After some thought, I think you would be happiest with carpeting the whole thing. The carpet will tend to dampen the box reasonance. Shoot with that box I would just carpet every surface of the interior. I did this with a D-50 (Dodge) pickup I had several years ago. I built a box, hooked up a signal generator to find any imperfections, and sealed them. Then I carpeted the box and any exposed metal or surfaces which might tend to vibrate. It sounded pretty good. I had 150 watt 12" subwoofer that played through the seat. 70 watt midrange door mounts, and 30 watt tweeter surface mounts. It sounded good with NO tinny resonance sounds. Two songs I use to test this are Back in the high life, Steve Winwood- Has good high and lows and strong bass in spots. The other is shoot to thrill, AC/DC the bass drum solo in the middle will shake everything that might be loose so you can find it and tie it down.
My electrical engineer friend who helped me with my pickup said "remember, loud is not good unless it is clean".
I"m not one for big stereos... I tried to get involved with that several years ago but really lost interest. I am impressed by someone that has a good, clean, loud system. I am sick and tired of driving around and hearing these shoddy put together systems. Nothing bugs me more than to pull up next to a 12 year old Honda and the bass is all you can hear.... followed by the rattling of all the interior components. Worse yet, when their license plate rattles...I hate that.
Theres not much interior left. Except the doors. I can hear some imperfections in the mids and highs. But I need more control. Audio control. Thats a little down the road. Rigth now every piece of interior in that car has dynamat. That car is so quiet, a couple of days ago I was downtown with the stereo disconnected and windows up and a firetruck came about 20 meters from me before I heard it.
I know how irratating it is not to have good mids and highs. I guess that's why I'm running a 4 channel 800 watt Orion amp to 3 way componet sets. Plenty of overhead. Every thing I play on the stereo sounds so good, just a little more control would be nice. Especially up front.
The box does stand out, kinda cool looking but also an eyesore. I need to cover it to put the back seat back in. Then it'll look almost normal. Except for those subs in the middle of the back seat.
I was just kidding you. I sure enjoyed my stereo system in my truck when I had it. I just put a CD player in my car and am now thinking of putting some filters on the speakers to limit that "blap" sound when the bass notes are strong. I am also thinking of putting in a small sub woofer just to round out the bottom end. I was sort of hoping to find a small one to sit under the passnger seat.
If I remember 133 microfarad caps should be about the size you want. With some really good mids and highs an 8 inch sub under that seat wouldn't be that bad an idea. If you could make it fit. Can you find 1/2 inch 12ply marine grade russian birch? My dad made me remember this when I was about 8,"High distortion with low power will kill speakers before low distortion with high power." Those subs will get 700watts a piece of good clean orion power. I got to get this done before school starts or I wont have time for anything. Too bad I drank myself into a stupor last weekend in detroit, haven't got much done since last pics.