Here is an audio subwoofer that uses a new way of generating sound. This subwoofer uses a rotary design to spin at high speeds and generate very low sound frequencies at downwards of 5 hertz or lower. Frequencies of 5 Hz is almost unheard of from standard cone shaped woofers. A standard speaker design does not allow the freedom of fitting in small spaces either. This rotary speaker design uses the same effect that occurs on a propeller driven aircraft. The propeller blade’s tip generates sound as it spins in air and the sound frequency is controlled by the pitch and speed of the propeller blade. Although this particular design is patented, I would encourage you to experiment with various home grown design that would be fun to play with. Hooking propeller blades to high speed servos to rotate the blade pitch should give you the desired frequency you want as long as you program it correctly. The Parallax Propeller chip can be programmed to handle the audio controllers added. Your rotary speaker design will be able to produce sound frequency waves that could create the ultimate home theater system. Not only that, if you designed your own home system, you could make the ultimate home audio control system that would perfectly balance your audio in your home. Your home audio theater system can be completely designed and controlled with the Parallax Propeller chip. Maybe you could even make an audio set up that would automatically balance according to where you were sitting in your room. Now that would be the ultimate home theater system! Perfectly balanced sound at every frequency in the spectrum. 
Rotary Woofer (Eminent Technology)