It's been a few years since I had a subwoofer in my car, and I wanted to make sure I got this one right.

I looked at various offerings and designs, and made up my list of requirements:

• must not be in the trunk - too much sound pressure difference with the top up or down, and I won't eliminate the spare tire;
• as this is my daily driver for work, the trunk holds my laptop and large tool bag, and I can't loose the pass-through under the rear window;
• I have kids that may ride in the back on occasion, so the rear seats must stay;
• have a 'stealth' appearance - the interior of the car remains stock except for the seats and roll bar;
• sound decent;
• affordable.

That last point dictated that I build the box myself.

The best spot appeared to be the space occupied by the rear seat cushion; by using up the space under the folded rear seat back and the space behind the seat, I could make a box approaching 1.3 cubic feet.  The seat back would stay in place, covering the box from view, and if the rear seat is needed, the box could be lifted out easily and the cushion dropped back into place.

I started by removing the rear seat cushion behind the drivers seat, and mocking up the proposed box in cardboard.  With the maximum dimensions double checked, I glued and screwed together the base for the new box, and fiberglassed the bottom of the box in place.

I put on nine layers of cloth on the inside.  Lifted out of the car, you can see the gap between the 'glass and the outer edge of the wood; I filled this with automotive body filler, and applied three more layers of cloth to the outside, carefully cut to minimize wrinkles.  I sprayed the inside of the box with umpteen layers of rubberized undercoating, smelling up the garage for a week.

The front of the box is a bit longer than the cardboard template, to allow for the depth of the driver.  A 10" driver was recommended to me for the box size, and that's all I really had space for on the front of the box.

The driver was selected, which helped place the front side of the box.  The computer modeling of the vent dimensions was done by my friend at Audiophiles for Audiophiles.  Slot vents are cool. The driver was chosen for its ability to function properly in small boxes.

I added internal bracing, horizontal and vertical, to minimize flexing of the sides and lid.

A close-up of the vent. The vertical brace under the corner of the vent holds the vent in place against the lid during assembly, and after provides stiffening to reduce flexing of lid.

The lid is glued and screwed in place, and the countersunk holes are filled and sanded.  Here you can see the outer layers of 'glass and resin that go right up the sides of the box.

I cut the lid slightly oversized, and used a belt sander to make the edges flush.  A router with a 3/8" radius bit rounded the corners nicely.

A red top battery and fuse holder next to the main fuses. The amp sits under a false floor in the trunk, along with the stiffening cap and the compressor for the air suspension. More pictures later on this.

A can of Ultra Flat Black spray paint for the appropriate 'stealth' look.  I made a gasket using some thin closed-cell foam for the driver.

Looks good so far.

A 10 gauge quick-disconnect takes the signal into the box through the front wall of the box.

With the seat in place, the box disappears from view.

The final internal box volume, before taking away space for the vent and driver, was 1.22 c.f.

After a week of tweaking and letting the driver break in, this thing rocks.  I am very happy with results, although my LoudMouth exhaust doesn't seem so loud anymore....

Last edited Friday, March 23, 2007

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