355 Footwell Subwoofer

Next step is to cut out a face. For most boxes, just a simple ring is easiest. For this one, I wanted a larger wood face because I think it will make the carbon fiber facia I want to do easier. I traced the box onto a piece of wood and then "shrunk" the trace by about an inch all the way around. Then I cut out the face and the woofer hole.

Next I attached some temporary support struts (wood dowels) with hot glue (easily removed) to the face to support it in the fiberglass. Then I glued the other end of the struts into the box, so now we have a face we can start to attach.
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Well, a lot of the recent steps can't really be seen, but here's what happened since the last update. The woofer face was just slightly out of alignment for what I needed. Rather than pull the face off and re-glue the dowel rods several times in hopes of getting just the right rotation, I applied a couple of pieces of duct tape to put a little rotational pressure on the face and that worked well. You can see the duct tape under the black fabric in a couple of spots.

I then sprayed the face and the box edges with 3M Super 77 adhesive and stretched the same black jersey fabric we used earlier over the face of the box. Once the adhesive had dried, I painted the fabric a couple of times with the epoxy resin which made it very stiff and sufficient to hold the wood face in place. I trimmed off the excess fabric and pulled the dowel rods out of the inside of the box (the hot glue releases quite easily).

You can see from the photo that there are some relatively hard edges around the wood to the fabric. Fiberglass doesn't like to lay into sharp edges like that, so I mixed up some more fairing compound (same epoxy resin with a dust-like additive) and filled in all those areas behind the fabric to make a smooth transition to the wood. The fairing compound is messy, but when mixed right it's like putty and will stay where you put it.

Obviously the fairing compound edges will be pretty rough when they're dry because I had to do the whole thing blind since they're inside the box. Tonight I'll take some rough grain sandpaper and smooth things out as much as possible. Then we're only really one step away from being able to listen to the result - additional fiberglass has to be put in to thoroughly bond the wood face to the rest of the box and seal it up airtight.

At that point, I can put the woofer in the box and the box in the car and at least listen to the result. But there will be two cosmetic steps left after that before the project is actually finished.
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This morning I was able to layer in the fiberglass to bond the face to the rest of the box, so when I got home it was ready to test fit!

To protect the leather in the car, I took a dremel tool with a little grinding wheel and spent some time de-burring the box - grinding down the little resin, cloth, or fairing compound spots that had hardened into sharp edges here and there. Next I put a flannel towel over the center console to protect that leather. It took a little work to get the box in there, but once it popped into place it fit like a glove. The fit is fantastic - as you would expect having molded the box off the car. It is a very tight pressure fit, so I have no fear of the box being able to move, even under hard driving. I would certainly take it out for track days, but for hard street driving it won't be going anywhere.

I was then able to put the woofer in and line things up so the woofer logo would be oriented correctly before drilling the mounting holes for it. As you can see from the side shot, there's still plenty of footroom left. I was able to sit comfortably and I'm 6'3" with size 13 feet. I would likely remove it for a road trip, but around town a passenger would have no problems.

Next up - test listen!
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Sorry to take so long getting back to anyone. For better or for worse, the project got to the stage where it was a heck of a lot more fun to drive and listen than it was to finish the aesthetics, so that's what I've been doing!

It took a few hours of driving and listening and tuning to get things to sound the way I had hoped they would. I'm crossing the sub over higher than I normally would (about ~125 hz) because the OEM door speakers are pretty heavily blocked by the door panel, so they don't put out much useable midbass. After fooling with the levels in the amplifier, I've achieved a balance I'm very happy with.

It's not quite as punchy as the dual 10" setup I have in my Testarossa, but it sounds quite good and is listenable into triple digits with the top down. Not audiophile at that point, of course, but listenable. At slower speeds or with the top down it sounds quite good.

Unfortunately the OEM head unit doesn't have any significant EQ past bass and treble controls. My higher end Alpine and Pioneer units in other cars let me do sub tuning that really makes a difference. I may eventually change this head unit as well since I do most of my car listening from an iPod anyway. I bought one of the Alpine iPod-only head units for the TR but haven't put it in yet.

So, the good news is I'm very pleased with the end sound and the amount of room I lost to the sub. I do still have some finalizing to do on the aesthetics. I want to round the edges of the face a little more with Bondo and then try the carbon fiber fascia. However, it may be a while before I get to that since I'll be moving houses in the next couple of months.

I have not yet done a mold for it, but I'm not past the point where I can. That's still a possibility after I get to the new house.