Peter wrote to tell me about the Eminent Technology Model 17 fan-powered subwoofer. It's all well and good, but I'd personally go for this one-off 60 inch subwoofer: "The cone moves 6 inches peak to peak under full-tilt output... Unfortunately, Tim and his crew didn't realize just how much acoustical power the sub could generate, and didn't build the vehicle to contain it appropriately. Even at less than 1/2 output, the doors were blown off the tracks, and the entire vehicle ballooned in and out several inches."