Recently, I built a small subwoofer (well, a woofer is more like it), using a Parapix Amp and a 8 inch Madisound 81524 DVC woofer. I designed the box to fit exactly to the dimensions of the Amp so as to take up minimum space under my desk.
The use of a dual voice coil (DVC) driver works especially well with the Parapix Amp since it has two outputs.
I put a fancy grillcover on it and rubber feet on the bottom. Construction is entirely from 5/8 MDF. The driver mounts in a 7 inch hole in the middle of a 12 inch baffle. The baffle board mounts to the back of a 10 x 10 inch hole in the side of the box. The box is lightly (but completely) stuffed with fiberglass insulation.
The volume of the box is just .85 ft3. The plans for the box shows how the driver mounts in the side and the Amp mounts into the end. This makes a very compact system that easily slips into the footwell of most computer desks.
These two curves represent the close-mic'ed output of the 81524 being driven with the stock Parapix Amp at it's minimum and maximum low-pass crossover settings.