A-periodic Mat Questions

kfr01 wrote: Alright SQ fans, I have a couple questions. I like my enclosures small and my Q low. ;-) I don't care about SPL, so efficiency hits don't bother me. That said, door resonance drives me bonkers and my couple layers of raammat doesn't seem to catch them all. Since I'm going to be modifying my door for an Extremis midbass I've been thinking about trying an AP mat / mdf / fiberglass enclosure in the door rather than going straight IB. It seems to me that I'll obtain the sound I like and reduce IB-related door resonance at the same time with this strategy. Right? Wrong? Stupid? Any tips? Also, it seems that USDaudio is one of the only vendors of these products. Are the materials anything special? They look like some sort of regular insulation. Tuning? A few sites mention the need to experiment to correctly tune? Truth? Smoke? As long as I'm at it, will this strategy also work for kick panels? An AP vent out the back keeping the Q down in too-small kicks?

Wow... ummm, that's a lot of stuff. The wavelengths you will be dealing with from a mid-bass driver will be so long, that I don't think you are going to really gain anything at all in reference to a REAL aperiodic damping scheme. There may be some effect gained at the highest reproduced frequencies, but, seeing as the Extremis is about a 6.5 inch driver, the highest frequency you will want to take it to will be around 2000Hz. If I am not mistaken, this will be your 60 degree off-axis frequency. While the driver WILL reproduce frequencies above this, (and the Extremis will do it VERY WELL - ON AXIS) physics will still mandate a beaming effect at the wavelength equal to the diameter of the raditaing surface. ON AXIS, the response will go quite a bit higher. You will probably want to go with a three way system in the doors, which is what I am going to do. My Extremis will run 50 to 500, a three inch Vifa mid will run 500 to 3500 or 4000, and the Infinity eMIT ribbon tweeter will be running from that frequency and up. Ribbon tweeters represent FURTHER issues... their horizontal dispersion is FABULOUS, while vertically, they begin to beam much at a much lower frequency than horizontally. (The way around this is to simply tip the tweeter toward the front of the car, to about a 45 degree angle, and this will fix MANY of those anomolies.) The sound power in my car right now is HORRENDOUS, so I am hoping to fix all of these things with a three way system in the doors. Anyway, to answer a few of your questions in short simple answers - 1: The actual enclosure route is a great way to go, if a tremendous amount of work. 2: Try a layer of Black Hole 5 (EXCELLENT product, by the way) on a major portion of the outside door skin, in lieu of an actual enclosure and/or raammat. Easier to do than the enclosure route... Links: Here and Here 3: With the effort required, you should get a good return in sound quality. You will have to decide if the effort is/was worth it. 4: The USD product seems to be nothing more than a Variovent - a product you can (could?) buy from Dynaudio, (Link to Yahoo search) if you can find a dealer. Yes, they CANNOT be a fix-all for every issue, and if I remember correctly, they are only "lossy" down low. They would do you little to no good in a mid-bass setup, especially with a high-order highpass crossover. And yes, there will likely be tuning involved. Some truth, some smoke. I hope I didn't confuse the issues for you... This is just the way I see it.It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

Yes, I will be running the Extremis as only the midbass in a 3-way system. I am planning to play with the crossover anywhere from 250-700. Midrange & highs will be handled by my quart set in the kicks. I hope to get the extremis down to 63hz on a 24db cross. Follow up question to the first part, because I'm slow and haven't done my research: what effect does the wavelength have on a usd-type AP enclosure as opposed to an IB enclosure? Does anyone have any good resources on AP? Check here: http://usdaudio.com/products/ap.php and here: http://usdaudio.com/tutorials/ap-tut1.php it both looks easy and beneficial, without any real negatives. What am I missing? What are the negatives? Do I have anything to gain from this. I just noticed that Seas also sells a smaller AP product at madisound.com New Project: 2003 Pathfinder

Doing some searching. Gosh, not much decent out there about the AP mat concept. http://www.teamrocs.com/technical/pages/apmats.htm one link I was able to find... From that link: "In essence, you have a very large enclosure, the trunk, with a resistive element that controls and damps the energy transfer." That sounds pretty good to me if I replace the wood "trunk" with "door." :-) Another: http://www.electronixwarehouse.com/education/glossary/A.htm "Aperiodic Refers to a type of bass-cabinet loading. An aperiodic enclosure type usually features a very restrictive, (damped), port. The purpose of this restrictive port is not to extend bass response, but to yeild a smoother response pattern by lowering the Q of the system and reducing the impedance peak at resonance. Most restrictive ports are damped with quantities of sound absorbtive material." Then I compare the advantages / disadvantages of the IB alignment to the AP. http://www.mobileaudio.com/rac-faq/rac-faq_4.html The disadvantages of IB being: "1 Requires that a good seal be obtained between front and rear of driver. In a car, this can be quite difficult and may require the installer to remove trim panels to plug any holes that would let energy "bleed through". "2 The responsibility for damping cone motion rests solely on the driver's suspension. As fatigue sets in, this becomes a critical issue in infinite baffle set-ups." It SEEMS that AP would both reduce the bleed and help control the driver's suspension. This one is a bit juicier, but still lacking big time: http://www.maximacar.com/aperiodic.htm At least the characteristics of the Extremis seem to fit: low fs, low qts, high xmax. Getting warmer: http://www.elitecaraudio.com/article.php?sid=18 Wow. Yes. I'm not sure how accurate that guy was, but he at least gave a DIY way to accomplish this. I think the AP door concept sounds like a worthwhile experiment. I still haven't seen any negatives other than: (1) efficiency and (2) sealed is better. Since it is highly unlikely I'll ever get the right sized sealed enclosure in my door this AP concept might be the winner. Feedback? Haemphyst, my midbass minded friend? What say you? If nothing else I have a few nice links gathered in one place so others looking can get some AP info. :-)New Project: 2003 Pathfinder

I'm thinkin', *I'M THINKIN'*... LOL Gimme a minute.It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

kfr01 wrote: Doing some searching. Gosh, not much decent out there about the AP mat concept. http://www.teamrocs.com/technical/pages/apmats.htm one link I was able to find... From that link: "In essence, you have a very large enclosure, the trunk, with a resistive element that controls and damps the energy transfer." That sounds pretty good to me if I replace the wood "trunk" with "door." :-)

I can't say I disagree - there ISN'T much, is there? But in my experience (which I will admit is minimal in this arena) aperiodic damping is best left to lower frequencies. The aperiodic damping characteristics of a Variovent, or the like, is restrictive at the higer frequencies of the vent's passband, gradually "loosening up" as the frequency goes down - it gets more lossy the lower the frequency it is reproducing - thus allowing more air movement through the vent at the place it is needed most - the lows... I think you COULD use it in a mid-bass situation, but I have a sneaking suspicion you will have trouble finding something "off-the-shelf" that will be lossy enough at a high enough frequency to do you any real good. This is where the tuning I referred to in my previous post will become mandatory.

kfr01 wrote: Another: http://www.electronixwarehouse.com/education/glossary/A.htm "Aperiodic refers to a type of bass-cabinet loading. An aperiodic enclosure type usually features a very restrictive, (damped), port. The purpose of this restrictive port is not to extend bass response, but to yeild a smoother response pattern by lowering the Q of the system and reducing the impedance peak at resonance. Most restrictive ports are damped with quantities of sound absorbtive material."

OK, and what is this guy telling me that you and I don't already know. Thinking about it, I cannot see WHY everybody says "make the box this tiny..." Why? Wouldn't the better way to go be like this: Aim for a given Qts in your sealed system, test the enclosure, locate resonant peak, tune aperiodic damping plug for said peak, install. This is the way I think I would do it. The bother of having to build a perfect IB (impossible, as you know), enclose a very small volume on the back of it, install big, lossy vent, sacrifice efficiency, play music... too much effort for me. I know, you are asking for you, and I do firmly believe that you will probably end up with really good results, eventually. Will it be worth the effort for you? By the time you spend all of the money on parts (glass, wood, what have you) and you consider the value of your time, why not get a good, digital, true parametric EQ, and fix the issues you are having?

kfr01 wrote: Then I compare the advantages / disadvantages of the IB alignment to the AP. http://www.mobileaudio.com/rac-faq/rac-faq_4.html The disadvantages of IB being: "1 Requires that a good seal be obtained between front and rear of driver. In a car, this can be quite difficult and may require the installer to remove trim panels to plug any holes that would let energy "bleed through". "2 The responsibility for damping cone motion rests solely on the driver's suspension. As fatigue sets in, this becomes a critical issue in infinite baffle set-ups." It SEEMS that AP would both reduce the bleed and help control the driver's suspension. This one is a bit juicier, but still lacking big time: http://www.maximacar.com/aperiodic.htm At least the characteristics of the Extremis seem to fit: low fs, low qts, high xmax.

Read this one again - http://www.mobileaudio.com/rac-faq/rac-faq_4.html#SEC85 You missed the part about being a BIG driver. The Extremis is not... Here are two lines quoted from this same article: 1) You should probably only get an aperiodic membrane if you've got money to burn, lots of amplifier power, some big subs, a sedan, a desire for trunk space, and no wish to boom. If your tastes lean towards bass-heavy booming, as opposed to well-recorded acoustic instruments, you're not going to be pleased with the result. and number 2) An aperiodic membrane is one part of a type of subwoofer enclosure. It is an air-permeable sheet which has frequency-dependent acoustical resistance properties. The original design goes back to Naim, for use in home systems, but has been applied by several individuals and companies in car audio. All of this really confirms my feelings about keeping the mid-bass restricted to the vanilla flavored "IB" of the door... I know this is not what you wanted to hear, but I guess I am a defeatist...

kfr01 wrote: Getting warmer: http://www.elitecaraudio.com/article.php?sid=18 Wow. Yes. I'm not sure how accurate that guy was, but he at least gave a DIY way to accomplish this. I think the AP door concept sounds like a worthwhile experiment. I still haven't seen any negatives other than: (1) efficiency and (2) sealed is better. Since it is highly unlikely I'll ever get the right sized sealed enclosure in my door this AP concept might be the winner. Feedback? Haemphyst, my midbass minded friend? What say you? If nothing else I have a few nice links gathered in one place so others looking can get some AP info. :-)

Fiberglass insulation does NOT work... this much I remember from my tinkering of years ago. (This is about all I remember) I think we discovered that it was not stable enough thermally speaking. There were many anomalies discovered. I will see if I can locate some of my notes, and get them to you. We tried many different thicknesses of glass, various packing densities, and other adjusted parameters, and we were never really able to get good results. This might be why we simply dropped the experiments then. Discouraging, I guess it was. There's that famous defeatist attitude again. LOL There is a BUNCH of contradicting information out there. The one thing I do get from everything I was able to find, is that they sound really good... If you can make it work, by all means, go for it, and let everybody know how it all comes out... (BTW, I filtered some of your line spacing only to minimize the space occupied by my response.) Some interesting info I came across while studying for this thread... http://search.yahoo.com/search?p=aperiodic+damping&ei=UTF-8&fr=FP-tab-web-t&fl=0&x=wrt http://www.northcreekmusic.com/MAPD1.htmIt all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

haemphyst wrote: Will it be worth the effort for you? By the time you spend all of the money on parts (glass, wood, what have you) and you consider the value of your time, why not get a good, digital, true parametric EQ, and fix the issues you are having?

Thank you much for the feedback.  I probably will buy a good true parametric eq.  I will also probably try this AP mat thing.  I will not use the fiberglass.  ;-)

The time/money thing;  If I just wanted the end result I would have taken the car to an installer a long time ago.  This audio hobby of mine is how I decompress and I really enjoy it.  If some time/money spent on car audio keeps me sane when my weeks are rather long and tiring, it is well worth it.  Also, since the wife and I will be at different firms in different cities this summer, I'll have my evenings to either  a) pine over her   or  b) occupy myself with tweaking.  I'll probably do some of both.  Then the 4.5h drive to her and back every weekend will give me plenty of time for listening and evaluating.  :-)

New Project: 2003 Pathfinder

I can truly appreciate the sentiment... I wish I sometimes had time to decompress on MY OWN SYSTEM... LOL. Seems I am always working on somebody's computer or stereo, or doing some long distance tech support gig... sigh... God bless ya, and I hope all works out well. Keep me/us posted! I've said it before, but one more time can't hurt, I guess (if I start to sound like uthinkuknowho, stop me) but the Alto is really good stuff, if a bit pricey. I have a pair (yes, TWO of them) of the UCSPros, sadly still waiting for installation in the CAR system they were bought for. They are right now in my home system for eval purposes. Again, sigh...It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

I bounced this same question off my Harman engineer friend, and he is of the impression that the Q of the Extremis (and the Tang-Band, for that matter) is too low... the transient response, efficiency, and low-end frequency response will suffer TERRIBLY, he thinks, and I asked "Well how transient do you really think 350Hz can be?" and "Won't the door/floor boundary give you a little bit of gain down lower?" He thought those were good questions, as well, and after a few moments of thought, he agreed, that as a MID-BASS ONLY application, (50 to 350 or 400Hz) with a good 3 inch mid-range driver matched to it, and a good steep crossover slope (at least 24dB), he thinks the idea has merit... When you get started, let me know... I may follow your lead!It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."