Here is a woofer capable of reproducing DC - in normal sized rooms. Has quite a bit of DIY potential! http://www.rotarywoofer.com/
I still don't understand how this thing works? I understand the amplifier controls the blade pitch, and the motor is plugged into the wall. But beyond that I haven't seen a clear explanation. I guess likely to keep the tech propriatary.
No, it's not that complicated. Think of the fins twisting when they control the pitch. Sharper pitch makes the forward velocity stronger, less sharp makes it weaker, and when the fins are in line with their path then there is no velocity. Then when they twist in the other direction (past the in-line position), the fan starts to blow in the opposite direction and the velocity goes from positive to negative. The voice coil twists the blades which makes the air blow forwards and backwards alternately depending on the the twist amount and "polarity".
Ahhh, thanks Bill. That makes more sense now. That's why it has to have a separate air space. I thought the fan spun at 5hz. I thought, geez that's not going to push any air. Haha.
No, the fan spins pretty fast. Also makes a fair bit of noise, I'm told, so it has to be remotely located so the higher frequency noise can be dissipated in the duct.