Custom Fit Subwoofer Box

Written by Mike Napurano, Member 1
Applies to the following vehicles: 97-03 Grand Prix
Created 10/15/1998

Write-Up Rating
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Written and submitted by JC Hoefer

After wrestling with the idea of loosing my pass though, I decided to design a box that would conform to the specifications of my subwoofer, while retaining enough space to have a usable trunk and pass-thru. First I measured several possible areas in the trunk to install the box. I had though about using the space in the trunk behind the wheel well on the passenger side. Finally I decided to place it flush against the driver's wheel well and the back of the seat.

This posed several difficulties because of the angles of both sides. So I wrote down tons of measurements, from every conceivable point, and started sketching the prototype. After finalizing the drawings in CorelDraw, I created a full-scale prototype from foam board. Using this prototype, I checked for fit in the trunk.Luckily it was perfect.

Sub Box Plans: This ZIP file includes the plans in PDF, DXF (AutoCAD), and CDR (CorelDRAW) format. The plans are just of the various parts.

I took the design to a printer and had full-scale "blue prints" printed out. These would be used to measure out and verify the cut pieces of the box. Then I cut out all the pieces.Assembly went very quickly. Starting with the front, I attached all the sides using nails and Liquid Nails (as a sealant). This picture shows the sides and the recess plate before the rear panel was attached.

After letting the box dry for an hour or so, I attached the rear panel. Then I let it sit for another hour. After that I coated all the joints with an extra layer of Liquid Nails and let it cure overnight. These pictures show the front and back of the box after final assembly. Note the recessed subwoofer mount.
Carpeting the box was a real pain because of all the compound angles. In one place I had to scab a piece in, however, you would never know by looking at it. Because of the thickness of the carpet, the subwoofer was a tight fit. But looking back, I wouldn't change it because it creates an airtight seal. These pictures show the box carpeted and wired, and the crossover. The crossover is visible within the box.
Before I started wiring the car for power and signal, I checked to make sure the box would fit. I expected to take out the driver's side 6x9 to maximize the interior volume of the box. It was a very tight fit, and the box really should have been 1/8" - 1/4" shorter. I had to push the box under the rear parcel deck, but otherwise the fit was perfect. You can see in the picture below that there was no wasted space. This was taken with the back seat and rear deck removed.
I used the wiring harness entry point (passenger side firewall) to bring the 8 guage StreetWires in. This step alone took nearly an hour with the car jacked up and me on my back. I routed it along the doorsill and up into the trunk along the passenger side.

Then I connected the main power connection into a 30amp fuse and holder bolted to the firewall in the engin compartment. The supply came from the auxiliary 12v power connection on the passenger side strut tower. I used the antenna amplifier power connection for the remote power on, and grounded the amplifier using a new self-tapping bolt.

Mounting the amplifier was difficult, but I ended up using the method by John Tsimaras (thanks John!) on the Grand Prix Net, which is a mounting plate against the seatback in the trunk on the passenger side, which is opposite the subwoofer. Because of the tight fit of the subwoofer box, I ended up trimming the trunk floor mat around the box (I told you it was a tight fit!) and clipping the rear seat support (1 of four) 1/2 inch shorter, which didn't affect it's effectiveness. But it actually makes the installation look better!

The pictures below show the completed (well nearly) installation from several angles, including the back seat.
My only regrets are : The color difference in the box covering material (as compared to the factory carpet); And that I didn't do it sooner.

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