do so. One pair will go in .16 cu ft sealed pods (F3 150hz) in the doors at the hard left and hard right positions. The other pair will go in .16 cu ft pods at essentially the location of the stock system at the front of the door. There are many reasons why I decided on this arrangement, but I was trying to get some benefit of Opsodis and the theoretical benefit of midbass arrays. I was worried about localization cues from midbass in the quarters, but I also realized that placing large midbasses at the back of the door in the hard left and hard right positions would be a very bad idea on multiple fronts. 

Crossover points: So this is were things get a bit different. The subs are in the quarters, stereo crossed at 140hz. The midbass to the hard left and hard right pick up from 150hz and play to 600hz. Now the front midbass, play from 150hz all the way out to 2200hz. The upper end has not been determined. I may use just a tweeter, or I may use some small midrange, and then super tweeter inboard of that or even centered on the dash. 

Sounds like a mess, no?

So I did a test in the house, which differs slightly from what I plan to do in the car. I had one pair of PM180-8 in front playing from 150-2200hz crossed to tweeters. I placed the other pair of PM180-8 to my hard left and hard right. I placed one of the sub manifolds directly behind me. 8 channels of processing. I played the front stage (PM180-8 + tweeter) with the subs crossed at 150hz. It sounded good, but at 150hz I could detect some rearward pull with some bass notes. Stage was just outside of the speaker width.

I then turned on the channels to the PM180-8 at the hard left and hard right. These midbasses were time aligned to play just ahead of the rest of the drivers. I immediately noticed a much wider stage, a la Opsodis.

Can anybody guess what else happened?


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## Patrick Bateman (Sep 11, 2006)

In my experience this type of a setup sounds more 'spacious', but a lot will depend on the directivity of your drivers and how 'live' your room is.


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## Orion525iT (Mar 6, 2011)

Patrick Bateman said:


> In my experience this type of a setup sounds more 'spacious', but a lot will depend on the directivity of your drivers and how 'live' your room is.


Some other observations:

1) Yes definitely more "spacious". A bit more "enveloping" but not at all headphone like 

2) I could not hear the position of the midbasses to my sides at all. Even though I immediately heard a huge difference in the stage when the channels were flipped on and off, I literally had to reach down and feel the cones to make sure they were moving. They were played at the exact same levels as the front midbass.

3) In reaching down to the cones and turning my head in the process, I noticed that head turning was not an issue. I could turn my chin from my left shoulder to my right shoulder, and the image stayed in front without localization.

4) Not only could I not localize the side midbass drivers with them on, the front drivers became much more transparent also. 

5) Here is the neat bit that I alluded to; The bass cues I was getting from the sub manifold mounted behind me disappeared. I turned the side midbass drivers on and off several times on several tracks just to be sure, and everytime the rearward bass cues disappeared. I think the side midbass were pulling the cues forward in way that the front midbass could not. The big question is, why?


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## Patrick Bateman (Sep 11, 2006)

Think about it this way:

1) Let's say you're in a room with one person talking. It will be easy to tell where they are.
2) Now do the same thing in a room with ten people. *You can still pick out the location of the person, but the additional cues will make it more difficult.*
3) Now try and listen to someone who's ten feet away from you, while someone else who's five feet away is talking to you. The cues from the nearer person are going to obscure the cues coming from the farther person.

I'm kinda curious to try varying the height to see if multiple midbasses can make the stage higher. IE, you don't want multiple tweeters because they're going to interfere with each other. But midbass frequencies are so long, you have a lot more freedom to vary their location. (As you found.)




It's complex though. The other day I went to a restaurant in Del Mar that was fifty feet from the ocean. Seated outside, I found that it was nearly impossible to hear people, even people five feet from me. My hypothesis is that the sound of surf crashing is so loud, and the sound so random, that it was drowning out conversations happening just five feet from me. It was truly distracting; some of the worst acoustics imaginable.


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## Orion525iT (Mar 6, 2011)

^ All of this .

Its not that the side midbasses are so loud that they are drowning out the other cues (as stated before, I can't actually hear the side midbass playing) it is more of an arrival thing and saturation. I did state that I TA'ed the side midbass to arrive just a tiny bit ahead of everything else. 


Lots to play with here.

FYI, the side midbasses were on the floor to either side of my office chair (not optimum angle, in fact, a sharper angle than will be in the car) and the front midbass were at desk height with the tweeters.


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## damonryoung (Mar 23, 2012)

So, I've got the same factory locations as in the OP and have found them to be very good.

When I had the system tuned the center image ended up being a little bit to the right for me when I placed my head on the head rest. After a discussion with the tuner I found out that his head was a few inches ahead of mine while the seat was in the same position. Now what I have found interesting is that when my head is back the center is solid and focused, but a little to the right. If I move my head closer to where it was tuned, it is still solid and focused now more dead centered. 

Could this have anything to do with the location of the midbass??


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## Patrick Bateman (Sep 11, 2006)

DRTHJTA said:


> So, I've got the same factory locations as in the OP and have found them to be very good.
> 
> When I had the system tuned the center image ended up being a little bit to the right for me when I placed my head on the head rest. After a discussion with the tuner I found out that his head was a few inches ahead of mine while the seat was in the same position. Now what I have found interesting is that when my head is back the center is solid and focused, but a little to the right. If I move my head closer to where it was tuned, it is still solid and focused now more dead centered.
> 
> Could this have anything to do with the location of the midbass??


The answer to that question is really going to depend on the frequencies in question.


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## damonryoung (Mar 23, 2012)

Patrick Bateman said:


> The answer to that question is really going to depend on the frequencies in question.


HP 90Hz w/ 12db 
LP 315Hz w/ 24db


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## Patrick Bateman (Sep 11, 2006)

DRTHJTA said:


> HP 90Hz w/ 12db
> LP 315Hz w/ 24db


No I mean the frequencies you were playing, not the crossover points 

That's why pink noise is so invaluable in testing. You can spend an hour listening to fifteen music tracks, and most of the imaging cues will likely be in the midrange. Pink noise covers all the bands.


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## Regus (Feb 1, 2011)

Orion525iT said:


> ^ All of this .
> 
> Its not that the side midbasses are so loud that they are drowning out the other cues (as stated before, I can't actually hear the side midbass playing) it is more of an arrival thing and saturation. I did state that I TA'ed the side midbass to arrive just a tiny bit ahead of everything else.
> 
> ...


Interesting stuff going on here!

Was the TA of the side midbasses done to simulate closer proximity in a car or was it done for the reason Patrick mentioned about distance being important for an OPSODIS setup to work effectively? Or was it something else entirely?

Also, I assume you didn't try the midbasses without the frequency overlap/with the fronts playing from where the side midbasses stop, or you'd haved mentioned it? Of course, this would defeat the object of having an array of midbass speakers, but I was thinking of doing an OPSODIS style system where the side midbasses alone play down to where the sub(s) take over - looks like I might need to rethink my plans!


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## Orion525iT (Mar 6, 2011)

Regus said:


> Interesting stuff going on here!
> 
> Was the TA of the side midbasses done to simulate closer proximity in a car or was it done for the reason Patrick mentioned about distance being important for an OPSODIS setup to work effectively? Or was it something else entirely?


I don't think he said this, pretty sure it is the opposite. Distance dose not matter, what matters is angle. This has to do with ITD and phase. 

In regard to TA of the midbass. You can't TA the ITD. If you have midbass (as in an array, or typical 3-way) at the front of the doors, your stage width may suffer due to the angle and decreased ITD. This is the theory behind the Opsodis, to move the midbass to a location where the ITD is the greatest. 

Now consider a midbass array. The issue here is phase again. You can TA the speakers to correct for distance anomalies, but it *does not* fix phase differences. You *can* use some L-R processing to correct, as highlighted in the midbass array thread, but that has issues too. Patrick mentioned the loss of dynamics as one of the problems, IIRC. Outside of that, it requires a lot of processing.

So the idea was a hybrid Opsodis/midbass array. My hypothesis is that the concern over phase may not be an issue, because at midbass frequencies we can leverage Haas. You make the Opsodis midbass reach your ear before the array midbass, and your brain doesn't know the difference. There are other little details here that I think are very important, but that is the basic hypothesis. I think Patrick mentioned a 10db threshold on the precedent effect, which is huge.

So I am leveraging Haas and ITD, but I am also leveraging saturation, which is the key idea behind the midbass arrays.

Haas and saturation also come into play with the subs too, which is why I can play the subs directly behind me at 140-150hz without the stage pulling back on bass notes. It is why the bass notes pulled behind me when I turned off the channels to the Opsodis midbass. In the car, the subs will be stereo and flanking, which should improve things even more over the living room set up.

The subs do the heavy lifting, while the midbass frequencies are essentially anchored to the Opsodis midbass. 



Regus said:


> Also, I assume you didn't try the midbasses without the frequency overlap/with the fronts playing from where the side midbasses stop, or you'd haved mentioned it?
> 
> Of course, this would defeat the object of having an array of midbass speakers, but I was thinking of doing an OPSODIS style system where the side midbasses alone play down to where the sub(s) take over


This is because I factored in processing channels and amp channels. I am limited to eight channels right now. Yes, eliminating the overlap would defeat any benefit of arrays. The overlap also gives me more output to match the subs. 



Regus said:


> looks like I might need to rethink my plans!


Why? I would encourage you to experiment. This just one idea, and you must be cognizant of the fact that this was set up in my living room; things may fall apart in actual application. I am also willing to except that there are problems that my ears cannot detect at this point. It takes time to train your brain to pick up on issues you don't notice the first time around. I can already think of 2 dozen or so variables to juggle, each with potential compromises.


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## RocketBoots (Apr 16, 2011)

Orion525iT said:


> I am really curious about this too. However, I don't think I will be moving my 8" midbass out the kicks in my BMW. I got my hands full with everything else in this build, and I put a ton of work into the kicks.
> 
> On a side note, I will be getting a used little two door in the spring. I have already been eying pictures of the side panels that flank the rear seat. They look to be the perfect size for the 8" type Rs I tried in the BMW before switching to the Daytons. SInce I am tall, I usually sit far enough back that my ears are in line with the front of the rear door as opposed to the rear of the front door. So the opsodis is a logical route in that car once I get it.
> 
> In the BMW, I did test an opsodis-like arrangement. But it is a bit different than what everyone is focusing on here (midbass placement). I have the midbass in the kicks with fullrangers just in board of thr midbass. Staging was goood with good L/R separation. But the it sounded thin and was very sensitive to head position, which is not surprising with the fullrange drivers. I then tried center mounted tweeters without caping the fullrangers. The results were pretty interesting. I still had good L/R separation, but head position was less critical and top end sounded fuller. I really like the way it sounded, although it may not be exactly competition worthy. I hope to experiment with this more once I get decent processing.


What year/model bmw do you have? The newer ones have an 8" midbass under the seat. Not quite the Opsodis, but it sort of becomes an omni-directional radiator. Do you think there is any Opsodis going on in this type of setup? Also, where are your full rangers?? Didn't exactly get that. 

Midbass in the back like req did almost seems like it is not Opsodis, since it's sort of like having them in front of you, but since our ears are shaped like a front tilted radar dish it seems to work well. 

I haven't heard anything about how Opsodis affects tonality,timbre, etc. any comments?? To me, those are first priority.

I'm gonna try to implement some of the Opsodis in my next build. Really cool stuff.


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## Orion525iT (Mar 6, 2011)

RocketBoots said:


> What year/model bmw do you have? The newer ones have an 8" midbass under the seat. Not quite the Opsodis, but it sort of becomes an omni-directional radiator. Do you think there is any Opsodis going on in this type of setup? Also, where are your full rangers?? Didn't exactly get that.
> 
> Midbass in the back like req did almost seems like it is not Opsodis, since it's sort of like having them in front of you, but since our ears are shaped like a front tilted radar dish it seems to work well.
> 
> ...


The BMW is an e34, kick area is huge. The widerange drivers were in board of that. No, I do not think the newer BMW are getting any Opsodis benefits, they are using that area because there is space to do so. If you are having a hard time understanding why, there are many blogs, websites and even videos on youtube that can help you visualize how ITD works. 

I can't make any statements about "tonality" or "timbre". The living room experiment was just me trying to validate my hypothesis. Things will be different in the car. My gut feeling right now is that leveraging Haas may have an adverse effect on dynamics. It's going to take a bunch of seat time and tuning to sort it all out.

In regards to req car, he may have better ideas than me, but that arrangement still hold promise I think. The benefit of the quarters is that he can get those midbass pretty wide relative to other placement options (more Opsodis like), but the issue is that he is getting rearward cues because he is playing them fairly high into the midbass.


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## Patrick Bateman (Sep 11, 2006)

RocketBoots said:


> What year/model bmw do you have? The newer ones have an 8" midbass under the seat. Not quite the Opsodis, but it sort of becomes an omni-directional radiator. Do you think there is any Opsodis going on in this type of setup? Also, where are your full rangers?? Didn't exactly get that.
> 
> Midbass in the back like req did almost seems like it is not Opsodis, since it's sort of like having them in front of you, but since our ears are shaped like a front tilted radar dish it seems to work well.
> 
> ...


When we talk about OPSODIS, we have to be careful to qualify it. There's OPSODIS *without* processing, and OPSODIS *with* processing. Both methods work; here's some pros and cons:

1) Opsodis without processing has timbre that's basically equivalent to a 'normal' stereo triangle. *This is because low frequency wavelengths are so long.* For instance, 250hz is over a meter long! So if you move your speaker from the front of the door to the back of the door, like Volkswagen did, the timbre isn't going to change because comb filtering just isn't an issue at 250hz. Now try this at 1khz and it *will* cause issues; 1khz is a third of a meter.

2) Opsodis with DSP delay shouldn't screw up the timbre, in fact it might improve it because you can line up the wavefronts. (IE, if your tweeter is a meter away and your midbass is a quarter of a meter away, inserting a delay for the midbass can sync up the wavefronts, thereby improving timber *and* imaging.)

3) Opsodis with crosstalk cancellation gets tricky. That *will* change the timbre. It is particularly noticeable at low frequency. I <3 my miniAmbio, but the fact that you can't limit the crosstalk cancellation to midrange only is a p.i.t.a. (You CAN limit it with the VST plugins.)

I can barely wrap my brain around the Opsodis papers, they're very hard to follow. But they seem to indicate that the commercial implementations use both crosstalk cancellation (to widen the stage) and EQ (to change your perception of location, by mimicing the pinnae cues of your ear.)

The reviews on the commercial Opsodis speakers are pretty iffy, and I wonder if a big part of that is because the manufacturers have the speakers crammed into such a narrow box. IE, it's fine to put the midrange and the tweeter directly in front of you *but you really need to get that midbass out further.* The midbass location is basically going to dictate the shape of the stage. If it's to your immediate left and right you'll get a soundstage that seems to wrap around you. If you put it in the 'normal' location for a stereo triangle, it will sound like a normal stereo triangle but without the hole in the middle. But if you put the midbass in a Soundbar, like Marantz and Sherwood do, the width of the stage will be the width of the soundbar... Or about 3/4 of a meter. Tiny.


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## Patrick Bateman (Sep 11, 2006)

Some people were wondering if putting the midbass behind you will work. It seems like a strange location. This actually *does* work, because the key is maximizing the interaural time delay. 








*The maximum interaural time delay is achieved when the midbasses are immediately to your left and to your right.* But moving them backwards a bit, to your rear doors, isn't a heck of a lot different than moving them forward. Again, the KEY is the ITD.

Here's a quote from the Robert Hartman paper:

"It is well established that ITDs tend to dominate overall perception, which this research supports."

The Hartman paper is fantastic BTW, much easier to follow than anything from the Opsodis folks : UNIVERSITY OF MIAMI

It was Hartman that got me interested in all of this, because his writing is a lot easier to digest. Choueri (sp?) at Princeton, Glasgall at Ambiophonics, Opsodis, they're all chasing after the same thing. All of their methods are variations on the same thing. Hartman and Ambiophonics aren't selling anything, so they don't bother to obscure any of their tricks.


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## Patrick Bateman (Sep 11, 2006)

Here's a tantalizing idea for those of you daydreaming at work:









The problem with line arrays is that they make *everything* sound big, and the high frequencies sound weird due to the comb filtering. The "big" sound is pleasant, but it is not hifi. It makes a solo voice sound as big as a piano. But it IS fun.









Line arrays with a single tweeter fix the comb filtering problem, but create a new problem. That problem is called "pattern flip." Pattern flip basically means that the directivity changes with frequency. For instance, the woofers have a *narrow* vertical pattern, but the tweeter has a *wide* vertical pattern. Due to this, the tonality around the crossover point is completely wonky. Even if the frequency response is ruler flat, it won't SOUND flat, because of the pattern flip.

Pattern flip really sucks; it's basically unfixable. IMHO, the main reason that so many people struggle to make horns sound good in a car is because of pattern flip. (The pattern of the horns does not match the pattern of the midranges.) Pattern flip is also the reason that people have a hard time integrating planar speakers, particularly big planar speakers. If you've threads where people are struggling with those integration issues, you are reading the frustrations of people battling pattern flip.

























The solution to problem number one and problem number two is an eXpanding array. Dave Smith patented the expanding array when he worked at Snell. Smith has one of the best resumes I've ever seen; he's worked for JBL, McIntosh, Snell, and half a dozen heavyweights that I'm too lazy to Google. He is currently at Bose. Basically the eXpanding array takes the good stuff from option one, the BIG soundstage and the dynamics, but it doesn't have the drawbacks of option two. *It doesn't have pattern flip.*

The reason it doesn't have pattern flip is because each driver hands off to a larger driver as it begins to beam.


OK, everyone with me?


Now here's the FUN part, the daydreaming part. *There's really no reason you couldn't do this with ten drivers, a hundred drivers, heck even a THOUSAND drivers.*









Everyone was jizzing over Dolby Atmos, but you could actually do something similar to Atmos with an eXpanding array.



At this point I've probably lost everyone, and if I had time, I'd make a picture. But here's what I'm suggesting:


1) The Snell eXpanding array has seven drivers per channel. The Dunlavy has nine. You can see where this is going; any number of drivers will work. Just decide how big you want your soundstage to be. The bigger the stage is, the more drivers you'll need. Taken to the extreme, you could probably make a vertical array that had fifteen or even twenty five drivers. In the 90s the main drawback wasn't the cost of the loudspeakers it was the cost of the crossover components. I wouldn't be surprised to find that the Dunlavy crossover has a thousand dollars worth of parts. But here in 2014, we can buy amp channels at Parts Express for $20 a channel, and we can do DSP filtering and delay for under $25 a channel thanks to MiniDSP. _See where I'm going with this?_ It wouldn't be that hard to do a five way or even a seven way. And the image would be HUGE but with pinpoint accuracy at the same time.

2) You can totally flip one of these arrays on it's side if you're careful with the crossover points. And to a large degree, that's basically what Opsodis is doing. It's taking Dave Smiths eXpanding Array and it's wrapping it around you.


3) Okay, here's The Money Shot. If you seriously have some time and money, you scale it vertically *and* horizontally. For instance, the Snell eXpanding array would be a 49x49 array if you scaled it in two dimensions.

Yes, you read that right, *NINETY EIGHT DRIVERS* for a stereo pair. And that might sound like a whacked out comb filtering nightmare, but it's not, because the design fixes the pattern flip.









If ninety eight drivers sounds completely bonkers for the home, you could always use it for PA use, and if you did, it would start to behave a lot like one of the Danley Jericho horns (which work on the exact same principles.) Here's a pic of the guts of one, it's definitely approaching that level of drivers. Must be lots of fun to wire up


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## Regus (Feb 1, 2011)

Orion525iT said:


> Why? I would encourage you to experiment. This just one idea, and you must be cognizant of the fact that this was set up in my living room; things may fall apart in actual application. I am also willing to except that there are problems that my ears cannot detect at this point. It takes time to train your brain to pick up on issues you don't notice the first time around. I can already think of 2 dozen or so variables to juggle, each with potential compromises.





Patrick Bateman said:


> Some people were wondering if putting the midbass behind you will work. It seems like a strange location. This actually *does* work, because the key is maximizing the interaural time delay.
> 
> 
> 
> ...


OK here goes.

Basically, a while back I was thinking that what was needed was a comparison between the different implementations of a midbass array with OPSODIS taken into account. My plan was to start with the simplest system you could build (i.e.one without processing) and see where it gets you, then look at what more you can do by adding some processing into the equation and/or adding more midbass speakers to realise the potentials benefits of a midbass array in conjunction with OPSODIS inspired speaker placement (I wasn't going to focus on anything other than midbass to start with as I see this as being the most likely part of the spectrum to benefit, at least for in car audio systems).

In practice, this basic system would be in some respects a retro-fit of the one Patrick talked about in the Jetta right at the start of the post i.e. tweeter, midrange and midbass, with midbasses as close to 180° separation and as wide as possible. In my current car, the stock locations are front bottom corner of front and rear doors, with tweeters on the wing mirror panel (pics to follow if required), so I was going to keep the stock locations, but improve on them by crossing the front midrange speakers over above the point where the rear door speakers are playing. Given the close proximity of the rear door speakers to the front seats, this would yields a near-optimum ITD for the midbass speakers.

There are a couple of issues that have held me back though. One was the choice of drivers for midbass - in an ideal world I'd like something that can play down into subwoofer territory to some extent (maybe half an octave below 80Hz), but this needs bigger drivers than are likely to fit in the stock location without serious modifications (cutting of sheet metal/door cards, reinforcement of the door, deadening, use of an enclosure in the door). The other alternative would be subwoofers that can play up into the midbass region, of which there are several, but I'm not sure I want to go that route, plus I'd still need some way to overcome the localisation cues from the subwoofers to the rear. Balanced against that is the thought that maybe I should allow for some overlap between midrange and midbass speakers, to incorporate at least some element of midbass array into the design, in which case there's likely to be more work required to get decent output from the front (there's a huge hole in the front door which is what's killing the output from the front with the stock speakers).

The second issue is amplification - even without processing, this is still adding up to quite a few channels if you want to get away from using passive crossovers for everything, which would be far less flexible in terms of determining optimum crossover frequencies, compared to using active crossovers, be they head unit or amplifier based or a combination of the two (as I said, this is meant to be a VERY simple system where it is primarily speaker position that determines how well it achieves its goal). Suddenly my simple system has become a much more complicated animal, analysis paralysis sets in and hence I have yet to start experimenting, in or out of the car, as I can't make up my mind where to start.

Orion525iT, thanks for your words of encouragement. Your previous posts above got me thinking I need to go down a slightly different route to that I originally had in mind, based on what seems like pretty convincing evidence that your approach is valid, but as you say, it's not necessarily the only way to get this concept to work, especially in light of Patrick's comments.

It's clear that I need to start somewehere so why not with choosing the midbass speakers that will go in the rear doors, as originally planned, followed by the subwoofer(s) to complement this choice in terms of placement and frequency range. Who knows, maybe I'll finally get around to installing my minimalists system and find less is more after all, so I should just do it and see what happens, as a true scientist would. Thought experiments are all very well, but only practical experiments will yield any hard data.


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## Patrick Bateman (Sep 11, 2006)

One dead-simple way of experimenting with this is to simply use computer speakers.










First, you go to Best Buy, or Wal Mart, or Target and you buy yourself two sets of cheap computer speakers. Now you have six drivers and six channels of amplification.









You put each sub where the midbass would go in an Opsodis setup.
You put two satellites where the tweeters would go.
You put two satellites where the midranges would go.

In order to keep the highs out of the midrange pair, just put a sock over the midrange. Preferable a wool sock. (Wool attenuates better than just about anything, even fiberglass.)


The fun part is playing with the location of the midbasses. If your experience is similar to mine, you will find that the size and the shape of the soundstage is largely determined by the midbasses, not the mids or the tweeters. IE, if you had a couple of stereo speakers seperated by two meters, *you'd get a big hole in the center of the stage.[/b But with Opsodis you can totally do this, then pull the midranges and the tweeters into the center to 'fill in' the hole. I have personally found that the 'trick' to all of this is getting the midrange and tweeter to a point where the hole is 'filled in', but not so close together that the stage is too narrow. It's a bit of a 'trial and error' thing.


But keep in mind, as long as you keep the original boxes you can return your $40 speakers to Best Buy when you're finished screwing around. Which of course would be terribly unfair to Best Buy, so don't do that, but you COULD...


*


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## Orion525iT (Mar 6, 2011)

Regus said:


> OK here goes.
> 
> Balanced against that is the thought that maybe I should allow for some overlap between midrange and midbass speakers, to incorporate at least some element of midbass array into the design, in which case there's likely to be more work required to get decent output from the front (there's a huge hole in the front door which is what's killing the output from the front with the stock speakers).


One point here. There is not an overlap between the midbass and midrange or between the midbass and the subs. However, one set of midbass is allowed to play *through* the midrange and is crossed to the tweeters. That is an attempt to keep things more simple. But lets face it, there is nothing inherently simple about any of this. You can only try to make things more simple. Trying to keep things simple is what led me to think about other arrangements that may work.

The most straight forward solution would be to mount big 'ol midbass at the ideal location. That is until you actually try to do it. There are many guys on here with tons of experience that have universally sworn off door mounted midbass, and for good reason.


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## Orion525iT (Mar 6, 2011)

Patrick Bateman said:


> I'm kinda curious to try varying the height to see if multiple midbasses can make the stage higher. IE, you don't want multiple tweeters because they're going to interfere with each other. But midbass frequencies are so long, you have a lot more freedom to vary their location. (As you found.)


I had to go back to this. I am curious as to what your reasoning is behind this. How would midbass impact stage height?


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## Patrick Bateman (Sep 11, 2006)

Orion525iT said:


> I had to go back to this. I am curious as to what your reasoning is behind this. How would midbass impact stage height?


Try this:

Get a couple of midbasses, set your crossover so that they'll cover about 80hz to 640hz.

Now vary their height. And tell me that it doesn't change the height of the stage. 

Here's why this works:

2khz is 17cm long. Due to the short length, our perception of it is dictated by pinnae cues. IE, if you have a couple of tweeters that are perfectly matched, your perception of their angle is basically determined by the shape of your ears. And this can be faked; you can EQ this.

But 500hz is 7/10ths of a meter. *This is a long wavelength.* So the shape of our ears tells us very little about where that sound is coming from. It's mostly determined by interaural time delays. *And due to that, it's REALLY easy to perceive the height of a midbass.* So a midbass in the bottom corner of a door is going to drag the stage down. And that's not the end of the world; there's no real reason that a stage needs to be at eyeball height.

But if you can create a bunch of midbass cues, by varying the height, your brain won't know where the midbasses are.



BTW, I'm screwing around with this right now. I have some midbasses I built that cover the two octaves from 150hz to 600hz.


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## Orion525iT (Mar 6, 2011)

^ Interesting.

When I had the midbass on the floor to my sides to approximate the Opsodis positioning, I thought I could detect some rainbowing. Again, I was not getting any cues from those midbass, I couldn't tell they were playing except for the change in the stage. I had fully convinced myself that the rainbowing was all in my head; I knew the midbass were on the floor.


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## Patrick Bateman (Sep 11, 2006)

Orion525iT said:


> ^ Interesting.
> 
> When I had the midbass on the floor to my sides to approximate the Opsodis positioning, I thought I could detect some rainbowing. Again, I was not getting any cues from those midbass, I couldn't tell they were playing except for the change in the stage. I had fully convinced myself that the rainbowing was all in my head; I knew the midbass were on the floor.


I was thinking about this today, and the ITDs shouldn't vary much with height. But I can *definitely* notice when I vary the height of the midbass enclosure. So that means one of two things:

1) high frequencies from the midbass are caussing pinnae clues
2) our brains can pick up the echo

I'm inclined to think it's #2. I've measured these midbasses, and their rolloff doesn't have any spikes in it. Or maybe it's something else entirely - but I can't think of anything off hand.


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## Patrick Bateman (Sep 11, 2006)

I built some dedicated midbasses for this setup, and I noticed that the maximum distance that you can put the midbasses is about one wavelength at the xover point. For instance, I'm using a crossover of 350hz*, and when the distance from midrange to midbass exceeds a meter, *I can detect where the midbass is.* But as long as it's within a meter, it 'blends' with the midrange.

* the maths :
sound travels 340 meters in a second, so it's (340m per sec / 350hz) = 0.97meter


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## req (Aug 4, 2007)

ok so looking at my setup where the midbass is just aft of my seat. within 12" of being perpendicular with my ears - the left midbass would be time aligned by a significant amount.

what are you thoughts about this alignment? it seems like this is the most practical use of the arrangement without building custom enclosures in the aft section of my doors or doing anything crazy. most poeple have the ability to install speakers in their rear door speaker location and it is usually fairly close to being 90* off axis...


i have not gotten the chance to do all that pink noise stuff you had discussed earlier - but i listened to the sublime self title album, and all the kick drum info is up forward in the front glass - but all the bass guitar is behind me, its a very strange thing to percieve.

i tried putting steeper slopes on the midbass and going to 150hz, even adjusting the eq down from 150~200hz but i still heard the 'bass guitar' type sounds coming from either direct left\right of my head or maybe from my headrest. like, slightly behind me. but everything else is up front.

i need to mess with TA\XOVER\LEVEL some more, and do some pink noise crap... so much work in tuning lol.


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## Patrick Bateman (Sep 11, 2006)

It seems like each driver needs to be within one wavelength of the next driver. For instance, with a three way, it would look something like this:

tweeter: 2khz - 20khz
midrange : 500hz - 2khz (Keep the midrange within 17cm of the tweeter, 2khz = 17cm)
midbass : 80hz - 500hz (Keep the midbass within .68 meter of the midrange, 500hz = .68m)

Basically you'll notice that the midbass needs to be relatively close to the midrange for this to work. If your midrange and tweeter are up high, then the front doors are about the only practical location. IIRC, the Volkswagen Golf had the midbass at the back of the door and the midrange at the front of the door or somewhere up near the A pillar. I'd have to read the thread again to confirm.

*If you go to a four way, things get easier.* For instance:

tweeter: 2khz - 20khz
midrange : 500hz - 2khz (Keep the midrange within 17cm of the tweeter, 2khz = 17cm)
hi midbass : 125hz - 500hz (Keep the midbass within .68 meter of the midrange, 500hz = .68m)
lo midbass : 33hz - 125hz (Keep it within 2.7m of the hi midbass)

^^ Those values are just a quick stab at it, but you can see that a four way makes it a lot easier to locate the drivers. It is likely the reason that Snell and Dunlavy have so many drivers in their arrays.

The David Smith paper would shed some light on this.


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## RocketBoots (Apr 16, 2011)

Also, I thought it was the case that cues from the higher frequency ranges greatly help 'place' midbass or sub-bass frequencies. Don't kick drums have a higher frequency for cues or 'attack', than bass guitar? [something like 6000 vs 800??] Which might help explain why instruments in a similar frequency range localize differently. You're getting cues for the bass guitar more from the midbasses located behind you.

To another point, midbass height shouldn't affect stage height, if we are to believe that our ears have a hard time placing things in the vertical plane. Isn't that the currently held belief?? I suppose the higher the midbass is crossed, the more it can be localized. I haven't tried this myself though.


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## Regus (Feb 1, 2011)

Quick question - I know I brought this up already in another thread, but in light of the observation that stage height can be affected by midbass height, is there any merit to my suggestion that we might want to consider installing a midbass speaker in the b-pillar? I've thought about it some more and it might be doable, something along the lines of a speaker mounted just below the window line (where the pillar tends to widen), using the same techniques to mount a speaker as for an a-pillar, just on a larger scale. The challenges are there in terms of making it a solid mount, enclosure volume for sealed versus venting into the frame of the car and not interfering with any critical safety systems in the area (seat belts, air bags, etc.). Size is also a consideration - can a large enough driver physically fit in this location or does it necessitate the use of a smaller driver (in multiples to get enough output)? Just thought I'd throw this idea into the mix one last time and see what happens...


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## Orion525iT (Mar 6, 2011)

Patrick Bateman said:


> I was thinking about this today, and the ITDs shouldn't vary much with height. But I can *definitely* notice when I vary the height of the midbass enclosure. So that means one of two things:
> 
> 1) high frequencies from the midbass are caussing pinnae clues
> 2) our brains can pick up the echo
> ...


After packing everything away, because I was tired of tripping over all the wires in my living room, I pulled it all back out and set up a test. At first I thought that any differences would be due to changes in ITD. To rule this out, I placed the midbasses at the same angle below and above ear level. I placed them ~1' below at a distance of ~3'. Then 1' above at the same distance.

Could I tell the difference? Absolutely. The stage did, in fact, seem higher with the higher placement. I could still detect a slight rainbowing with them in the lower position. 

The midbasses were crossed at 600hz, 24db/octave LR. I have no explanation for this; it absolutely flies in the face of conventional wisdom. Somebody else needs to try this.

Edit: Typed LW instead of LR (Linkwitz-Riley)


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## cajunner (Apr 13, 2007)

it could be that the artifacts of 2nd and 3rd order distortion is loud enough to create localization cues that don't fall in the catch-all of "10 db difference' maxim.

600 hz, 1200 hz, and 1800 hz, even if there are 24db/oct in place, pertains to the physical distortion, the electromagnetic properties.

and since we are supposedly most sensitive in this very region, it's hardly surprising that low mounted mid-woofers would bring the stage down in parts of songs, and rainbow effects aren't completely eliminated no matter how good the electronic parts are at fixing them.

the electric, can't overcome the physical and the electromagnetic together.


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## Patrick Bateman (Sep 11, 2006)

cajunner said:


> it could be that the artifacts of 2nd and 3rd order distortion is loud enough to create localization cues that don't fall in the catch-all of "10 db difference' maxim.
> 
> 600 hz, 1200 hz, and 1800 hz, even if there are 24db/oct in place, pertains to the physical distortion, the electromagnetic properties.
> 
> ...


I think we're picking up the echo and triangulating it. I have a pink noise track that pans across the stage, *and I notice that it's more "pinpoint" on the channel near a wall.* My hypothesis is that the wall is masking the echo (because it's so close to it, it blends with the initial wavefront.)










Here's a measurement of my midbass. The distortion is about 20-25dB below the fundamental in the passband. (Blue line is SPL, lower blue line is THD. Green line is an 8" Kef I compared it to.)


If anything, this is good news, as it seems to indicate we can raise the stage by raising the midbass. Maybe this is another one of the reasons that rear mounted midbasses don't work as poorly as you'd expect; in the rear quarter panels they're higher than they would be in the front doors.


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## Regus (Feb 1, 2011)

Orion525iT said:


> After packing everything away, because I was tired of tripping over all the wires in my living room, I pulled it all back out and set up a test. At first I thought that any differences would be due to changes in ITD. To rule this out, I placed the midbasses at the same angle below and above ear level. I placed them ~1' below at a distance of ~3'. Then 1' above at the same distance.
> 
> Could I tell the difference? Absolutely. The stage did, in fact, seem higher with the higher placement. I could still detect a slight rainbowing with them in the lower position.
> 
> The midbasses were crossed at 600hz, 24db/octave LW. I have no explanation for this; it absolutely flies in the face of conventional wisdom. Somebody else needs to try this.


Is there a reference track that we could all use for this or is pink noise sufficient?



cajunner said:


> it could be that the artifacts of 2nd and 3rd order distortion is loud enough to create localization cues that don't fall in the catch-all of "10 db difference' maxim.
> 
> 600 hz, 1200 hz, and 1800 hz, even if there are 24db/oct in place, pertains to the physical distortion, the electromagnetic properties.
> 
> ...


Would the use of an acoustic filter i.e. bandpass enclosure be a way of confirming that distortion is not the culprit?



Patrick Bateman said:


> I think we're picking up the echo and triangulating it. I have a pink noise track that pans across the stage, *and I notice that it's more "pinpoint" on the channel near a wall.* My hypothesis is that the wall is masking the echo (because it's so close to it, it blends with the initial wavefront.)


I'd like to hear more on this hypothesis of yours and also your thoughts on whether this would be as pronounced in a car as in a room with the speakers some way away from the source of the reflections. There is a significant difference in terms of height in a car compared to the average room, so maybe the triangulation would be less of an issue - presumably we could test this in a room if we could use something to absorb and attenuate any reflected energy, or find a narrow room where the speakers can be placed very close to the walls whilst maintaining the same degree of separation from the listener - I actually thought about using the under stairs cupboard as a "car simulator" (narrow width, sloping wall to the front) but it's too full if junk right now to do this!


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## Orion525iT (Mar 6, 2011)

Patrick Bateman said:


> If anything, this is good news, as it seems to indicate we can raise the stage by raising the midbass. Maybe this is another one of the reasons that rear mounted midbasses don't work as poorly as you'd expect; in the rear quarter panels they're higher than they would be in the front doors.


You already have me doing Opsodis(ish)and an array(ish), but it seems you want me to replace the rear quarter windows with midbass enclosures too 


Anyway, took a quick measurement with midbass in their enclosures from 100hz-2400hz. Maroon line is fundamental, black is THD.










Once I get the midbass enclosures for the front of the doors in place, I plan to mess around with placement of the Opsodis midbasses. All this in home experimentation and measuring is great and helps to test ideas, but in car things will change. 

BTW, I really like these Dayton PM180-8 for how I plan to use them. Smooth, but good detail.


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## Orion525iT (Mar 6, 2011)

Just tested out some stuff for about an hour.

Listened to _Another One Bites The Dust_, _Another Brick in The Wall_, and _Pawn Shop_ over and over.

I wanted to test the Opsodis midbasses behind me about 10". I was getting more output below 150hz in the midbass enclosures than I thought I would, so I moved the lowpass to 90hz 24db/oct LR on the sub manifold and highpass on all four midbasses to 100hz 24db/oct LR. I don't think I need to worry about stereo subs, I can go a more traditional route. 

I moved the Opsodis midbasses from 10" ahead, to 90 degree left and right, to 10" behind. Each location sounded different, but the stage did not appreciably pull forward or backward with each location. This is good! I actually preferred the midbasses in the postion 10" behind me. 

But again, 10" up or 10" down *did* change stage height. Again tons, and tons of variables to factor in. I did no eq, I don't think I even got the TA optimal. 

If it is an echo thing, I wonder if it makes a damn bit of difference in the car, as everything is near.


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## cajunner (Apr 13, 2007)

Regus said:


> Is there a reference track that we could all use for this or is pink noise sufficient?
> 
> 
> 
> ...



I'd say that you run into group delay issues with a bandpass, and the change in group delay may contribute or not at all, in enhancing all derivative distortion above the crossing frequency.


so, you deal with other problems at the same time as THD, and intermodulation distortion.


I personally don't experience much localization in a car below 300 hz, using test tones and well damped mounting locations.


this itself, flies in the face of convention and those golden ears who can localize 80 hz are possibly not aware of all the artifacts of a reproduction system contributing sounds above 80 hz, even if their crossover is believable and the system at lower volumes is highly defined.

I can probably attribute my lack of precision at 300 hz, to the average listening level I prefer to have my sound stage appear.

The louder it gets, the more the music takes on a "fill in all holes" quality, and the less particular I get over things like stage pull down, or to the rear.

and don't think of it as a neophyte's attempt at sound quality either, it's that same crosstalk that makes midbass palpable from both sides of the car, that also forces some destabilization of the image because of the higher distortion profiles of smaller diameter cones being made to play 300 hz and below.


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## Regus (Feb 1, 2011)

OK, how about this? If the midbass is crossed below the point it starts beaming, we don't need it on axis, so could we try listening to them off-axis and see if the localisation remains? I guess it depends on whether the distortion frequencies that are producing the height cues (if this is indeed the case) are attenuated off-axis or not - I've not looked into this in detail (beaming frequency versus diameter), I'm just brainstorming, so feel free to shoot holes in my argument. In any case, it would be easy to try this and see what difference, if any, it makes in practice. (N.B. I am planning to try out some OPSODIS experiments for myself, but I don't think I'll have an opportunity to do this until mid-August at the earliest).


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## Patrick Bateman (Sep 11, 2006)

Regus said:


> OK, how about this? If the midbass is crossed below the point it starts beaming, we don't need it on axis, so could we try listening to them off-axis and see if the localisation remains? I guess it depends on whether the distortion frequencies that are producing the height cues (if this is indeed the case) are attenuated off-axis or not - I've not looked into this in detail (beaming frequency versus diameter), I'm just brainstorming, so feel free to shoot holes in my argument. In any case, it would be easy to try this and see what difference, if any, it makes in practice. (N.B. I am planning to try out some OPSODIS experiments for myself, but I don't think I'll have an opportunity to do this until mid-August at the earliest).


I don't think beaming is a consideration at these frequencies. Phase dictates our perception at these frequencies, so the interaural time delay determines location.

That basically means that two midbasses to your left and to your right will have the widest stage, and the *depth* of the stage will be dictated by how far they are from you.

I keep posting this Opsodis pic, but they invented this, so I think they know what they're doing:



















The fact that the *height* of the midbasses makes a difference was unexpected. The frequencies are too long for the shape of our ears to make a difference, and ITD are barely affected by height. So that means that we're picking up the echo (my hunch) or we're insanely sensitive to ITDs.



To confirm if this is the case, try walking down a hallway with your eyes closed. Even with your eyes closed, *you can perceive that the space is small.* Methinks that perception is due to your brain picking up the echoes. Basically our perception of the size of the space is from those echoes.


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## cajunner (Apr 13, 2007)

Patrick Bateman said:


> I don't think beaming is a consideration at these frequencies. Phase dictates our perception at these frequencies, so the interaural time delay determines location.
> 
> That basically means that two midbasses to your left and to your right will have the widest stage, and the *depth* of the stage will be dictated by how far they are from you.
> 
> ...


what you call echoes, I call two through 5 order distortion.

and I think you're on to something here.

the "rules" as it pertains to ITD and intensity differences, is that there is no exact cutoff point, it's more of a general mound.... because we all have variable ear canals and the pinnae shape, etc. will determine where each of us rolls off.

A judge might be able to define a greater precision in your stage than yourself, because he has not only sharpened his "audio wits" but has natural ability based on genetics and physical traits.

this is going to sound funny, but I used to be a competitive pool player and I saw a few characteristics based on facial geometry and arm-eye coordination, that allowed me to assess whether I should attempt to up a bet or not.


being a good student of people, means you may erroneously depict a condition of a person, based on sample size, that is possibly true but may not be, haha..

anyways, this all pertains to whether or not my Optimum Sound Distribution, or whatever, is the same as yours.


what may seem like low playing woofers to one guy, may be entirely missed by another guy, and both guys are genius-level listening judges.

so let's not get too caught up in the minutiae, when we attempt to produce a wide AND deep stage for our maximum enjoyment. I have found myself becoming quite adept at using my own aural "fill in the blank" with pseudo-center, or phantom centers using horns, and I also enjoy the tight narrative of dash mounted midranges, it's all pretty much stereo at this point...


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## MetricMuscle (Sep 16, 2013)

So, is it safe for me to assume that one mid-bass in the front part of my front doors and one mid-bass in the front part my rear doors will sum to create the effect of one larger mid-bass to my 9 and 3 o'clock like a proper OPSODIS arrangement would have?

I will have time alignment to correct for the PLD from left to right but both left side mid-bass woofers will be on one channel and the right side will be on one channel so no T/A between same side front door and rear door.


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## Orion525iT (Mar 6, 2011)

MetricMuscle said:


> So, is it safe for me to assume that one mid-bass in the front part of my front doors and one mid-bass in the front part my rear doors will sum to create the effect of one larger mid-bass to my 9 and 3 o'clock like a proper OPSODIS arrangement would have?
> 
> I will have time alignment to correct for the PLD from left to right but both left side mid-bass woofers will be on one channel and the right side will be on one channel so no T/A between same side front door and rear door.


Ignore my previous reply, I miss read. 

I am not sure if you can get away with not having TA on all drivers. I would think that would be less than optimal. You could try, but physical placement will have a huge effect on outcome in my opinion.


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## MetricMuscle (Sep 16, 2013)

Orion525iT said:


> No, they will not "sum" in that way. The only thing that will get you Opsodis-like arrangement for midbass is Opsodis-like placement. You can't alter ITDs outside of physical placement.


I'm sorry but your answer does not support my idea and plan so I will choose not to accept it. 

The OPSODIS location will require me to cut my door panel, which I'm not 100% against, but I'll try my OE locations first and see how satisfied I am.

So even if the front door location and rear door location have equal path length to my ears it won't sum and work?


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## Orion525iT (Mar 6, 2011)

MetricMuscle said:


> I'm sorry but your answer does not support my idea and plan so I will choose not to accept it.
> 
> The OPSODIS location will require me to cut my door panel, which I'm not 100% against, but I'll try my OE locations first and see how satisfied I am.
> 
> So even if the front door location and rear door location have equal path length to my ears it won't sum and work?


Unless the rear door location is actually physically in a wider position, thus reducing the angle, to keep it at the same distance, I don't think you'll see any benefit (aside of more output). ITD will be the same. At that point, you might as well just do the front door location.

The reason TA is important is that it allows you to place the drivers at a reduced angle, without necessitating that they are placed at a physically wider position. The angle reduction increases the ITD, and distances can be whatever. Ideally you want them wide and at reduced angle, but a car is only so wide, and the doors only so deep.

I would not think of it as summing really. It's a possible cheat to be able to place smaller drivers at a more favorable Opsodis-like position, with the hope that precedent effect masks the less than ideal positioning, and less than ideal ITD of the additional (front of door, ect) midbasses. Additional benefits may be "spreading of the chaos" and more output. 

Again, this is mostly hypothesis at this point. The testing I did inside seemed to confirm and hold promise, but that may change in actual application. I wouldn't go hacking my car to bits, unless I really wanted to try something different.


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## Patrick Bateman (Sep 11, 2006)

MetricMuscle said:


> I'm sorry but your answer does not support my idea and plan so I will choose not to accept it.
> 
> The OPSODIS location will require me to cut my door panel, which I'm not 100% against, but I'll try my OE locations first and see how satisfied I am.
> 
> So even if the front door location and rear door location have equal path length to my ears it won't sum and work?












In my car the stock location in the rear door is a *little* bit better.

Main downside is that I would have to do a four-way to make it work, because the distance from the front to the back is so far.

Also, ignore the speaker in the trunk, I made this illustration for another thread.


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## traceywatts (Jun 2, 2008)

req said:


> i think the biggest problem with horn loading a midbass that is in-line with your hip area in a car is physically putting it there. even if you can mount it under the seat and squirm the throat\mouth up the B pillar it would still be extremely dificult - and most likely a 1-off thing that is not very easy to modifiy and perfect.
> 
> personally, putting a solid midbass in a rear-door that is deadened properly and crossed around 300hz is a very simple way to achieve the added width.
> 
> ...


I couldn't attach the graphic, but the opsodis frequency vs angle graph shows that a single-driver frequency response of 300-5k would not be optimal (it hits red zones). Since I have read similar xo points for several opsodis attempts IN THIS THREAD, I am thinking that this may be partly responsible for some of the 'poor' results...


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## BillC (Feb 26, 2017)

Interesting, installing speakers in my 2008 Jetta soon and it has the same door setup. Currently have a cheap set of cadence qrs6k3 3 ways ran off 2 channels of an alpine pdx-4.100 and an alpine cda-9887 and it really does stage amazingly well for as simple and cheap as it is.


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## Regus (Feb 1, 2011)

This whole concept still intrigues me, at least the concept of the midbass speakers being placed to the left and the right of the listener with 180° separation. There's a great deal to consider in terms of implementation and I plan to re-read this thread and summarise exactly what is required to successfully implement this kind of setup.

It occurs to me that other than the VW Jetta in the original post, a coupé (or any other car without rear doors) really lends itself to this kind of an installation - you could get close to the ideal 180° separation relative to the listening position by installing the midbass speakers in the side panels just behind the rear seats, as in the following image:

https://images.app.goo.gl/px8eQc5baqbrhv5x9

It seems to me that you could fabricate a sealed enclosure for a midbass in this location, and whilst not as close to 180° as the location of the midbass in the door of the Jetta, it might be worth it to be able to use a sealed enclosure, which is difficult to implement in a door . I also think it would be very interesting to see whether going slightly beyond 180° is better or worse than midbass speakers at the front of the doors (or in the kickwell).


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## req (Aug 4, 2007)

Regus said:


> VW Jetta in the original post, a coupé (or any other car without rear doors) really lends itself to this kind of an installation
> 
> fabricate a sealed enclosure for a midbass in this location


i think it works well 

https://imgur.com/a/T68gRmr


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## Patrick Bateman (Sep 11, 2006)

Ugh I'd love to hear that. I've been thinking about getting a GTI to replace my lame-mobile. (Mazda CX5)


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## req (Aug 4, 2007)

Patrick Bateman said:


> Ugh I'd love to hear that. I've been thinking about getting a GTI to replace my lame-mobile. (Mazda CX5)


unfortunately it was flooded and totaled. but im making something new right now...


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## tshephard (May 27, 2018)

yeah, yeah, dead post, etc....

Anyway - I'm looking at this, the pics/graphs in detail, and reading other sites
and
just cannot read/figure exactly what the crossovers are - I'm guessing on this graph, going to the next seems different. etc.

So, anyone have any formulas from the work?

I'm in a modern Challenger, front doors are de-tweetered 62ix's, dash at A pillars are de-tweetered 4032cfx's, and the center tweets are from the 62ix so far.
Using 4 channel amp, doors, then dash and center, each 75-80 watts or so - not getting close to that.
So far, I'm very pleased with image centering - 'blind test' very close to center on balance knob, and head swivel maintains image.

So, getting down to final crossover parts order.
Seems like between 250 and 600 for Bass/Mid crossover - depending on where I look for data.
Seem like 3300 or so for for Mid/Tweet crossover - depending on where I look for data.

I do see references to formulas, seem to be based on distance from centerline and frequency - anyone parsed that out?

THX, any, all


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## Patrick Bateman (Sep 11, 2006)

I wrote this post over seven years ago, but here's a summary, as I recall it:



The way that our hearing mechanism works, if you are too close to one speaker, the soundstage will collapse to one side (this is pretty well understood.)
At lower midrange and midbass frequencies, our perception of location is based on differences in arrival times, NOT amplitude. For instance, if you fiddle with the balance knob on your car stereo, it doesn't make any noticeable improvement in the soundstage location _when the frequencies are below about 700Hz or so._ And the importance of arrival time becomes increasing important as frequencies go lower. This leads to a strange conclusion: if you must sit too close to the midbass (like if you're sitting in a car) it may be superior to have the midbasses at 9' o clock and 3' o clock.










A picture is worth a thousand words, so here's a pic.

Here are three different speaker locations. Note how having a midbass directly in front of you is a "worst case scenario", for soundstage width. Basically the sound arrives at both ears simultaneously. If the speaker is at 9 o'clock, the difference in time arrivals is maximized. (The arrows in the diagram illustrate the distance from one speaker to your LEFT ear and to your RIGHT ear.) A speaker location at 10 o'clock or 11 o'clock splits the difference between maximizing stage width and minimzing stage width.

Of course there's No Free Lunch, so this setup comes at a price: *stage depth.* Obviously, if you put your midbasses at 9 o'clock, the depth of stage will suffer.

So a lot will depend on whether you prefer a deep but narrow stage, or a wide stage that's "in your face."










To me, the thing that's interesting about this geometry, is how it varies with frequency. IE, the higher in frequency that you go, the more you want to have your high frequencies coming from far away, and probably in the center! This flies against common wisdom: most people put their tweeters as wide as possible. This is backwards: it's actually the MIDBASS that benefits from wide placement.

If you don't believe me, you can play around with this experimentally. If you have tweeters that you can move around in the cabin of your vehicle, try bringing them progressively closer together. IE, if the tweeters were in your doors or in your A-Pillars, try moving them onto the dash. Then try bringing them closer and closer together.

What you should hear, is that the _width_ of the soundstage doesn't change. This is because it's the lower midrange and midbass frequencies which tell your brain how wide the stage is. The key to all of this, is that _our perception of soundstage width and depth is largely determine by midrange and midbass location. _Try it yourself, and see what you think. And if you agree, then you have the freedom to put your tweeters in some rather strange locations. Taken to an extreme, you might even use a single tweeter, placed in the center, and as far back as you can place it.










That solution is rather extreme, and you'll probably get best results if you split the sound into bands, with highs in the middle, then midrange, then midbass. This is fractal in nature; you could do a ten way if you were so inclined! 

Make sense?

If you do this experiment, be sure to put the tweeters on some type of device to keep them away from a boundary. IE, you don't want to place them ON the dash, because that will create early reflections which will muddy everything.










Something like this is better than simply placing them on the dash, unless you have the ability to flush mount them, which is even better.


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## Patrick Bateman (Sep 11, 2006)

In regards to crossover points:

If I were going to fiddle around with this, here's where I would start:


First off, I'd probably start by going with a mono supertweeter. When messing around with Opsodis, a mono supertweeter seems to deliver the most "bang for the buck." The reason for this, is because ultra high frequencies are so short. 10khz is 3.4cm long (1.35") Because 10-20khz is so short, what happens is that your LEFT tweeter interferes with your RIGHT tweeter in a stereo setup. IE, if your left tweeter is playing 10khz and your right tweeter is playing 10khz, if you move your head by a whopping 1.7cm (0.675") _the sound will be out of phase!_ If you've ever measured a speaker in mono, then measured a pair in stereo, you'll see this phenomenon. Basically the left and the right tweeters interfere with each other in a huge way. Due to this, a SINGLE tweeter may sound superior than a _pair_ of tweeters. Give it a try and see what you think.

One warning though: To do this, you'll need a processor that can turn a stereo signal to mono. MiniDSP has a plugin for a 2.1 system that can do it. The plugin is designed for a mono sub, but there's nothing stopping you for using it for a tweeter. (Change the xover point, obviously)

Another warning: Due to the way that some albums are mixed, you may find that some producers _intentionally _invert the left and the right tweeter. They do this for artistic reasons - it makes the stage sound wider. If you run into one of these recordings, it will sound weird in mono. (If you sum two out-of-phase signals, you get silence.) In that situation, the only practical solution is to run TWO supertweeters, fairly close to each other, with a waveguide. Like this:










Realistically, this is probably the easiest / most practical solution to the Mono Tweeter Dilemna. Note that even a very VERY small waveguide will work for a supertweeter. Even a diameter of 1.5" should suffice. (10khz is 1.35" long, so even a tiny waveguide will help.)


I personally think that the location of the midrange is the most important. IE, if you want to do opsodis, you probably want to use three channels, _minimum_, because the location of the midrange is critical. Basically put it in the most optimal location you can find in your car.


Locating the mid-bass is probably the fun part. Because once you go Opsodis, you can put the midbass in some really bizarre locations. You're no longer relegated to putting it in the front of the door, or in the kicks. You might put it in the floor, or under the seat, or in the front of the REAR doors of your sedan, or in the rear quarter panels of a coupe, or even on the rear deck! The KEY, is that you want it as wide as you can get it. (Because midbass width will largely determine soundstage width.) I personally have my midbasses under my seat. I have them in bandpass boxes. I do this because a bandpass enclosure filters out the harmonics. And harmonics can 'give away' the location of a midbass. For instance, if your midbass is playing 100hz, it has 2nd harmonic distortion at 200hz and 3rd harmonic at 300hz. The 2nd and 3rd harmonic can give away it's location. We just want to hear / perceive the fundamental, not the distortion. The other advantage of bandpass midbasses is that you can orient the port of the enclosure to maximize soundstage width. Taken to an extreme, you could even move the port somewhere else. Bose did this in the Mazda RX-7.


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## tshephard (May 27, 2018)

Well, hey, thx!
I'll read slowly and digest for a bit.
My tweeters are the 62ix's, on a seperate wire, through a cap, driven with the mids at the dash A's. As yet, they are laying about 6 inches apart at the center dash, near the hood - and it works so far.
The single main thing I was after was a duplicate stage for the wife - this seems 95 - 98% there.
Again, THX.


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## tshephard (May 27, 2018)

OK, had a chance to digest and do some work.

1 Supertweets - My budget is spent, I have what I have for 'major' components. I do have those tweeters from the 62ix's installed, with just a 10 mF for a 'safety' block - should be good for about 5.3 kHz. Based on my own testing, I cannot hear above 6k. Regardless, I ordered 2nd order crossover stuff at 3.3k - the best I could read the log graphs and select common parts. So center dash dual tweets will start at 3.3k, and the A-dash mids will end at 3.3k. Any better way to chose mid-tweet xover for this scheme - a distance formula?

2 Mids - Again, 600 seemed to be the best I could read log graph, and with parts availability that ended up at 1st order at 540 for ending Mbass and starting Mids at A-dash. Distance or angle formula, other's test data?

3 Mbass - doors, free at low end, out at 540 (there will be no sub). They are very well mounted, coupled to the card with foam, feel like 2 fans!

4 I started this as my second wack at good 2 seat balance. Some of the later online files' graphics show 2,3,4 seats with balanced sound - I'm hoping, early prototype seemed to suit me.

THX for playing along!


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