I listen to a lot of dance music which contains a fair amount of bass which, unfortunately, is difficult to reproduce with a small speaker. I thought about putting a subwoofer in my Spider for quite some time. They add a whole new dimension to music; they have more low-frequency range than any 4" or 6" speaker. While riding in friends' cars that had subwoofers, I found myself saying, "Whoa! I've never heard that before" when listening to music. However, I was having difficulty deciding where to put one. Again, I didn't want to sacrifice the back seat space, and the shallow trunks make it difficult to fit any type of subwoofer enclosure in there (except maybe something small like 8" subs).

The answer was to be found in, of all places, a Mustang. My manager at Autodesk had created a custom isobaric subwoofer setup for his '92 Mustang, which slipped into the spare tire well. He was turning his car into an all-out track car, so he stripped it of its stereo. Since I we had become good friends (and I had been such a dedicated intern working on the Mustang Project ) he gave me his two 300W Pioneer 12" subs for my birthday.

The subs were mounted in an isobaric configuration (they faced each other, mounted on a baffle board). The polarity (+/-) of one of the subs was reversed so one sub would "push" while the other "pulled." This allows you to get twice as much power out of a given volume of space. I removed my spare tire and screwed & siliconed a partition between the spare tire well and the gas tank. A sealed/airtight space is needed for the subwoofers to sound right (they have an optimum volume to operate with) so I sealed up all the stamped holes in the tire well with a couple layers of aluminum heater/air conditioner duct tape. I wasn't sure this would hold up, but when I later removed the subs it was still intact.. I then cut the baffle board (just a flat board) to shape and screwed & siliconed that down. I powered the subs with a 300W amp (not really enough power for the two subs, but still good). A six-speaker setup in a small convertible isn't bad at all! I tested it out with one of those ultra-bass CDs and the car vibrated so much the exhaust, bumpers, and windshield rattled! I never cranked it up that much during normal operation, but it was worth a good laugh!

I forgot to take pictures of the subs in the car when I had it, so here are some AutoCAD images...