# Space: The Final Frontier



## Patrick Bateman (Sep 11, 2006)

For the better part of this year I've been knee-deep in a supercomputing project at my day job, so haven't had a lot of time to post any new projects. But as usual, my stereo is incomplete, so thought I'd use this thread to document a new project 

Like the previous projects, this project is going to build on the projects that came before it. All of my projects from the nineties were tuned by ear, and while they did a few things well, very few of them were satisfying in the long term. In 2006 I set up a proper measurement lab, and that took my projects to the next level. Learning how to use a mic enabled me to fix the problems with my projects, and after three years of practice, I've found that 75% of the issues with my stereos can be fixed with judicious use of measurements to tailor the sound.

*But that leaves the last 25%.*

So that's what this thread is about - using some subjective tricks to tailor the sound.

So here's the goals for this project:


In one of my recent projects, I discovered that the conventional location for tweeters may be wrong. I was able to get a wider and deeper soundstage by bringing the tweeters _closer_ together, and found that the depth of the soundstage was improved by bring the tweeters _forward._ This is completely counter-intuitive, and I wouldn't have stumbled across the idea if it wasn't for a master's thesis that I stumbled across.*
Most of my major projects for the past few years are variations on a Unity horn. After three years of messing around with them in the car, I'd say i'm 75% certain I won't be using them again. It's not that they're bad, they're just too big for a car. I think we can get 75% of their advantages in a smaller package.**
I believe that line arrays and dipoles offer some advantages in the car, and I'd like to explore them further. Kudos to Wehmeyer and Winker from JBL for cluing me in to these.

Anyways, stay tuned, this project will be more accessible and quite a bit different than what came before it. If you'd like to review my previous projects, here's a couple:

* The project that got me thinking about unorthodox tweeter locations: http://www.diymobileaudio.com/forum...rum/72891-anyone-tried-using-one-tweeter.html
** I've put five Unity horns in the car. (I lost interest in two of them before finishing.) This project will be similar, but less expensive, easier to build, and better looking. Here are the first and the last:
Twelve Inch Woofers In My Dash - CARSOUND.COM Forum
http://www.diymobileaudio.com/forum...forum/71993-unity-v-midbass-strikes-back.html


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## funkalicious (Oct 8, 2007)

Subscribed. Always love to hear your thoughts on audio.


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## Patrick Bateman (Sep 11, 2006)

To give you an idea of what this project is going to look like, here are a few links.

First off, here's a pic of one of my Unity horn projects. The Unity horn behaves a lot like a coaxial speaker, except with much higher power handling and efficiency, and exceptionally low distortion. They're one of the most complex loudspeakers you'll ever come across, unfortunately. Not for the faint of heart. Kudos to Danley for being so generous with the information on how he makes them work.






This is the fifth of my unities, not finished. You can see the coaxial mounting of the tweeter, the woofer, and the midrange. In a "real" unity horn there's four mids and four woofers, which is obviously impractical in a car.







Here's a D'Appolito array with a waveguide loaded tweeter at the apex. This particular speaker is from YG Acoustics, and retails for $28,000. I evaluated it in 2005 at the Rocky Mountain Audio Fest, but preferred the sound of the Gedlee Summa. (Which I ended up purchasing three years later, and serves as my reference.)

The advantage of the D'Appolito array is that it reduces reflections off the ceiling and the floor. The waveguide creates a better match with the woofers than a direct radiator.







This is a Snell "eXpanding Array." It's a clever refinement of a D'Appolito array. Basically, it uses a different combination of crossover slopes and spacing to get a MUCH better directivity pattern and off-axis response than a D'Appolito array.

David Smith, the inventor of the expanding array, posted some comments on my analysis of his speaker here:
D'Appolito Arrays with Waveguides - diyAudio

My project is going to look a lot like the last speaker, but all three of these speakers have something in common. In a lot of ways, all three act like a true point source.


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## lycan (Dec 20, 2009)

sounds like fun 

Here's a clue as to why moving tweets _closer_ toward the center may increase width, and why moving tweets _further in_ from the windshield may increase depth:

_What happens to the *image* drivers, when we move the *primary* tweets in these directions?_

Remember ... we're always positioning and aiming WAY more than two tweets in a small, reflective environment  Keeping this in mind, things that are counter-intuitive at first glance start to make lots more sense 

Also, on a side note, the primary advantage of the D'Appolito array discussed in his first paper is : zero lobing error on-axis, independent of the chosen crossover. Lobing error is the "slope of the lobe", and the vertical symmetry of his array guarantees that this will be zero, no matter what crossover slope or alignment is used to cross to the tweet. This advantage quickly disappears, though, as the listener moves vertically off-axis ... as anyone who has listened extensively to D'Appolito alignments can quickly verify!

Reduced reflections in the vertical plane are an additional benefit.


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## rawdawg (Apr 27, 2007)

lycan said:


> _What happens to the *image* drivers, when we move the *primary* tweets in these directions?_


I'll take a stab.... The relative position of the "image drivers" widen in respect to the primary tweeters. I'll also guess that the "phantom tweeters" also widen and deepen with the move.


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## lycan (Dec 20, 2009)

rawdawg said:


> I'll take a stab.... The relative position of the "image drivers" *widen* in respect to the primary tweeters. I'll also guess that the "phantom tweeters" also *widen and deepen* with the move.


i doubt you're "guessing" ... but you're correct in any case  The "phantom tweeters" ARE the "image drivers" 

This ain't some esoteric, academic study of audio by the way ... you don't need a PhD in acoustics to look at an image in a mirror, and watch the way _reflections_ move, as the primary object moves  Those reflections are the "image sources", just as "real" as the primary tweets (for frequencies where the tweets are radiating in all directions). Remove the glass/mirror, put secondary tweets where those phantoms are, and you've got the same acoustic field inside the vehicle.


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## Se7en (Mar 28, 2007)

Lycan,

I'm assuming that due to the reduced number of reflections we are getting a greater ratio of direct sound to reflected sound (good) and ultimately less reflective interaction with the boundaries of the vehicle (at least that our ear/brain would localize).

Also, that due to the fact that these tweeters would typically only handle frequencies above 2khz, and that those frequencies are primarily responsible for height cues only (which are also mono). Lastly, that those frequencies fall into the realm of IID and not ITD, meaning that we're far less sensitive to how close or far they are from our ears.

What else am I missing. School me.

Edit: Disregard, I just read your last post..


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## rawdawg (Apr 27, 2007)

Whoops! I thought by "Image drivers" you were referring to the drivers that handle the ITD range ie; the midbass speakers. Thank you for the clarification.

To all, forgive me for the thread jack(but I do believe it is partially on topic), is the center tweeter location valid for super tweeter duties?


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## lycan (Dec 20, 2009)

Se7en said:


> Lycan,
> 
> I'm assuming that due to the reduced number of reflections we are getting a greater ratio of direct sound to reflected sound (good) and ultimately less reflective interaction with the boundaries of the vehicle (at least that our ear/brain would localize).
> 
> ...


no problemo 

Just remember, you think you've only got TWO tweeters ... in fact, you've got at least EIGHT tweeters that you're positioning and aiming.


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## vactor (Oct 27, 2005)

this is a good read with respect to why moving high frequency sources closer together might lead to improvements in the soundstage and perception of depth and width ...

Virtual Acoustics and Audio Engineering: Stereo-Dipole


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## ErinH (Feb 14, 2007)

moving the tweeters closer to you should lower reflections. I would assume that's why you feel you have a better soundstage. 


just dropping in...


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## lycan (Dec 20, 2009)

vactor said:


> this is a good read with respect to why moving high frequency sources closer together might lead to improvements in the soundstage and perception of depth and width ...
> 
> Virtual Acoustics and Audio Engineering: Stereo-Dipole


not exactly "on-point" though ...

That research (as i recall) was mostly based on sound reproduction with technologies _other_ than basic stereo ... namely, reproduction technologies based on crosstalk cancellation (in basic stereo, there is no crosstalk _per se_, as blumlein stereo requires _both_ speakers to be heard by _both_ ears). The classic, historical problem with crosstalk cancellation technologies has been an _extremely_ small sweet-spot ... move your head a little bit, and the crosstalk cancellation goes to hell quick (especially at higher frequencies, shorter wavelengths). The phrase "head in a vise" was coined around one of these technologies, as i remember.

What this research does is investigate a crosstalk cancellation technology with higher-frequency drivers placed closer together, to minimize the tiny sweet spot problem.

Not necessarily applicable, at least directly, to basic stereo.


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## 14642 (May 19, 2008)

It's not eight tweeters or even 16 tweeters. It's millions and billions of tweeters. Consider the polar response of a 1.5" diameter tweeter:










This thing BEGINS to narrow at 12.5k. Everything below that radiates into almost all forward angles. If you mount the tweeter in the door panel, A-pillar, or dashboard, then all surfaces reflect EVERYTHING below abotu 12kHz. If you move the tweeter away from the "baffle" and suspend it in the air, you'll reduce the reflected energy a bit and delay the earliest reflections, but you'll reduce the delay for later reflections (the ones that reflect off surfaces closer to your ears, like the side window). 

Maybe I can dig up some impulse response measurements I made a long time ago. Making those measurements in a room often reveals reflections that are easy to identify. Typically the floor provides the first one, ceiling or side walls the second, third and fourth. Reflections from two or more surfaces (before reaching the microphone) are often reduced enough in level that they don't affect the image, but they do define the size of the space. 

This same stuff happens in a car, but the reflections arrive much sooner and are much louder because the surfaces are so much closer. It's nearly impossible to pick peaks and assign them to surfaces. The near side glass is about the only one I've ever been able to identify reliably. All of this work to minimize or use the reflections is kinda like pulling weeds in the jungle.


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## lycan (Dec 20, 2009)

Andy Wehmeyer said:


> It's not eight tweeters or even 16 tweeters. It's millions and billions of tweeters. Consider the polar response of a 1.5" diameter tweeter:
> 
> 
> 
> ...


dude, i know it's more than eight ... just getting a point across, is all 

I just counted the FIRST reflection from : left side window, right side window, and front windshield. At some point, the intensity will drop enough to be ignored, and the delay will exceed the Haas limit. So it might be more than eight ... but probably not _millions_ 

But i always laugh at those that advocate "on axis" positioning of the tweeters ... exactly which of the eight-plus tweeters are you pointing "on axis" ???


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## ItalynStylion (May 3, 2008)

So what we need.....is laser tweeters


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## 14642 (May 19, 2008)

OK. I found an impulse response measurement. This is the OE speaker in the driver's door of a Mini Cooper with the microphone in the driver's seat. The two graphs are the same measurement shown at two different resolutions. As I wrote earlier, have fun picking peaks and identifying reflective surfaces.


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## 14642 (May 19, 2008)

And here's a near field measurement (without the reflections form the inside of the car) of the tweeter from the same door at a couple of different resolutions. If you compare this with the measurements in the earlier post, it's pretty easy to see just how insurmountable the reflection problem is if your objective is either to control them or eliminate them. The best way to deal with this is to design a speaker system where the off axis response is as similar to the on axis response as possible and just EQ the whole thing at once. Room correction and speaker correction are the same thing in a car. There's no reverberant field and the vast majority of the reflections are within what we hear as the original sound.


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## 14642 (May 19, 2008)

OK. Let's put these side by side, so it's easier to compare. These two are about the same resolution. The first one is the impulse response of only the tweeter without the reflections. The second one is the response of the tweeter and the mid in the door measured at the driver's seat. The difference between the two are reflections and the low frequencies contributed by the midrange. The flat spot before the impulse in the second one is the time it takes the sound to get from the speaker to the mic. It's easy to see that the mic is much closer to the tweeter in the first measurement. Don't be too distracted by the fact that the second measurement includes the mid. The very sharp peaks in the second one are high frequency reflections. 




















OK, so upon further analysis, it appears that the peak at .0049 is probably a reflection off the windshield (includes a little more low frequency information than the one at .009, so it's likely the lower range of the tweeter's response). The one at about .009 is the reflection from the passenger's side window and is mostly really high frequency. The rest are really difficult to identify, but if you want to try, pick each peak, determine the distance from the speaker to the reflecting surface and then to the microphone by subtracting the time of the initial impulse (about .00215) from the time of the peak that you choose and then multiplying that by 1132ft/sec. Once you know the distance, you can go searching around the car with a tape measure for a reflection from the speaker to the mic that has a pathlength that corresponds to that distance. Then, once you've mapped all the reflections,you can try to eliminate them by changing shapes, adding foam and carpet, etc. Or you can go play whack-a-mole with a 3rd-grader. 

Speakers with narrow dispersion will eliminate some of the reflections from adjacent boundaries, but it's pretty easy to see here that those are only a small part of the problem.


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## ItalynStylion (May 3, 2008)

This may be a silly question (or two) but I have to ask because I intend to learn.

What do these reflections sound like? I'm aware that they are additions to the sound and are undesirable but what should you be listening for? What are the most problematic mounting area and which is the least (on average) with respect to this topic?

Also, if the music you are reproducing on the speakers were happening in front of you, live, there would still be reflections correct? If any room were completely devoid of all reflections, like an anechoic chamber, it would sound totally unnatural wouldn't it? This would lead me to believe that at least SOME level of reflections is desirable no?


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## 14642 (May 19, 2008)

ItalynStylion said:


> This may be a silly question (or two) but I have to ask because I intend to learn.
> 
> What do these reflections sound like? I'm aware that they are additions to the sound and are undesirable but what should you be listening for? What are the most problematic mounting area and which is the least (on average) with respect to this topic?
> 
> Also, if the music you are reproducing on the speakers were happening in front of you, live, there would still be reflections correct? If any room were completely devoid of all reflections, like an anechoic chamber, it would sound totally unnatural wouldn't it? This would lead me to believe that at least SOME level of reflections is desirable no?


Ahhh...the right questions. 

Because these reflections all happen very soon after the initial sound, they sound like frequency response anomalies--peaks and dips in the response. The early ones spread the apparent source and the ones toward the end help us determine that we're in a small space. The reflection from the left speaker off a boundary on the right that arrives at our right ear and vice versa is crosstalk. That crosstalk narrows the image and degrades the stereo reproduction a little bit. 

In a big room or a concert hall, the walls are farther away and the reflections arrive at our ears much later and with reduced intensity. many of them sound like separate events--that's reverberation. We can make the space in the car seem larger by ADDING late reflections and some additional early ones. Trying to get rid of the ones that are there is a waste of time. As Patrick has discovered, the size of horns that are required to narrow the dispersion enough to make a difference is prohibitive in a car.

Reflections are how we determine the size of the space we're in. Listening to speakers in an anechoic chamber is horrible--the most unnatural sounding thing you've ever heard.


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## ItalynStylion (May 3, 2008)

Andy Wehmeyer said:


> Ahhh...the right questions.
> 
> Because these reflections all happen very soon after the initial sound, they sound like frequency response anomalies--peaks and dips in the response. The early ones spread the apparent source and the ones toward the end help us determine that we're in a small space. The reflection from the left speaker off a boundary on the right that arrives at our right ear and vice versa is crosstalk. That crosstalk narrows the image and degrades the stereo reproduction a little bit.
> 
> In a big room or a concert hall, the walls are farther away and the reflections arrive at our ears much later and with reduced intensity. many of them sound like separate events--that's reverberation. We can make the space in the car seem larger by ADDING late reflections and some additional early ones. Trying to get rid of the ones that are there is a waste of time. As Patrick has discovered, the size of horns that are required to narrow the dispersion enough to make a difference is prohibitive in a car.


Interesting. For competition is there any type of rules about putting foam pieces in the window recesses? I bet that would help a lot. I realize it wouldn't kill all the reflections but it would reduce them I'd think. Possibly to the point where they would simulate a larger room.



Andy Wehmeyer said:


> Reflections are how we determine the size of the space we're in. Listening to speakers in an anechoic chamber is horrible--the most unnatural sounding thing you've ever heard.


I still want to try it one day.....just to experience it


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## Mic10is (Aug 20, 2007)

ItalynStylion said:


> Interesting. For competition is there any type of rules about putting foam pieces in the window recesses?


front windows which include driver and passenger windows and windshield cannot be covered on the inside by any materials. This is true for all organizations.
MECA allows you to cover the outside to reduce judging distractions (ie..hot girls with a nice ass walking in front of you while you are supposed to be focusing on Rebecca Pigeon)

rear windows can be covered.

MECA has restrictions on which classes can use acoustic treatments as well. I do not think classes below Mod-ex can use much acoustic treatment.


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## ItalynStylion (May 3, 2008)

Cool, thanks for the clarification man!


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## lycan (Dec 20, 2009)

Andy Wehmeyer said:


> Ahhh...the right questions.
> 
> Because these reflections all happen very soon after the initial sound, they sound like frequency response anomalies--peaks and dips in the response. The early ones spread the apparent source and the ones toward the end help us determine that we're in a small space. The reflection from the left speaker off a boundary on the right that arrives at our right ear and vice versa is crosstalk. That crosstalk narrows the image and degrades the stereo reproduction a little bit.
> 
> ...


I largely agree, but a few points are worth emphasizing :

1. Very near, close-in-time reflections will NOT be distinguished from the original sound (the Haas limit determines how close is "close"). They will impact frequency response (via comb filtering) and localize-ability ... mostly, never in a "good" way: stereo reproduction, from recording through expected playback, does not "depend on" nor "anticipate" these reflections in any way. There are a few exceptions, where near reflections aren't a terrible thing, including : ultra-close reflections, such that the first comb null is outside the driver's pass band (categories include corner-loading subs, and midranges on dash very close to windshield), and deliberately depending, primarily, on a tweeter reflection, while minimizing that tweeter's primary radiation to the ear.

2. Later-in-time reflections do indeed give us a sense of "space". The mind _can_ distinguish these (even if just barely) from the original event. This category was the whole basis for "intelligent rear fill" ... bandlimited, _delayed_, L-R difference signal. Done properly, this technique will give you a larger sense of space, sounding like you're listening in a larger-than-shoebox venue.

3. Very late reflections sound like reverb or echo ... mostly to be avoided.


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## 14642 (May 19, 2008)

lycan said:


> 3. Very late reflections sound like reverb or echo ... mostly to be avoided.


Avoiding these in a car isn't too difficult. there's no possbility thatyou could mount a speaker far enough away to generate these and no reflective surface is far enough away to provide them.

I find, though, that adding some that are synthesized by a DSP can have a really pleasant effect and can dramatically increase the sense of space, but they don't extend the width of the instrument placement. Early reflections (like ones you'd hear from the wall behind and beside the musicians) can also be added in the same way and also have a pleasing effect.

If you're in LA, I'd be happy to give you a demo, but I think this may be the only place to hear this. My car includes some custom DSP that does this, but I've never heard another car that includes it.


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## lycan (Dec 20, 2009)

Andy Wehmeyer said:


> Avoiding these in a car isn't too difficult. there's no possbility thatyou could mount a speaker far enough away to generate these and no reflective surface is far enough away to provide them.
> 
> I find, though, that adding some that are synthesized by a DSP can have a really pleasant effect and can dramatically increase the sense of space, but they don't extend the width of the instrument placement. Early reflections (like ones you'd hear from the wall behind and beside the musicians) can also be added in the same way and also have a pleasing effect.
> 
> If you're in LA, I'd be happy to give you a demo, but I think this may be the only place to hear this. My car includes some custom DSP that does this, but I've never heard another car that includes it.


A couple doods on this forum have had some success with our "dumb" (well, "dumb" by MS-8 or Logic7 standards ) technique for rear fill, or "ambience recovery" : form the L-R difference signal, bandlimit the treble and low-bass out of it, and delay it ... by about 20msec, just this side of echo or reverb. Probably nothing as fancy as what you're doing, but ain't half bad either, for creating a larger "sense of space" without degrading the front stage 

As much as i hate to admit it, i'm overdue for a trip to LA  Can you do something about the traffic in the next couple weeks?


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## 14642 (May 19, 2008)

lycan said:


> A couple doods on this forum have had some success with our "dumb" (well, "dumb" by MS-8 or Logic7 standards ) technique for rear fill, or "ambience recovery" : form the L-R difference signal, bandlimit the treble and low-bass out of it, and delay it ... by about 20msec, just this side of echo or reverb. Probably nothing as fancy as what you're doing, but ain't half bad either, for creating a larger "sense of space" without degrading the front stage
> 
> As much as i hate to admit it, i'm overdue for a trip to LA  Can you do something about the traffic in the next couple weeks?


Yo, Hairy night creature,
Traffic here isn't any worse than I-35. I'll buy the beer. FLy into Burbank and there's no traffic. 

Yes, your method works pretty well too. That 20mS delay is pretty common for these kinds of systems and that's what the rear channel delay is in MS-8's Logic7. That's not all that happens, but that's part of it.


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## ErinH (Feb 14, 2007)

Andy Wehmeyer said:


> Reflections are how we determine the size of the space we're in. Listening to speakers in an anechoic chamber is horrible--the most unnatural sounding thing you've ever heard.


which brings up something I've wondered from time to time: how much is too much?

A lot of the reason we car audio guys harp on reflections is because it detracts from a focused image. We do what we can to tame it, but given the fact that there's only so much we can practically do in a car, we stop. What happens when practicality isn't a problem? How far do we go to tame reflections in the listening environment (not the speaker measuring)? How much is too much (ie: anechoic)? How much is needed? 
Do we ever have the liberty to make this choice?

And while I'm at it, does it really matter if we gate measurements on speakers alone? I've never seen the applicability to doing this for any of our own purposes, given we are already in X environment. I see why mfg's do this, to give the consumer a useful reference point for comparison, but in the consumer's hands, does it really matter anymore?


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## ItalynStylion (May 3, 2008)

^That thought has crossed my mind more than once. I came to the conclusion that any car that is actually drivable wont reach that point. After I decided that....I went to bed lol


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## lycan (Dec 20, 2009)

bikinpunk said:


> which brings up something I've wondered from time to time: how much is too much?


 3/4


> A lot of the reason we car audio guys harp on reflections is because it detracts from a focused image. We do what we can to tame it, but given the fact that there's only so much we can practically do in a car, we stop. What happens when practicality isn't a problem?


 black holes 


> How far do we go to tame reflections in the listening environment (not the speaker measuring)?


 go too far, and you're outside the car


> How much is too much (ie: anechoic)?


 3/4 (already told ya)


> How much is needed?


 less is not enough


> Do we ever have the liberty to make this choice?


 you never have the liberty to always choose



> And while I'm at it, does it really matter if we gate measurements on speakers alone?


 not to me



> I've never seen the applicability to doing this for any of our own purposes, given we are already in X environment. I see why mfg's do this, to give the consumer a useful reference point for comparison, but in the consumer's hands, does it really matter anymore?


didn't matter a minute ago, maybe it does now


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## 14642 (May 19, 2008)

Gated measurements in a car are as useless as tits on a boar hog. This is the whole point. All of the reflections from adjacent boundaries (and they're almost all adjacent in a car) are heard as the speaker's reponse. They affect what we hear as the frequency response shape and the location of the speaker. Putting some foam around the speaker might help, but the help is so miniscule that it doesn't even make sense to spend any time or effort on it. 

If you wanna go nuts and completely re-upholster the inside of your car, add thick foam and fiberglass insulation in varying densities to eliminate as much of this as you can, Mark Eldridge-style. Go ahead--it'll sound kinda like a pair of headphones unless you replace the reflections you've eliminated with some new ones, but you'll need more speakers and some good DSP (room synthesis). My point and the point of the graphs I've posted is that it's sufficient to just EQ the car and add the additional reflections with the room synthesizer. Why go through all the unnecessary hassle or eliminating them since they're basically an EQ anyway?

Look at it this way. You can have a weed free yard or you can have a yard that appears to be weed free. I'm simply suggesting that if you set the mower a little lower, it won't be possible to distinguish weeds from grass.


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## ErinH (Feb 14, 2007)

Thanks, Jeff. Those were the exact answers I wanted. Well, only 3/4 of them. But that's good enough.


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## ErinH (Feb 14, 2007)

> And while I'm at it, does it really matter if we gate measurements on speakers alone? I've never seen the applicability to doing this for any of our own purposes, given we are already in X environment. I see why mfg's do this, to give the consumer a useful reference point for comparison, but in the consumer's hands, does it really matter anymore?



I should have clarified. I'm with you on car gating. 100%. I've done this and always wind up having more mess to 'clean up' with the data and realize halfway through, wtf am I doing this for. So, in a car I had already made up my mind. I was asking about the practicality of gating _at all_, car or not.


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## lycan (Dec 20, 2009)

Andy Wehmeyer said:


> Gated measurements in a car are as useless as tits on a boar hog. This is the whole point. All of the reflections from adjacent boundaries (and they're almost all adjacent in a car) are heard as the speaker's reponse. They affect what we hear as the frequency response shape and the location of the speaker. Putting some foam around the speaker might help, but the help is so miniscule that it doesn't even make sense to spend any time or effort on it.
> 
> If you wanna go nuts and completely re-upholster the inside of your car, add thick foam and fiberglass insulation in varying densities to eliminate as much of this as you can, Mark Eldridge-style. Go ahead--it'll sound kinda like a pair of headphones unless you replace the reflections you've eliminated with some new ones, but you'll need more speakers and some good DSP (room synthesis). My point and the point of the graphs I've posted is that it's sufficient to just EQ the car and add the additional reflections with the room synthesizer. Why go through all the unnecessary hassle or eliminating them since they're basically an EQ anyway?
> 
> Look at it this way. You can have a weed free yard or you can have a yard that appears to be weed free. I'm simply suggesting that if you set the mower a little lower, it won't be possible to distinguish weeds from grass.


ahh yes ... but will the tit-ed boar hog distinguish the weeds from the grass?

see what i'm sayn


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## lycan (Dec 20, 2009)

when Patrick returns to this thread of his, do you think he'll like what we've done (ok, what _i've_ done) with the place?


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## 14642 (May 19, 2008)

lycan said:


> when Patrick returns to this thread of his, do you think he'll like what we've done (ok, what _i've_ done) with the place?


 
He'll like what you've done better than what I've done. No one wants to hear, "don't bother with all of that hassle". From now on, I present Rube Goldberg-esque solutions.

OK. So to get rid of all of those reflections, you'll need to stitch together the foreskins of 1000 nordic wolves. Then, sew it up like a giant pillow and stuff it with long-fiber wool at a density of 11.7855632357 pounds per cubic inch (don't worry, the foreskins can take it). Then, remove all of the seats, the dashboard the carpet and the headliner. Spray 36 cans of silly string at the ceiling and before it dries, coat it with shellac. That will create a bunch of stalagtite-looking formations that will act as a diffuser. Then replace the seats with the giant foreskin pillow and get some of those seat belt extenders from Southwest Airlines to hold you in. 

Finally, call 1-800-MATTRESS and get a twin sized Sealey Posturepedic and staple it to the front of the car where the dashboard used to be. Shatter all of the glass with a cinder block and be sure to clean up all the shards. 

Now, you're ready for the intallation of the speakers.


or...just EQ the reflections.


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## tintbox (Oct 25, 2008)

Andy Wehmeyer said:


> He'll like what you've done better than what I've done. No one wants to hear, "don't bother with all of that hassle". From now on, I present Rube Goldberg-esque solutions.
> 
> OK. So to get rid of all of those reflections, you'll need to stitch together the foreskins of 1000 nordic wolves. Then, sew it up like a giant pillow and stuff it wit long-fiber wool at a density of 11.7855632357 pounds per cubic inch (don't worry, the foreskins can take it). Then, remove all of the seats, the dashboard the carpet and the headliner. Spray 36 cans of silly string at the ceiling and before it dries, coat it with shellac. That will create a bunch of stalagtite-looking formations that will act as a diffuser. Then replace the seats with the giant foreskin pillow and get some of those seat belt extenders from Southwest Airlines to hold you in.
> 
> ...


Very well put. Right on.


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## Patrick Bateman (Sep 11, 2006)

Andy Wehmeyer said:


> Gated measurements in a car are as useless as tits on a boar hog. This is the whole point. All of the reflections from adjacent boundaries (and they're almost all adjacent in a car) are heard as the speaker's reponse. They affect what we hear as the frequency response shape and the location of the speaker. Putting some foam around the speaker might help, but the help is so miniscule that it doesn't even make sense to spend any time or effort on it.


I agree that foam doesn't do a whole lot, but controlling directivity does. Psychoacoustically, it doesn't take a whole lot to mask those reflections; if you can reduce them by just 3-6dB, it changes the entire presentation. Heck, isn't this the reason that JBL uses waveguides? 



Andy Wehmeyer said:


> If you wanna go nuts and completely re-upholster the inside of your car, add thick foam and fiberglass insulation in varying densities to eliminate as much of this as you can, Mark Eldridge-style. Go ahead--it'll sound kinda like a pair of headphones unless you replace the reflections you've eliminated with some new ones, but you'll need more speakers and some good DSP (room synthesis). My point and the point of the graphs I've posted is that it's sufficient to just EQ the car and add the additional reflections with the room synthesizer. Why go through all the unnecessary hassle or eliminating them since they're basically an EQ anyway?
> 
> Look at it this way. You can have a weed free yard or you can have a yard that appears to be weed free. I'm simply suggesting that if you set the mower a little lower, it won't be possible to distinguish weeds from grass.


A few months back I was messing around with tweeter locations*, and realized that the most *accurate* presentation wasn't necessarily the most *enjoyable* presentation. For instance, I'd put on a very well recorded song, and the stage would actually exceed the width of the car. *But only if it was well recorded.* If I played a mono source, the stage was centered on the dash, the way I like it, with very little width.

That's basically what inspired this thread. I decided that I'd make a system that was "larger than life", _by design._ We're talking big fat wide imaging, intentionally blown out of proportion, just for the hell of it.

Your description of Mark's vehicle is interesting, because it reminds me of how my Unity horns sound. "Like a big pair of headphones." On a well recorded track, it's fun to "see into the mix", and hear all these little details that lesser speakers obscure. But the downside to this is a lack of ambience, since the waveguides do a fine job of eliminating reflections off the ceiling, floor, and windows. (Sure, they're still there, but there's a strong forward lobe and it doesn't sound *anything* like a conventional direct radiator.)


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## ErinH (Feb 14, 2007)

Geddes himself all but said said gated measurements are useless in the car. 



> The ear hears in very short intervals of about 10 ms so it really is capable of detecting the direct field seperate from the reverb field and this is a critical aspect of sound reproduction. Doesn't work in cars though.


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## lycan (Dec 20, 2009)

bikinpunk said:


> Geddes himself all but said said gated measurements are useless in the car.


That's a bad quote. The "car" is not some environment that magically defies the laws of acoustics & physics.

The car will obey any laws of acoustics & physics that apply to small, reflective environments. If the reflections are within the Haas limit (let's say less than 10msec, to be safe), then the ear will not distinguish those reflections from the original source. THIS principle works in a car, a home, a studio ... or any other environment.

Knowing this principle, we can therefore conclude that gating the speaker output in intervals less than 10msec doesn't have any merit, in small reflective environments. A car is a small, reflective environment ... therefore, gating doesn't make sense in the car.

You guyz know that I like to describe & analyze reflections with image sources. Place the image sources _outside_ the reflective surface(s), remove the reflective surface(s), and you've got an identical soundfield inside the reflective environment. Gating the speaker's output would be akin to ignoring the image sources. Our ears can't do it, if the image source output arrives within 10msec ... therefore, there's no reason for the measurement to do it either.

The laws of acoustics apply to _any_ environment. Of course, you have to comprehend the unique constraints _imposed_ by each environment, to apply the laws properly ... but the same fundamental laws apply to home, car, studio, or any environment you choose.


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## ErinH (Feb 14, 2007)

May be a bad quote, but I understood what he meant. In retrospect, maybe I should have clarified the context from which it was taken.
However, the bolded below is what our conversation was about, and was the basis for the above quoted.



lycan said:


> The car will obey any laws of acoustics & physics that apply to small, reflective environments. If the reflections are within the Haas limit (let's say less than 10msec, to be safe), then the ear will not distinguish those reflections from the original source. THIS principle works in a car, a home, a studio ... or any other environment.
> 
> *Knowing this principle, we can therefore conclude that gating the speaker output in intervals less than 10msec doesn't have any merit, in small reflective environments. A car is a small, reflective environment ... therefore, gating doesn't make sense in the car.
> *


FWIW, our conversation was prompted by the same thing I asked you about yesterday, Jeff.


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## lycan (Dec 20, 2009)

I just don't like phrases such as : "doesn't work in cars"

It leads some people to believe that cars are magical places, where physics & acoustics don't apply.

Better to say that "gating doesn't make sense if you've got reflections within the Haas limit". Then, you see if that _universal_ statement applies to the particular environment of interest.


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## Patrick Bateman (Sep 11, 2006)

lycan said:


> That's a bad quote. The "car" is not some environment that magically defies the laws of acoustics & physics.
> 
> The car will obey any laws of acoustics & physics that apply to small, reflective environments. If the reflections are within the Haas limit (let's say less than 10msec, to be safe), then the ear will not distinguish those reflections from the original source. THIS principle works in a car, a home, a studio ... or any other environment.


In this project I am going to intentionally add reflections to the mix, in order to create a soundstage that's larger than life. Any suggestions for what time interval I should use? Last night I modded one of my waveguides to do this, so that it's a dipole. Based on the front to back spacing, the delay is about one millisecond, give or take half a ms.

Here's a pic of the device.


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## SSSnake (Mar 8, 2007)

> or...just EQ the reflections.


Got it and I understand your reasoning BUT what happens when what you are trying to fix is a null. The EQ is not much help in this situation (I know, nulls are less offensive than peaks...).

In general I think the "EQ the reflections" gets you 90% there. What about the other 10%? I know that some cars sound better than others no matter how much EQ you pour into them. I'm not speaking about cars where one had an obviously deficient install either. These were what should have been comparable cars. So what was the difference, a better tune? Maybe, but several of these cars were tuned by the same guy. At that point is it just one car is better suited to sound reproduction?

My next question is why is elimination/reduction of early reflections impossible? At 100hz? Yep, I agree. What about 1,000? 2,000? 4000? I agree that eventually we are getting to the point of diminishing returns but Geddes typically sets 1000hz as the threshold for home drivers. So given the size constraints of a car what can we afford (space wise) to do?


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## lycan (Dec 20, 2009)

Patrick Bateman said:


> In this project I am going to intentionally add reflections to the mix, in order to create a soundstage that's larger than life. Any suggestions for what time interval I should use? Last night I modded one of my waveguides to do this, so that it's a dipole. Based on the front to back spacing, the delay is about one millisecond, give or take half a ms.
> 
> Here's a pic of the device.


Using reflections to create a "larger than life" soundstage is a dicey proposition. The naturally wide stage that basic stereo is capable of achieving does _not_ "depend" on reflections to achieve it; and, consequently, we often find in small, reflective environments that taking steps to _reduce_ reflections will actually _widen_ the stage.

However ... do keep us posted!


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## lycan (Dec 20, 2009)

cajunner said:


> I'm not understanding fully, it sounds like you and Andy are both in favor of equalizing the response warts (reflections) and all but isn't using waveguides doing the same thing in so much as reducing the reflected sound relative to the direct sound? Just in a physical (acoustic) and not electrical sense?
> 
> And if this is the case, then a system that uses equalization _and_ acoustic wave-guides would be even better than one without the other?
> 
> ...


It's not an "all or nothing" proposition, in my view.

Yes ... i think it makes sense to reduce or minimize reflections. In my understanding and experience, the reflections rarely "help". If you're clever, you might uncover something interesting by intentionally using reflections ... but they tend to cause more harm than benefit. Waveguides, "aiming" tweets to reduce reflections (and combat side bias), arguably fall into this category. Some techniques are more effective than others, of course.

However ... given that you can't eliminate reflections altogether, we have no choice but to EQ the remaining or "residual" ones ... that arrive quickly ... with the main radiator, since the ear can't distinguish.

As far as determining "how bad" the offensive ones are, YES ... later in time, and lower in amplitude tends to "limit" the reflections of concern. As I responded to Andy, we really _don't_ have a million tweeters to worry about ... i think the number is substantially less 

EDIT : as far as dash tweets go, you _always_ have the comb response to contend with. Again, it's not as simple as "present or absent". How large the reflection is (compared to the primary) and it's corresponding delay, will tell you the comb response : the position and depth of the null will depend on these two variables. Moving the tweet's position and aiming around up near the windshield will vary these two parameters, and therefore vary what the comb response looks like. It's always there, never simply "present or absent".

EDIT EDIT : some reflections are of course useful. Wall-loading or corner-loading a sub, for example ... more output, with a first comb null that will be well beyond the driver's passband.


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## ErinH (Feb 14, 2007)

I know you didn’t ask me, but since it’s up for discussion I figure I’ll throw my hat in as my own way of ‘thinking this through’…



SSSnake said:


> Got it and I understand your reasoning BUT what happens when what you are trying to fix is a null.


This is where knowledge of what causes the null comes in. Is it reflective cancellation? Is it a phase issue? 



SSSnake said:


> Geddes typically sets 1000hz as the threshold for home drivers.


Does he do this due to environment? The floor, the surrounding walls? That frequency has a wavelength of about 13 inches. Wonder why it’s that number? 



SSSnake said:


> So given the size constraints of a car what can we afford (space wise) to do?


My guess would be to take the nearest surface, and find the frequency at which the distance from driver to said surface equals the wavelength. Anything above this frequency would have a fully developed wavelength and would reflect. So, say you have pillar mounted tweeters, and out of everything in your car, the smallest distance you have between a driver and a surface is the tweeter to the dash. This distance (for example) is 2 inches. That = 7000hz. So, anything above 7000hz would be subject to reflections.
http://www.mcsquared.com/wavelength.htm

^ Just me talking through this out loud. I have no idea if that’s right or wrong. My problem is if I simply read something and don’t talk it through, I rarely remember what we talked about.


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## lycan (Dec 20, 2009)

bikinpunk said:


> I know you didn’t ask me, but since it’s up for discussion I figure I’ll throw my hat in as my own way of ‘thinking this through’…
> 
> 
> 
> ...


Listen to me ... throw this "fully developed wavelength" stuff away. Do it now. I don't know where it started, but it's hung around way too long.

Do this instead : analyze reflections with image sources. Put an image source where the image appears, and throw the reflective boundary away too.

Now, we can analyze reflections the EXACT same way we analyze two (or more) sources .. without _any_ reflections. Now, we see that cancellations from "reflections" and "phase issues" are the _exact same thing_ 

Inside the reflective environment, the soundfield that results from image theory is _identical_ to the one that exists with reflective surfaces. In other words, it's valid for _any_ wavelength and _any_ listener position. The concept of "fully developed wavelengths" will end up in the trash can of useless concepts, where it belongs.


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## ErinH (Feb 14, 2007)

I know where it came from. 

This bit still confuses me:


> Do this instead : analyze reflections with image sources. Put an image source where the image appears, and throw the reflective boundary away too.


Do you mean to physically move the speaker to where it appears to be coming from due to the reflections? 


I'll stay tuned for you to answer Charles' questions, because this stuff interests me.

Edit: Well, my 2nd guess would be correlation due to intensity of reflected material due to distance.


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## lycan (Dec 20, 2009)

bikinpunk said:


> I know where it came from.
> 
> This bit still confuses me:
> 
> ...


You've got a "primary" speaker, some distance *x* inside a reflective surface, and the reflective surface itself. And of course you've got the listener inside the reflective surface too 

How to analyze the resultant soundfield, due to primary plus reflection?

It's simple : put a _secondary_ speaker a distance of *x* _outside_ the reflective surface, so it's located *2x* from the primary. Now remove the reflective surface 

The soundfield inside the reflective surface will be the same, in both cases. Identical for all wavelengths (at least, for all frequencies where the primary tends to radiate uniformly in all directions, and for frequencies where the surface is a good reflector).

This is for analysis purposes only. You don't actually get out the piano wire and remove your windshield, and mount a secondary speaker on your hood 

Now, we can use the EXACT same tools to study reflections that we use to study arrays, off-axis response of drivers, etc ... namely, simple comb filtering math 

It's _all the same stuff_ ...

And its' the reason why we say that you're kidding yourself, if you think you're only aiming _two_ tweeters inside a car with windows ...


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## SSSnake (Mar 8, 2007)

> This is where knowledge of what causes the null comes in. Is it reflective cancellation? Is it a phase issue?


I'm not sure I understand your point here. It would be the result of reflections that are out of phase with the original waveform at the listening position. So, yes and yes.



> Does he do this due to environment? The floor, the surrounding walls? That frequency has a wavelength of about 13 inches. Wonder why it’s that number?


His design (if I remember correctly) uses a waveguide and a large direct radiator. The waveguide and the radiator have roughly the same polar response at the xover freq (he is using beaming of the woofer to his advantage). He mentions that going lower with directivity control would be preferrable but puts it in the column of too hard for too little benefit (again if I remember correctly).



> My guess would be to take the nearest surface, and find the frequency at which the distance from driver to said surface equals the wavelength.


Alright, this gives us some threshold to work with BUT are we assuming the directivity pattern is omnidirectional for this? And why one wavelength? Why not 1/4 wavelength?


I guess the big question for me is what can we glean from the Haas effect? Can we assume if that we must delay the reflections by greater than 10, 20, 30 ms for them not to be summed in the original response? Is there some formula relates between magnitude and delay?


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## lycan (Dec 20, 2009)

The _frequency_ at which the first comb null appears will depend on : the time delay between primary source and reflection (or between primary source and image).

The _depth_ of the first comb null will depend on : the magnitude of the reflection (or image) compared to the primary source. If the magnitudes are identical, the null will be infinitely deep (perfect cancellation). If the magnitude of the reflection is only half of the primary, the null will only be 6dB deep.

Never a really good idea to try to EQ nulls


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## Patrick Bateman (Sep 11, 2006)

lycan said:


> Using reflections to create a "larger than life" soundstage is a dicey proposition. The naturally wide stage that basic stereo is capable of achieving does _not_ "depend" on reflections to achieve it; and, consequently, we often find in small, reflective environments that taking steps to _reduce_ reflections will actually _widen_ the stage.
> 
> However ... do keep us posted!


As a general rule, I've found that dipoles create a jaw-dropping soundstage. A lot of people attribute this to the "boxless" design. IMHO, it's the radiation pattern. Reflections off the back wall create a pleasing sense of ambience. The interesting thing about dipoles is that our brains are able to perceive the original sound source. IE; you would think a dipole would sound "muddy", but they don't at all. Arguably, dipoles and horns are the "trendiest" thing in DIY home audio at the moment:

diy dipole - Google Search

If you go to the very first hit on Google, you'll get an interesting article from John K about U-Frame dipoles:

DIY-dipole-1

I really like dipoles, and the consistently positive reviews of speakers from Linkwitz, Nola, and Vanderstien seem to indicate that others do to.

Waaaaaay back in the day, over a decade ago, I noticed something odd. Under dash horns sounded pretty darn good before you sealed them up. At the time I had no idea why that was. I mean, who on earth runs HLCDs with a bare driver on one end? Of course, this was half a decade before John K wrote about U-Frames, and about the same time that Linkwitz was starting to document dipoles extensively.

On the left is the one I threw together last night:









Here's a rough design for the new one. It uses push-pull woofers to reduce 2nd harmonic distortion, along with an underhung motor and copper cap on the voice coil to extend high frequency response.


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## lycan (Dec 20, 2009)

Patrick Bateman said:


> As a general rule, I've found that dipoles create a jaw-dropping soundstage. A lot of people attribute this to the "boxless" design. IMHO, it's the radiation pattern. Reflections off the back wall create a pleasing sense of ambience. The interesting thing about dipoles is that our brains are able to perceive the original sound source. IE; you would think a dipole would sound "muddy", but they don't at all. Arguably, dipoles and horns are the "trendiest" thing in DIY home audio at the moment:



yep ... i understand dipole radiation, and the newest fad in audio 

HOWEVER ... the "ambience" that you (and others) love is indeed "ambience", by virtue of two things i think :

1. relatively healthy, flat power response ... or, an off-axis response that's a "faithful representation" of the on-axis response.

2. equally, if not more, important : ambient reflections that arrive _greater_ than about 10msec from the original. Put those lovely dipoles substantially _less_ than maybe 4~5 feet from the back wall, and what was once ambience is now ... well, mud.

The moral of the (same old) story is : reflections, or late arrivals (by using a _delayed_ difference signal for rear fill, for example) do indeed add "ambience" ... providing that they don't arrive too soon!


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## lycan (Dec 20, 2009)

cajunner said:


> thanks again, that's very helpful.
> 
> so if I'm getting this right, the distance between the radiator and the reflector dictates the frequency at which the null occurs, when it is within the passband (or harmonics) of the primary radiator.


no ... the distance between the radiator and it's image, which is twice the distance between the radiator and the reflecting surface, determines the frequency where the null occurs. Don't need to "remember" that ... just remember that the _time_ between first arrival & second arrival determines the frequency of the first null (it also determines every other null, and peak too!). Also, the null may be in the passband, and the null may not be in the passband ... it occurs, where it occurs. But if it's not in the passband, we don't have to worry about it.


> I was getting confused about "image drivers" but I think what you are saying is that the point of reflection where the sound is re-radiated off the surface becomes another sound source (and measurements would come from that point?) that is part of the total response based on the Haas distance, and in a car it's all Haas...


don't be confused .. this isn't even acoustics. Forget audio ... look at yourself in the mirror. That guy you see looking back is your "image". Move back from the mirror. In which direction does your image move? All i'm saying is this : instead of a face, there's a loudspeaker looking at it's reflection. Put a second loudspeaker WHERE THE IMAGE IS ... not on the surface, not at the exponential derivative of the Haas distance ... PUT A SECOND LOUDSPEAKER WHERE THE "VIRTUAL" IMAGE IS. Now, remove the reflective surface. Period  Soundfield is the same now ... with TWO sources, instead of one source plus reflecting surface.

Now, with that established, we can take a second step. If the arrival from our new second source (virtual, or image source) arrives within 10msec from the primary source, the mind will not distinguish the second arrival from the first. Instead, the two sounds (primary, plus secondary from virtual/image) will "conspire" to muck-up the frequency response, and probably localization as well  This is where the Haas limit comes in 


> if this is the case, then it's starting to sound like Bose 901's where they were to be placed in a specific listening environment for best results...
> 
> but another question... (sorry..:blush: ) is the distance from radiator to reflective surface just a matter of taking a measure and finding the corresponding wavelength at that distance to tell where the null will occur, or is it logarithmic and not simple math?
> 
> ...


it's simple math ... but there's no logarithms involved (until we convert amplitudes to decibels, anyway)


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## lycan (Dec 20, 2009)

cajunner said:


> OKAY! I feel like I just survived 7th grade Geometry with Mr. Davis...
> 
> 
> now I'm gonna guess that the smaller the "msec" figure is, the less muddy/mucked-up the sound will be?


not necessarily.

If the arrival from the second source is within 10msec or less, the secondary will be indistinguishable from the primary. How does this "confusion" show up? In FREQUENCY RESPONSE, it shows up as comb filtering. In LOCALIZATION, it will show up as a different "cone of confusion" (where ITD's rule). 

If the arrival is greater than, say 10msec and less than 20msec, you get "ambience". May be a good thing.

So ... less is not always better, it's not quite that simple.


> And this relates to the same comb filtering that happens when you have two mids in a door?


Yes, exact same thing  Two "manifestations" of the same effect : a signal plus a delayed, and possibly attenuated, version.


> And this is not really an EQ fix?


Right ... hard as hell to do. In geek-speak, delays are "zeros". Good compensation requires "poles". Poles present stability problems, chew up electronic dynamic range ... great cost, with little benefit. Bad choice.


> Would the BBE sound maximization circuit have any effect on this apparent muddiness? And is it possible to create the BBE correction using a time alignment processor.... wait, I'm getting ahead of myself..


OK ... stop the random, shotgun questions 



> so what happens when you use the windshield/dash junction as the top and bottom surface planes of a waveguide? Seems like this would be the easiest way to get some "on the hood" soundstaging.. No reflections, and two pure planes that wouldn't distort the wave where it hits your ears at maximum intensity first, and all reflections coming after the wave has passed your head and slammed into the back glass of the rear window.


can you SEE the reflection of the driver in the windshield? If you put an image driver where the reflection is ("behind" the glass, where all reflections are) ... and remove the glass ... do you think you can hear it?


> anyone been able to run a waveguide from the floor, behind the dash, and into the windshield/dash junction? Is this a stupid idea or what...
> 
> haha...


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## audiguy (Jul 30, 2007)

Andy Wehmeyer said:


> Gated measurements in a car are as useless as tits on a boar hog. This is the whole point. All of the reflections from adjacent boundaries (and they're almost all adjacent in a car) are heard as the speaker's reponse. They affect what we hear as the frequency response shape and the location of the speaker. Putting some foam around the speaker might help, but the help is so miniscule that it doesn't even make sense to spend any time or effort on it.
> 
> If you wanna go nuts and completely re-upholster the inside of your car, add thick foam and fiberglass insulation in varying densities to eliminate as much of this as you can, Mark Eldridge-style. Go ahead--it'll sound kinda like a pair of headphones unless you replace the reflections you've eliminated with some new ones, but you'll need more speakers and some good DSP (room synthesis). My point and the point of the graphs I've posted is that it's sufficient to just EQ the car and add the additional reflections with the room synthesizer. Why go through all the unnecessary hassle or eliminating them since they're basically an EQ anyway?
> 
> Look at it this way. You can have a weed free yard or you can have a yard that appears to be weed free. I'm simply suggesting that if you set the mower a little lower, it won't be possible to distinguish weeds from grass.



You absolutely do not want to lower the mower! If you lower the mower, you cut the grass so low that it doesn't provide any shade to kill the weeds. It is a deadly cycle. Now, back to our regularly scheduled programming...


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## Patrick Bateman (Sep 11, 2006)

I spent a few hours listening to the black dipole horns which I posted earlier. Here's some subjective impressions.

First off, the soundstage is waaaaaaay wider than my Unities. Admittedly, this is exaggerated, but I've acknowledged that this is by design. Even a mono podcast has a soundstage which exceeds the width of the car. Definition of the stage was surprisingly good. For instance, on most speakers the stage tends to crowd around the drivers side, and it's difficult to delineate any elements in the mix. On most speakers, the stage is basically an amorphous blob. On these dipoles, a bit of fiddling with the balance knob centered the stage over the dash, but elements of the mix were clearly defined beyond the confines of the center. In other words, the stage is wide *and* defined (at least on well recorded tracks.)

I had some concerns that the additional ambience would make the stage wider but at the expense of intelligibility. (Since the front and the back wave of the speaker is seperated by 7-20".) Oddly enough, the intelligibility is VERY good. Better than a direct radiator, and even rivals my Unities. One of my "torture" tracks is "Lazy Eye" by Silversun Pickups, because the lyrics are nearly unintelligible, even on the best systems. The black dipoles played it back with aplomb.

I'm at a bit of a loss with this one. I haven't studied speech intelligibility as much as I'd like. It seems to me that the dipoles should be audibly worse, but this doesn't appear to be the case. Here are some links for the curious:
intelligibility reverberation - Google Search

The intelligibility was particular noticeable on "Hurt" by Johnny Cash, which is another one of the tracks I use to audition speakers. Compared to the Unities the stage was noticeably deeper, albeit lower. (With the Unities, it's at eye level.) Keep in mind these auditions were tweeter-less, so that would help the dipoles.

Reducing listener fatigue is important to me, and the Unities still have an edge here. I had a LOT of problems with resonances in these fiberglass horns, and I can still heart a bit of faint buzzing. The dipole radiation improves the situation a great deal, because the overall efficiency is higher. (You might say that the signal to noise ratio is higher, since more sound is being radiated by the driver instead of the driver's enclosure.)

The real downsides to the black dipoles are twofold. First, they don't play very low. Even when they were sealed they were lucky to get down to 200hz in the car, and as a dipole, it's audibly leaner. The real achilles heel of the black dipole is the woofer itself. The specs of the woofer are very well suited for horn loading, but the motor is nothing special. You might call it "the Fostex sound"; due to the lack of shorting rings or an underhung motor, coupled to a very light paper cone, there's an audible distortion signature. It's not intolerable, but we can do better.

I hope this doesn't sound too negative; I actually like these horns a heck of a lot more as dipoles than as a conventional horn. But a modern motor would really take this to "the next level."


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## Patrick Bateman (Sep 11, 2006)

If anyone is playing along at home, here's a rough idea of how to build this thing. It's 18" wide, 9" deep, and 3" tall. All of the wood is leftover junk from the garage; ideally you'd want to use 1/4" baltic birch plywood. Note that the location of the woofer and the interior dividers are different than this diagram. Check out the pics to figure out the dimensions.























Here's a prediction of the response. Take this one with a grain of salt; hornresp tends to exaggerate peaks and dips in the measured response. I've documented this in the Triple8 thread. "In the real world", horns tend to measure flatter than the sims predict. On top of that, this horn is an unconventional one, which exacerbates things. Pay attention to the displacement - you'll need a highpass to keep from blowing this thing up.







Here's a pic of the horn with the top off. I haven't glued it together completely because I'm still tinkering with it.















By far the most difficult part of this build is mounting the woofers. These are two inch models from Peerless. One of the reasons that I didn't post much in March and April was that I nearly cut my thumb off the last time I worked with these things. Very small and delicate, and a p.i.t.a. to deal with. But they're one of a kind...







On a whim, I used PVC for part of the horn instead of plywood. I've found that it's possible to extend the high frequency response of a horn by avoiding right angles and sudden changes in direction. (For instance, a spiral horn is almost ideal.) Bill Fitzmaurice documented this nicely in Speaker Builder, and his web site. Anyways, the use of PVC in the horn is explicitly to extend the high frequency response. Note that the throat is just barely big enough to contain the woofers. Typically this flattens the response. If you do it too aggressively, it can hurt your power handling. So it's one of those things you have to tinker with.







Normally I listen to a pair of Gedlee Summas while I'm working, but I opted to listen to the new horns instead. Basically to get an idea of how they sound, without having to sit in the car.

I'm not going to go into a lengthly subjective description, but basically these horns sound much cleaner than the black ones. The Peerless woofers are audibly cleaner than the Misco. (And they should be; it's a more advanced motor.) Not too shabby for $8 each. Probably the most remarkable part of the presentation is how "big" it sounds. The bare driver sounds very small and tinny, but placed into the dipole horn, the woofers deliver real bass, and a presentation that belies their small size. Compared to the black horns, the new ones go lower *and* sound cleaner at the top.


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## highly (Jan 30, 2007)

OK, so once I have accepted Lycans' Corollaries of Reflection and agree that the brain can not distinguish between the real reflection and a reflection proxy driver under the circumstances previously described, and additionally that if the two individual sources arrive at the ears within the Haas interval of 10 ms unfavorable frequency domain issues will arise, how can we use this to our advantage? 

(I've depressed the "I Believe" button and wonder to myself 'Yeah, so?', albeit respectfully.)


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## ErinH (Feb 14, 2007)

Quick question: if the impact of intelligibility due to reflections is greatest at <10ms, then what if we _are_ able to come up with a way to delay the reflections so that they arrive >10ms after the initial image? Would that then allow us to get more ‘spaciousness’? 

2 things if the above is true:
1)	How do we do this? Attenuation is not the goal, as it would simply decrease the level at which we hear the delay. The goal would be to affect the delay time, not the delay level? Conversely, the effect of amplitude decrease is what gives us the spaciousness, no? 
2)	I suppose this is where the L-R method of rear fill to gain spaciousness comes in? The delay is due to the physical placement of drivers in the rear being further away than drivers up front.

Edit: 10ms=11ft. Nothing in the car is this distance away (unless you drive a limo ).


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## lycan (Dec 20, 2009)

bikinpunk said:


> Quick question: if the impact of intelligibility due to reflections is greatest at <10ms, then what if we _are_ able to come up with a way to delay the reflections so that they arrive >10ms after the initial image? Would that then allow us to get more ‘spaciousness’?
> 
> 2 things if the above is true:
> 1)	How do we do this? Attenuation is not the goal, as it would simply decrease the level at which we hear the delay. The goal would be to affect the delay time, not the delay level.
> 2)	I suppose this is where the L-R method of rear fill to gain spaciousness comes in? The delay is due to the physical placement of drivers in the rear being further away than drivers up front.


ten milliseconds corresponds to eleven feet. Those rear speakers are not far enough behind you, such that the arrival time from them would be 10msec _later_ than the fronts.

That's why "intelligent" use of rear-fill will :

1. Form the L-R difference signal
2. Bandlimit & attenuate the difference signal
3. DELAY the difference signal, on the order of about 20msec

If you do this right (skipping any of the steps is not recommended, if you want to achieve the desired effect), you will increase the sense of ambience in the vehicle, without detracting from the front stage (tonality, localization, or intelligibility). "Ambience enhancement" comes by virtue of : using the difference signal, _and_ adding additional delay in accordance with Haas.

Putting some drivers up by the windshield, a few inches from the glass, and expecting that reflective surface to "enhance ambience" just ain't gonna cut it, in my view  I'm not suggesting that this is what Patrick is offering, i'm just drawing a clear delineation: all possible types of "later arrivals" ... either by virtue of un-intended reflections, or intended processing ... are NOT created equal!


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## ErinH (Feb 14, 2007)

lycan said:


> ten milliseconds corresponds to eleven feet.


Yea, I realized this (and edited my post to say as much) after I typed all that stuff up. 


I say we all get together one day and talk in person. Everyone cool with meeting up in Decatur, Al? Cool. See you guys next week.


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## Patrick Bateman (Sep 11, 2006)

lycan said:


> Putting some drivers up by the windshield, a few inches from the glass, and expecting that reflective surface to "enhance ambience" just ain't gonna cut it, in my view  I'm not suggesting that this is what Patrick is offering, i'm just drawing a clear delineation: all possible types of "later arrivals" ... either by virtue of un-intended reflections, or intended processing ... are NOT created equal!


A lot of my previous projects were based on some solid theory, but this one is a bit different, since it was inspired by happenstance. I put two tweeters near the center of the dash, away from the windshield, and found that the width and depth exceeded their physical location by a great deal.

This was particularly amusing since it was such a simple solution. No complex waveguides, no three way Unity horns, no hideously complex passive crossovers.

If anyone wants to play along at home, the parts cost on this one is under $60. Parts Express doesn't stock those drivers anymore, but both PE and Madisound sell a model which is virtually identical, but with a black cone instead of silver.

The "dipole magic" is easy to mess around with. Just grab any ol' driver, suspend it away from the windows and dash, and listen... You'll likely hear an increase in spaciousness and a lot more depth.

The downside is a complete lack of bass.

Putting the speakers in a proper baffle would fix that, but we don't have the space. The horn in the pics above is basically a way to squeeze a relatively large baffle under the dash, while maintaining dipole radiation. So you get the "big" presentation of a dipole, in a form factor that fits under the dash.

One question that I have - Is the extra spaciousness due to reflected energy, the directivity of a dipole, or both? That's an important question, and only serious experimentation will provide an answer. One interesting observation is that the new horn "sounds" larger than the size of the enclosure. And even stranger, their apparent size seems to "bloom" as you move further away from them. For instance, if I listen to one of my Summas in mono, the apparent size of the image is a bit bigger than the enclosure itself. But that's a VERY big enclosure; it's over three feet tall. When I listen to this new horn in mono, it's size seems to dwarf the physical dimensions of the enclosure, particularly when I listen from a distance. Intriguing to say the least.

Anyways, would love to see some other people try this out. It's very simple to build. Be sure to use push-pull woofers, and a driver that has distortion reducing mechanisms in the motor. (Shorting rings, underhung, XBL etc...) You're also *very* limited on woofer size. Anything larger than a pair of small drivers is going to have HUGE peaks in the response, unless you have room for a VERY large enclosure under the dash.


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## onebadmonte (Sep 4, 2008)

Hi Patrick, I've got a few of those 2" peerless drivers. Could you post some plans on the horn you made? I'd like to give it a shot.


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## otis857 (Feb 12, 2008)

Great reading, as always!


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## ErinH (Feb 14, 2007)

a few subjective questions...


What recordings are we listening to? How do we know that the space we’re trying to attain is supposed to be there? Are we shooting for accuracy in playback (nearly infinite feat) or are we looking only to achieve something for ourselves with (potential) disregard for the way the material was recorded/meant to be played/produced/etc?


Thus, the cycle continues...


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## highly (Jan 30, 2007)

cajunner said:


> When somebody develops that little Class D 60 watt black box that delays and L-R difference signal in a 3X3X1 inch form factor, let me know...


Your wish may just come true!:laugh:

<threadjack>

I decided to shake the tree to see what happened, and was surprised to find I was hit on the head by what fell out. To whit:

I posted a 'can this be done with your product' thread on the MiniDSP forum and immediately garnered the interest of the developers. The thread is located *HERE*. 

The MiniDSP is a all-in-one DSP board that runs software plugin modules that define its functionality. It's endowed with two RCA inputs and four outputs and has separate modules for digital input and a digital 2x20 amplifier module. Configuration is over USB via a PC/Laptop, and it has an analog 'volume' control. Clearly a perfect match to the problem of intelligent rear fill. A MiniDSP board costs $99 US and each plugin is $10. You can only run one plugin 'chain' in a board at a time. Multiple boards can be run simultaneously but configuration is performed individually as in the Zapco products. Clearly this would be best leveraged as an intelligent rear-fill addon to an existing setup. The DSP runs happily in an automotive voltage environment. Due to the common ground, noise rejection may prove less than ideal in marginal systems, but I feel confident that we are all well enough aware of how to deal with noise, ground loops, and rejection strategies to make this a _relatively_ moot point.

Technical Specifications

- 24/56bit DSP Engine
- 24 bit ADC/DAC resolution
- 48/96/192kHz sampling rate configurable depending on plug-in
- Digital Audio input/outputs via I2S
- Nichicon Muse Audiophile capacitors
- Volume control by potentiometer
- Plug&Play USB driver and Software configurable for real time configuration by miniDSP plug-ins
- Device is not required to be connected to a PC once configured
- USB self powered device and wide range of DC power options (4.5 to 24VDC)

Anyone with even passing interest is highly encouraged to drop by, register, and add your encouragement. It appears they are actively interested in developing a plugin for this application and any encouragement we can provide can only help the cause. I attempted to spec the data flow clearly and with the highest probability for code reuse specifically to get the plugin generated. If there are significant departures from the flow we would be best served by agreeing upon those differences here and providing a single post modifying the requirement as opposed to everyone chiming in with a different requirement. Unified front and all.

I hope this generates enough interest to get the plugin built as it will open up a whole new world of options for an extremely attractive pricepoint.

</threadjack> 
Back to your regularly scheduled programming...

-Todd

Spinoff thread located HERE to prevent threadjacking and to encourage discussion.


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## dbiegel (Oct 15, 2006)

> no, really, this is nice, if the plug-in does it all and you can get the amp with the processor in a little box for 130 bucks, I'm sure a lot of people would give it a try in their systems to see if it's worth the investment.


Is there a way to "squeeze" these capabilities into one plugin so you don't have to buy extra $100 cards for each little thing? i.e. could they make one plugin that does basic EQ, time alignment, and intelligent rear fill? If you can do all that for $150, that would definitely be a huge seller.


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## highly (Jan 30, 2007)

dbiegel said:


> Is there a way to "squeeze" these capabilities into one plugin so you don't have to buy extra $100 cards for each little thing? i.e. could they make one plugin that does basic EQ, time alignment, and intelligent rear fill? If you can do all that for $150, that would definitely be a huge seller.


That's exactly the point. They are (considering) building a custom plugin for the sole purpose of fitting the entire processing chain into one DSP card. See the other referenced thread in my earlier post for details! Hop on the miniDSP.com forum, sign up, and chime in with a "Please?!" if you think it's an idea worth pursuing! These guys are looking at going out of their way to make this happen, but we HAVE to show support or it could well become vaporware!

-Todd


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## 75911 (Jan 27, 2010)

Patrick Bateman said:


> Anyways, would love to see some other people try this out. It's very simple to build. Be sure to use push-pull woofers, and a driver that has distortion reducing mechanisms in the motor. (Shorting rings, underhung, XBL etc...) You're also *very* limited on woofer size. Anything larger than a pair of small drivers is going to have HUGE peaks in the response, unless you have room for a VERY large enclosure under the dash.


why not a single 3" full range?


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## Patrick Bateman (Sep 11, 2006)

75911 said:


> why not a single 3" full range?


Basically the same reasons I like an array of drivers in lieu of one large woofer:


A 2" woofer can play to 6500hz before beaming is a problem, a 3" woofer starts to beam at 4000hz
When you use a pair of woofers, you can invert one to lower 2nd harmonic distortion
Comb filtering is a problem with arrays, but I can fix that by low-passing one of the two woofers

Basically an array offers the extension of the small woofer, with reduced distortion of a larger driver.


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## Patrick Bateman (Sep 11, 2006)

Patrick Bateman said:


> If anyone is playing along at home, here's a rough idea of how to build this thing. It's 18" wide, 9" deep, and 3" tall. All of the wood is leftover junk from the garage; ideally you'd want to use 1/4" baltic birch plywood. Note that the location of the woofer and the interior dividers are different than this diagram. Check out the pics to figure out the dimensions.
> 
> 
> 
> ...




I'm pretty happy with these horns(?) but I decided to rebuild them to implement three improvements.


I have the midranges wired in parallel to extract every last watt out of my amp, and the amplifier keeps shutting down. So I'm going to add another driver to change the load from 1.5ohms to 3ohms.
I've noticed that hornresp typically exaggerates the peaks and the dips in a horn. In the real world, reflections tend to smooth out the response. In this respect, horns behave differently than direct radiators, because direct radiators don't rely on resonances and reflections as much as a horn does. (The same holds true for transmission lines.) The addition of another driver will increase the "peakiness" of the horn, but I don't hear any obvious peaks, so I'm crossing my fingers that it will all work out.
Besides my amp shutting down constantly, my other complaint is that these don't play very low. You can see from the pics that the line is very short. Typically horns are tuned to one quarter wavelength at resonance. For instance, the compression driver in an Image Dynamics horn would likely resonate around 500hz. So the length of the horn is about seven inches. (13500 inches per second / 500 hz / 4)
I'm going to try something different, and tune my horn for one *half* wavelength. By doing this you lose some efficiency, but you lower excursion. And right now excursion is the limiting factor in this design, since there's no enclosure to contain the backwave of the driver. (In an Image Dynamics horn the backwave is absorbed by the plastic cup that covers the diaphragm of the compression driver.)

In a nutshell, I'm hoping that a longer line will give more bass, and the addition of a third woofer will increase thermal power handling and offset some of the efficiency lost due to the longer line.

Stay tuned...


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## DS-21 (Apr 16, 2005)

Why the Peerlesses instead of the Aura Whispers? The Whispers have ~2x the throw, and a considerably larger-diameter coil that can probably take more power.

Just an issue of what's on hand?


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## Patrick Bateman (Sep 11, 2006)

DS-21 said:


> Why the Peerlesses instead of the Aura Whispers? The Whispers have ~2x the throw, and a considerably larger-diameter coil that can probably take more power.
> 
> Just an issue of what's on hand?




One thing that I'm really nervous about is blowing a woofer. If you look at the horn design, it's all but impossible to remove a woofer once it's installed. I had some cone rubbing on one of the Peerless woofers, and I had to knock out one of the walls with a hammer to get it out of the horn! :O

So that was one of the reasons I wanted to bump up the thermal power handling. It should lower the possibility that I'll kill a driver.

As for the Aura Whispers, they're nice, but they're also the flimsiest woofer I've ever seen. I killed one just trying to solder a connection, and you can crack the frame by just looking at it sideways. Five years ago they were state-of-the-art, but I'd say the new offerings from Peerless and Vifa are superior.


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## DS-21 (Apr 16, 2005)

Hmm. I hated the old solder pad Whispers, but the newer ones have tabs that are much less annoying. They've been pretty reliable for me over the last six years or so, too.

Sound-wise, I've not yet made up my mind. The Whispers clearly do better lower and I kind of like their "tubey" midrange. The Peerless (at least the 830970's) have more extended and cleaner highs.


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## Patrick Bateman (Sep 11, 2006)

DS-21 said:


> Hmm. I hated the old solder pad Whispers, but the newer ones have tabs that are much less annoying. They've been pretty reliable for me over the last six years or so, too.
> 
> Sound-wise, I've not yet made up my mind. The Whispers clearly do better lower and I kind of like their "tubey" midrange. The Peerless (at least the 830970's) have more extended and cleaner highs.


I didn't even realize you could still buy the Whispers, and had no idea that you could get them with terminals. (If anyone's curious, Madisound has them.)

Isn't Aurasound out of business? I thought that's why PE was cloning their designs for the Neo Sym line. They're clearly a knockoff, just like PE knocked off the old Adire Audio woofers. (Unfortunately, they didn't bother to wait for Adire to close up shop!)

Anyways, I'll have to keep those Whispers in mind for future projects. They definitely have som advantages, in particular since they have a high FS, which is useful for a lot of horns.


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## Patrick Bateman (Sep 11, 2006)

On another forum, someone asked me to build them a set of Unity horns. Here's my reply, which may be interesting reading if you're considering a Unity horn in the car, or something like this:

_In a nutshell, all of my previous horns are in a pile in the corner of my garage. I have a habit of "going back to the well" to scavenge drivers for other projects, or even chopping up old horns. For instance, last year I built a Unity horn that I barely documented, that fits under the dash, and it used a horn that I built nearly a decade ago.

So I would be happy to sell some of my horns, if they weren't a gutted mess.

Having said that, I've documented my projects extensively. In fact I typically spend more time documenting them than I do *listening* to them! (I work at home, and will go two or three days without even using my car. Bicycles FTW.)

So if anyone wants to build a Unity, please do, I'd be happy to answer any questions about how it works.

Having said that, I've personally gone back to under-the-dash horns, at least for the moment, for a few reasons.

Here they are:

In a Unity horn, there's an upper limit to where the midranges will play. That upper limit is defined by the distance from the midranges to the apex of the horn. It's a real p.i.t.a., because it often creates a notch around 800-1200hz. Which is the last place you'd want a notch. There are two ways to fix this. The first is to use midranges with a very high EBP. The second is to use a bigger compression driver, that can play lower. Neither solution works well in the car. If you use a big compression driver, it's going to have to go under the dash.

The bottom line is this:









*If you want to approximate a point source, you need to get the drivers very VERY close together.*

The horns used by Richard Clark are one solution; he basically pushed an Altec to the extremes on a big horn, to squeeze as much bandwidth as possible out of them.









My Unity horns are from the same school of thought. Though the waveguide is smaller than Clark's horns, it uses the entire windshield to extend it. The windshield is a fundamental part of the design, and that's why I had to do all my measurements in-car.

Filling in the gap between the subwoofers and the waveguides on that project was maddening! There's no way to get two inch woofers down to 100hz on a shallow horn, and trying to find space for a proper midbass wasn't easy._
















Which brings us to this year's project.

I noticed that dipoles have a great sense of "space" and ambience, which is very nice in a car. At home we have the luxury of pulling our speakers away from the walls, which improves the imaging. In the car we don't have that luxury. While I know you can add that effect back in with a processor, I've always found a lot of processors to sound gimmicky and fatiguing. If you can get the same affect acoustically rather than electronically, that's the way to go IMHO.

Heaven knows I'm not the only one that likes dipoles; people have been going nuts for Linkwitz's designs for almost two decades.

But the original reason I pursued dipoles was simply to ratchet up the maximum SPL of a design. In my measurements I've found that a tapped horn offers an efficiency advantage of up to TWELVE db at some frequencies. (This was an apples-to-apples comparison using the exact same woofer, in a box that's size is comparable.)

I can post the data if anyone wants, it was a lot of measuring, and wasn't sure if anyone would be interested.

The bottom line is that we need to get the drivers VERY close together to approximate a point source, so close that the physical size of the diaphragm becomes a limiting factor. Dipole radiation bumps up our efficiency, and allows the use of a woofer that's smaller than what you would use in a sealed box. Last but not least, the dipole radiation adds a pleasant sense of ambiance and "air", which led to the name of this thread.

A two inch driver on a big shallow waveguide will never play to 100hz. But a pair of two inch drivers, along with a three inch to augment the last octave, CAN. The trick is to make it a dipole to get the efficiency where we need it, and to use a very long line - thirty eight inches in this case.


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## DS-21 (Apr 16, 2005)

Patrick Bateman said:


> Isn't Aurasound out of business? I thought that's why PE was cloning their designs for the Neo Sym line. They're clearly a knockoff, just like PE knocked off the old Adire Audio woofers. (Unfortunately, they didn't bother to wait for Adire to close up shop!)


I don't know if they're out of business or not. I know they fairly recently redesigned their website. But they definitely seem not to have supplied anyone.

I assumed that PE came out with their Aura knockoff stuff because some patent ran out. But then again, I also think if that were true then NRT motors would sprout up everywhere.


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## Patrick Bateman (Sep 11, 2006)

DS-21 said:


> I don't know if they're out of business or not. I know they fairly recently redesigned their website. But they definitely seem not to have supplied anyone.
> 
> I assumed that PE came out with their Aura knockoff stuff because some patent ran out. But then again, I also think if that were true then NRT motors would sprout up everywhere.


Did you ever notice that the designer of some of their woofers is named Ben Tang? I wonder if he ended up founding Tang Band. You can see his name on the spec sheets for the NS3 8E.


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## 75911 (Jan 27, 2010)

Patrick Bateman said:


> The bottom line is that we need to get the drivers VERY close together to approximate a point source, so close that the physical size of the diaphragm becomes a limiting factor. Dipole radiation bumps up our efficiency, and allows the use of a woofer that's smaller than what you would use in a sealed box. Last but not least, the dipole radiation adds a pleasant sense of ambiance and "air", which led to the name of this thread.
> 
> A two inch driver on a big shallow waveguide will never play to 100hz. But a pair of two inch drivers, along with a three inch to augment the last octave, CAN. The trick is to make it a dipole to get the efficiency where we need it, and to use a very long line - thirty eight inches in this case.
> 
> [/font]


have you listened to it yet?


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## bumpinP (May 5, 2010)

Patrick Bateman said:


> Which brings us to this year's project.
> 
> I noticed that dipoles have a great sense of "space" and ambience, which is very nice in a car. At home we have the luxury of pulling our speakers away from the walls, which improves the imaging. In the car we don't have that luxury. While I know you can add that effect back in with a processor, I've always found a lot of processors to sound gimmicky and fatiguing. If you can get the same affect acoustically rather than electronically, that's the way to go IMHO.
> 
> ...


I've been reading a lot of the Patrick Bateman posts and gotta say this is the project I find the most appealing - it seems to me like it's the one project that is complicated enough to be interesting and easy enough for almost anyone to recreate. Keep us posted on this one, please don't abandon this idea. Ideally what I would like to see is a total system plan using these as the centerpiece ..... similar to where you were going with the GNIB in a box thread. I know I'm getting greedy here, but it's only because I really enjoy your posts and the time you put into them. Thanks for all your hard work and dedication to the DIY community!


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## tyort1 (Jun 2, 2010)

What are your impressions now?


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## Patrick Bateman (Sep 11, 2006)

tyort1 said:


> What are your impressions now?


Still building it...

At these high frequencies you have to avoid sharp angles and you don't have the luxury of being sloppy when it comes to mounting the drivers. You might notice in the pics that everything is carefully recessed. That's not for cosmetics, it audibly improves the frequency response.

And all the wood that I'm using is kind of flimsy, which makes it hard to work with. (But it maximizes the volume of the enclosure, which further improves the response.)


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## Patrick Bateman (Sep 11, 2006)

On another forum, someone asked if "a tapped horn can play midbass." I've posted the answer here, since I'm in the habit of reading my own threads. (Sometimes I'll resurrect an old project even years down the road, and it's good to keep notes where I can find them. Which is right here!)

So, this is the answer to their question:

You might be interested in my new midbasses. They are not finished yet. Here are some "in progress" pics.
















In a nutshell, this is a Unity that's been turned inside out, but it's also a tapped horn. Sorta.

That's the simple explanation. Here's the complex one:

_






In a Unity horn, we've basically taken a conventional loudspeaker array and folded it into a horn. I've built a few unity horns, and there's a catch-22 in the design. To blend the midranges with the tweeter, you need to get them very VERY close together. The further apart they are, the lower the tweeter has to play. So you either need a REALLY robust tweeter, very small midranges, or both.















After building a bunch of small tapped horns, and measuring them, I started to realize that you can get some crazy bandwidth out of a TH. Much more bandwidth than the sims would predict. And then I started to figure out that there were some "tricks" to extend the bandwidth.

As it became apparent that a tapped horn can play higher than the sims would indicate, I became very interested in solving the catch-22 of the Unity horn.

In my new midbass solution, I've take the Unity and I've turned it inside out. Now the tweeters are on the outside, and the mouth goes *backwards*.

Tapped horns have limited bandwidth, but I've found that the use of multiple drivers smooths the response. I've also found that the high frequency extension improves as the woofer gets close to the outside of the box.

Which is why the tweeters in this design are all the way to the edge.

The 2nd driver is there to smooth the response, increase efficiency, and increase power handling.

The 3rd driver serves the same function as the midranges in a Unity horn; it's there to widen the bandwidth of the entire system. You might wonder why there is only one midrange, instead of four, and why it's only on one side. This is because it is also a tapped horn. In a tapped horn, the driver that plays the highest MUST be at the apex of the horn. If the tweeter was not at the apex of the horn you'd get a notch that would limit your high frequency response. (Due to this rule, the second tweeter in this horn is not playing full range. There's a low pass filter to prevent it from screwing up the response of the other tweeter.)

In the end, we have something similar to a Unity - an array that's loaded on a single horn. But flipped inside-out.
_

Here's the URL:
Space: The Final Frontier - Page 4 - DIYMA.com


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## Patrick Bateman (Sep 11, 2006)

If anyone cares, here's the midbass that I built last year, which gave me the idea that a tapped horn can play much higher than the sims would indicate. This enclosure is ugly, and the response is nothing to write home about. But there were a few things about it that showed promise:
























This is the frequency response. The purple line was measured outside, the red-line was measured in the car. It has a bandpass response of 125 to 250hz.

So what's the big deal?

The big deal is that the behavior outside of the passband is unexpectedly smooth, and the rolloff is gradual. The response is falling at a rate of 6dB/octave, and there are no peaks for a couple of octaves above the passband.

The package is also insanely small. Smaller than a vented box.

Basically, it got me wondering if you could get some of the efficiency of a tapped horn, along with the reduction in distortion, while widening the bandwidth.

So the new loudspeaker is a two-way array, but with something similar to tapped horn loading.


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## lostdaytomorrow (Jan 26, 2007)

Man, this thread is mind boggling. nice work.


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## Patrick Bateman (Sep 11, 2006)

The reason that I haven't put the last few walls in this horn is that I didn't know what would work. (Basically, how long should they be, how wide should they be, etc...)

So I made an Akabak model for the horn. Here it is. You can use this model for any tapped horn with three woofers. There are entries for two different woofer types. If I'm not mistaken, no one has published a tapped horn model which allows woofer types that aren't identical.

I believe you would get the best results by putting the bigger driver "deeper" in the line, and the smaller driver at the apex. By using two different drivers you spread out the impedance peak, and that improves power handling a bit, and smooths out the response, particularly in the bass.

System 'S1'

|================================================= ================================================== =====
|REQUIRED AKABAK SETTINGS:
|File > Preferences > Physical system constants:
|Sound velocity c = 344m/s
|Medium density rho = 1.205kg/m3
|Sum > Acoustic power:
|Frequency range = 10Hz to 20kHz
|Points = 533
|Input voltage = 31.62V rms
|Integration = 2Pi-sr
|Integration steps = 1 degree ... 1 degree
|Integration method = Cross
|================================================= ================================================== =====

Def_Const |Hornresp Input Parameter Values

{
|Length, area and volume values converted to metres, square metres and cubic metres:
Rg = 0.01e-0; |Amplifier output resistance (ohms)
S1 = 3.23e-4; |Horn segment 1 throat area (sq cm)
S2 = 9.70e-4; |Horn segment 1 mouth area and horn segment 2 throat area (sq cm)
S3 = 19.40e-4; |Horn segment 2 mouth area and horn segment 3 throat area (sq cm)
S4 = 25.02e-4; |Horn segment 3 mouth area and horn segment 4 throat area (sq cm)
S5 = 35.03e-4; |Horn segment 4 mouth area and horn segment 5 throat area (sq cm)
S6 = 45.54e-4; |Horn segment 5 mouth area and horn segment 6 throat area (sq cm)
S7 = 82.23e-4; |Horn segment 5 mouth area and horn segment 6 throat area (sq cm)
S8 = 116.00e-4; |Horn segment 5 mouth area and horn segment 6 throat area (sq cm)
S9 = 116.10e-4; |Horn segment 6 mouth area (sq cm)

L12 = 3.18e-2; |Horn segment 1 axial length (cm)
L23 = 6.36e-2; |Horn segment 2 axial length (cm)
L34 = 6.99e-2; |Horn segment 3 axial length (cm)
L45 = 30.62e-2; |Horn segment 4 axial length (cm)
L56 = 30.62e-2; |Horn segment 5 axial length (cm)
L67 = 6.06e-2; |Horn segment 6 axial length (cm)
L78 = 2.25e-2; |Horn segment 6 axial length (cm)
L89 = 0.63e-2; |Horn segment 6 axial length (cm)


|Parameter Conversions:

Sd = 54.00e-4; |Total diaphragm area for 2 parallel drivers (sq cm)

}

Def_Driver '830970'

Sd=13.00cm2
Bl=2.03Tm
Cms=8.30E-04m/N
Rms=0.27Ns/m
fs=170.0000Hz |Mmd = 73.86g not recognised by AkAbak, fs calculated and used instead
Le=0.01mH
Re=3.10ohm
ExpoLe=1

Def_Driver 'NS3'

Sd=28.00cm2
Bl=2.91Tm
Cms=1.10E-03m/N
Rms=0.20Ns/m
fs=140.0000Hz |Mmd = 73.86g not recognised by AkAbak, fs calculated and used instead
Le=0.30mH
Re=6.30ohm
ExpoLe=1


System 'System'

Resistor 'Amplifier Rg'
Node=1=2
R={Rg}

Driver Def='830970''Driver 11'
Node=2=0=9=15
Driver Def='830970''Driver 21'
Node=2=0=10=14
Driver Def='NS3''Driver 31'
Node=2=0=11=13

Waveguide 'Horn segment 1'
Node=8=9
STh={S1}
SMo={S2}
Len={L12}
Conical

Waveguide 'Horn segment 2'
Node=9=10
STh={S2}
SMo={S3}
Len={L23}
Conical

Waveguide 'Horn segment 3'
Node=10=11
STh={S3}
SMo={S4}
Len={L34}
Conical

Waveguide 'Horn segment 4'
Node=11=12
STh={S4}
SMo={S5}
Len={L45}
Conical

Waveguide 'Horn segment 5'
Node=12=13
STh={S5}
SMo={S6}
Len={L56}
Conical

Waveguide 'Horn segment 6'
Node=13=14
STh={S6}
SMo={S7}
Len={L67}
Conical

Waveguide 'Horn segment 7'
Node=14=15
STh={S7}
SMo={S8}
Len={L78}
Conical

Waveguide 'Horn segment 8'
Node=15=16
STh={S8}
SMo={S9}
Len={L89}
Conical

Radiator 'Horn mouth'
Node=16
SD={S9}


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## Patrick Bateman (Sep 11, 2006)

Another pic of the device.















This is the predicted response and the excursion with 20V. (100 watts into 4ohms.)
Based on the other tapped horns I've built, I'm expecting that the "real" response above 400hz will not be as peaky as this predicts. Usually it's the midpoint between the peaks. Which means that I should be able to get to 5khz with some response shaping in the crossover.

Or at least that's the goal


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## honfatboy (Jul 4, 2005)

Really enjoy this thread. Any new updates? Thanks!


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## Patrick Bateman (Sep 11, 2006)

honfatboy said:


> Really enjoy this thread. Any new updates? Thanks!


I bought a box of the Faital 3" woofers to take this project 'to the next level.'

But lost a lot of interested in car audio after buying a 4G air card for my laptop. Seems like I take the train as much as I use my car nowadays, because you can work on the train!

(It's kind of hard to work on the computer when you're driving lol)

I've had to jump start my car twice this month to start it, that's how little I drive now


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## loddie (Jun 23, 2006)

What's your impression on the Faital 3s? On diyaudio, you mentioned you had bought them and would provide feedback.


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## Patrick Bateman (Sep 11, 2006)

loddie said:


> What's your impression on the Faital 3s? On diyaudio, you mentioned you had bought them and would provide feedback.


Ummm they look good?

I wish I had some data to post about them, but they're just sitting there on a shelf. My interest in car audio has really plummeted lately I'm afraid.

The build quality on them IS very nice


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## vactor (Oct 27, 2005)

dang. PB's threads like this used to be stickied. where are they now?


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## Patrick Bateman (Sep 11, 2006)

vactor said:


> dang. PB's threads like this used to be stickied. where are they now?


I barely drive two days a week lately... And I don't need home speakers since I bought a pair of Summas.

I think someone else will have to take the torch...


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## 75911 (Jan 27, 2010)

do you live in Washington State or New York?


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## Patrick Bateman (Sep 11, 2006)

75911 said:


> do you live in Washington State or New York?


The NYC thing is a goof. I'm all over the west coast, mostly Oregon. 75% of the time I'm in the Portland area.


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