Custom Woofer Box Construction
To get the best quality bass possible without sacrificing the trunk or the utility of the versatile MkIII hatchback design.
I lived with the stock radio for much longer than most people (on the order of around 8 years). In an effort to keep everything as stock as possible I even upgraded to the stock top-line unit and went from the AM Stereo/FM Stereo/Cassette which came with the car to the AM Stereo/FM Stereo/Cassette/CD with separate amp. I got this from Rob C's 1989 which he had parted out. This unit was good and satisfied me for another couple years (amazingly) but then finally the CD player started acting up and the whole unit started getting a little flakey sounding compared to some of my friend's aftermarket systems. That's when I got hit by the upgrade bug.
As usual, I went first class with everything. Eclipse's top-line 5303R head unit (with full ESN security) with a PPI450 (200W) powering the main speakers and a PPI2400 (400W) for powering the sub. The first thing I did was spend a weekend running some 4-gauge power wiring to the rear and all the power splitters, fuses, speakers and ground wiring. Then came the head unit up front and the main system amp. But I digress... the point of this page is to show the work in building a subwoofer which didn't eat the trunk...
First off, I went into a design phase. I took measurements and came up with the following preliminary design:
My goals were simple, but difficult to create it looked like. I wanted to maintain as much trunk space as possible and keep using my Cusco OS rear shock tower bar. I wasn't ready to sacrifice structural rigidity for bass just yet. I also wanted it to look as stock as possible, so it was to fit perfectly in the back and be carpeted in the same gray carpeting. Lastly, I wanted to maintain the utility of the hatchback design, so the whole thing had to be easily removed if need be. Sounds easy huh? Not...
From there I brought it to some of the best custom stereo guys in the business, Innovative Audio. The name really does say it all. The guy who worked on my car, Sean, has about 15 years in this business and his portfolio of work is really impressive. I figured he could easily handle my job. I was right.
He took my design and was able to build a box which could handle not one, but two PPI Pro08 carbon fiber/Nomex flat piston drivers! I was happy. These two eights could belt out enough solid, tight bass to allow me to play just about anything I wanted and loud enough to damage my hearing :-) Thus, we started out on building first a ported and then finally settling on a sealed enclosure for maximized bass accuracy without "boominess".
Taped Up/Prepped Supra
PPI Pro08 Woofer in Hand
PPI Pro08 Woofer
After taping up the rear of the car to protect the finish from scratches or rub marks, he started by laying out the entire rear part of the design in fiberglass to perfectly match the contours of the rear floor and seats.
Here's what it looked like in a roughed out form:
Fiberglass Roughout (Front)
Fiberglass Roughout (Back)
After cleaning everything up, the front section was made out of a lightweight but strong compressed wood product and fitted to the fiberglass such that a notch was left across the top for the cross bar to sit in. It was then carpetted with matching gray material to completely match the trunk. I had the option of a vinyl-based covering, but I thought this would be much more durable and look cleaner.
Roughed Out Box Clearance Check
Carpetting to Match
The installation was very tight. In fact, there is only a few sixteenths of an inch clearance from the massive magnets to the fiberglass on the inside. There was lots of exacting work done here to maximize the minimum amount of space we had to work with. The good thing, from a security point of view, is that thing probably won't even fit in another Supra. It's that customized.
The Final Product
The final product was well beyond expectations. The box is an absolutely perfect fit between the shock towers and the pins keep it from moving at all under any accelerative forces. All connections were made with 24k gold plated connectors and the whole thing is hooked up the best Monster Cable has to offer. The piece de resistance of this thing was the custom grille he created to cover and protect both speakers. The following pics show the final result prior to installation:
Woofer Box (Side)
Woofer Box (Front)
Woofer Box (Rear)
Woofer Box Lock Pins
24k Gold Connectors
Once installed, the lock pins lock into specially made channels made in the rear subfloor hinge frame and keep the box from ever sliding forward under acceleration. This thing is designed to easily withstand quarter mile drag runs without putting a dent in the back :-) Also, the design allows for access under the subfloor since the box doesn't go beyond the hinge point of the floor. Thus, the spare, the amps, the fuel gauge sender, etc. are all still easily serviceable without having to remove anything.
Here's what it looks like installed:
Plenty of Trunk Space Left
Beautiful Cusco OS Bar Still Visible
Side View is still Trick
The design may impinge upon those with targa tops wanting to mount the roof in the back, but that issue didn't concern me here. But if I did have a hole in my roof, the second design I contemplated involved a countersunk twin 8" downfiring sub (or a single 10"). This would have provided more clearance to the bar and would probably fit underneith the targa roof when mounted. For me though, sound quality is the best this way for a hatchback since the back of the hatch acts basically like a cone and reflects the sound back to you (think of a reflector telescope). Also, since you want to get a good standing wave pattern for good bass, this fulfills that aspect as well. On the other hand, a downfiring sub would give you an extra surface to bounce off of (which is good in most cases), so it might be something to think about for targa people...
Once everything was plugged in, we tuned the crossovers using a digital tone generator which would create solid or sinusoidal tones within a certain frequency range. This allowed us to keep frequency overlap within an acceptable range and keep the main speakers from ever having to reproduce serious bass again. Then it was further fine tuned by ear since this kind of stuff is pretty subjective.
While the final results are not enough bass to hear five miles away (more like one or so :-), that's not what I was going for. To make tight, clear bass for pop, classical, jazz and rock (the stuff I primarily listen to), you need to spend a little more for quality hardware. This is one case in which bigger isn't necessarily better since the bigger you go with speakers, the more heavy duty your magnet has to be to overcome the higher inertia of the larger cone. These twin 8s are incredible though and on par with many 10s in my opinion. The bass quality of these flat piston drivers is extremely tight and accurate. I can easily make myself deaf if I want to with over 600W of sound here, but again, that's not the point. The point is that I didn't take up my trunk completely and still ended up with a damn good sounding system, if a little bit "customized"... :-)