I originally had huge plans for the audio system I was going to put in my A4...but after picking it up from the dealer I kinda thought to myself what a beautiful car, "I'd hate to hack it into a million pieces". <p>So I started to look around for aftermarket audio solutions and found one from JL Audio. Now I've never been a huge fan of JL...as I'm a student engineer at a competing company (Harman, aka Infinty, JBL..you get the picture)Anyhow this box the offer up looks like a pretty decent bet..I wonder if any of you have any first hand experiance with this system or possibly own one. I'm still going to do some cool stuff to the system...like for instance I'm going to derive the transfer function of the cabin (Low Frequency only as the HF is littered with all sorts of High Q comb filter like anomolies) and then I'll design an EQ circuit to work in concert with the JL product..that is if it's a decent system.<p>Anyhow I'm just curious if anyone is interested in such an idea...I'm pretty open to offering up any circuitry I design to the rest of the group..seeing as how everyone exchanges information so freely around here. Though I warn such EQ would be for only one Transducer / Enclosure combination...therefore by no means universal...in addition to this it would be optimized for only one combination of open / shut windows or sunroof...here one can see you should obviously optimze for all windows shut. As I've noted to the guys at JL...it would be really cool to do this stuff in DSP and have the EQ load up different coefficients for various combinations of windows open or closed or half way up ect...though you would have to be able to sense the position of the window in a fairly precise manner.<ul><li><a href="http://www.jlaudio.com/stealthbox/audia4.html">JL Audio StealthBox for Audi A4</a></li></ul>

I've got it. <p>I'd compare it to the response of a single sealed twelve. I was initially concerned that the infinite baffle design would be a bit boomy, but it really is pretty tight & controlled.<p>I originally crossed it over pretty high, but have since rethought it & it's currently crossed over at around 75-80Hz (still fairly high...but up front I'm using 5 1/4's).<p>Search the archives for stealth box & you should find tons of messages from people with it, including several great pictures.<p>The ease of install, custom fit, and OEM looks make it a total winner...the great sound is just icing...<p>steve

Steve,<p>There is no reason a properly designed infinite baffle system should sound boomy. If you've encountered boomy bass from IB designs it's probably because the box was too small thus evoking a relatively high Q at the Fc of the system...i.e. a big mutha of a peak. I can say this also..a vented system is not necessary in an automobile like the A4 as one of the primary reasons to pursue a vented it to extend the F3 (half power point) of the system to some lower frequency than would be attainable in the same box dimensions. The last thing you need in a car is a low cutoff as the cabin has a ton of gain usually it's approx a 2nd order rise starting at 50-60 Hz and going up from there as you approach DC. Well vented systems intrinsically feature a 4th order rolloff as opposed the the 2nd order rolloff of the infinite baffle system. If you were to design your system such that the F3 of your box was determined to match the start of the cabin gain you could have a nearly perfectly flat amplitude response...at least small signal (the roof might flex at it's first bending mode and to some extent cancel the output of the sub) this sort of response could not be so easily had because the steeper 4th order rolloff is not a good match for the cabin gain.<p>Anyhow thanks for the info...I'll look into it. BTW - I'm not a total nerd...this is actually what I do for a living while I get through college (student engineer)..I work for Harman International (infinity, JBL...ect ect)

i've read alot about speaker design & such (chem.eng myself). The boomy infinite baffle speakers I heard were mounted on custom panels behind rear seats in a large sedan (firing through seats). <p>All I can say however is that finding the transfer function of a four door car is going to be a "fun" project...I assume you have a tone generator & a very sensitive SPL meter from your workplace...I'd go for as small a delta as possible (cool if there is a computer program to do the work of changing freq & measuring SPL!...I'm jealous if ya got that...)<p>You're right tho'...as SPL increases, you get funny things that happen that ARE not linear. Question: say at 35Hz on a 0dB level played at 50% volume, you get a +2.1dB increase. Now if you play the same tone at 75% volume you get a +2.5dB increase. Does this type of thing happen? If so, you have a multidimensional transfer function based on input level & frequency that would make an EQ circuit have to take into account input level (not normally done, i don't think). <p>My last vehicle was a fullsize Bronco. It had an amazing transfer function...a single sealed 12 in a wedge firing rearward was so musical as to be practically transparent. I am not a bass-fanatic, but I wanted the bottom end to be fully represented...i got more than I could've hoped for. You could easily play painfully loud with 100W (+100W going up front) from a little PPI amp.<p>Anyway...in playing around, I noticed that the A4 is extremely sensitive to direction of woofer (I put the sealed 12 in the trunk to get a feel for it). Aiming it in different directions made for some nice sounds (and some very ugly ones...try firing sideways, angled slightly rearward...i think my trunk was planned on self-dehinging).<p>Lucky you work for a place that gives you lots of parts & tools to work with! I can tell you will have a variety of transfer functions dependant on placement & firing direction. Pick one & design for it & don't change. That car is so much more sensitive than a large open space like my Bronco.<p>An audio shop recommended a single 10 infinite baffle in the rear deck....but, I found the stealthbox & was sold. (BTW, I have had awesome luck with JLAudio)<p>Good luck & let us know! I have a PPI PAR-225 quasiparametric half DIN EQ in the dash...so if you find a transfer function, I would love to try to test it out with my EQ (I believe on the sub freq's I am centered at 45HZ with a pretty low Q...more for total bass boost control than for tweaking cabin response).<p>steve

Just curious, how much did you pay for the stealthbox? Where did you get it? I just got myself an 1.8Tqm on Saturday and am already missing the sound system that I tore out of my last car. Debating whether to build a new box for the JL 12W6 (currently in a odd shaped custom box made for my previous car) or get the Stealthbox.

I live in Houston too and saw a silver A4 getting a stealthbox installed about 1-1/2 weeks ago at Houston Car Stereo on 59. Very nice set up!

bad...bad...bad....bad<p>I was at !Custom Car Stereo! on 59 about a week & a half ago to get the Clifford Concept 60 alarm put in. Don't tell them that you thought they were Houston Car Stereo...totally different league....CCS is MUCH more professional than HCS.<p>I put the stealthbox (and the rest of the stereo)in myself about 4 months ago. If you search the archives, you can find all my work in doing the head unit, EQ in the ashtray location, front door speaks & stealthbox. Amp is temporarily on the back of the rear seat (no time for a neat job yet).<p>But, yeah it was probably my silver A4 you saw! <p>With the exception of accidently unplugging the headlight switch (fixed a couple days later in about an hour), custom car stereo did a great job! Would highly recommend them.<p>steve

by the way, they wanted something like $800 for the stealthbox! $579 is much, much more reasonable.