This page describes my technique for building fiberglass subwoofer boxes. I’ve built 5 subs this way and the results are good, but it’s a lot of work. This particular one is for an Acura RSX.
The technique I use involves covering the area with plastic, then a layer of fiberglass, followed by chicken wire. I use tape and wood sticks to hold and prop the chicken wire in a few important areas. I have been told about another technique involves covering the area with painters tape, and spay glueing the fiberglass to the tape. I shyed away from that tecnique because the heat from the fiberglass resin makes it hard to clean up the tape. Also, I am paranoid that some resin might leak through the tape seams.
This picture shows the glass after the resin has been applied. One unfortunate thing about this tecnique is that the first layer of glass doesn't always stay in the right place after resin is applied. The resin is heavy and the glass loses its stiffness while the resin is curing. If you use this tecnique, expect to have to cut away some areas and make patches after the first layer is cured. I didn't show any pictures of that, but rest assured it was needed for this job.
After the first layer is cured, I remove the glass from the car, remove the chicken wire, and clean up the interior with a dremel tool. You'll want the interior to be pretty smooth for the next layers. This is the time to make any repairs and adjustments. I normally have to cut away a few small areas. Patches are easy to make. Put more plastic in the car, put the glass box in place, and place small pieces of dry glass behind the cut away areas. Resin the patches and repeat until you have the shape you want.
With the first layer patched, I remove the box again and add more layers of glass whith the box sitting on a table. Depending on the glass thickness of the first layer and the box shape, the first layer of the box might be too flexible. Sometimes I add the second layer of glass while the box is in the car. The third (and more) layer(s) can be done out of the car. I usually go for about between 1/8 and 1/4 inches of thickness.
The inside of the car had a little indentation at the bottom of where the sub would sit. I cut a piece of wood to fit in this indentation, rather than just letting the glass form the shape. My intention was to make the weight of the sub box, coupled with the tight fit of the wood insert, pin the woofer in place.
The front face of the box is cut from 3/4 inch MDF. Creating the shape is as difficult as any part of this project. Unfortunately, I didn't take any pictures of the process but it generally involves making a cardboard template, cutting out the basic shape, and going back and forth between the car and a belt sander until the face fits perfectly. I generally leave about 1/8 inch gap all the way around to allow for carpet. This picture shows the woofer hole cut and the mouting surface attached to the inside face.
From the back, you can see the woofer mounting surface is just another piece of MDF glued and screwed to the back side. Here you can also see that some of the face edges were beveled with the belt sander to contour to the car.
Attaching the face to the box is accomplished by laying in small strips of glass from the inside and the filling in from the outside. This picture shows the box upside down after the final layers of glass were applied to seam the face to the box.
During construction, don't forget to plan the bananna plug location. On this box, I resined it in from the inside.
And once again, after carpet is installed. Actually, I think it's called trunk liner and I get it from my local car audio shop.