I can remember a friend of mine telling me that one could make sub with a pulsating balloon.
You'd fill up a balloon, a really large one, put it in a chamber and attach many many voice coils and magnet assemblies.
Then you could controle how it changed shape and make a omni sub, sort of a pulse sphere driver.
We did it on paper I believe, but we never built it. It's a great idea I'm sure..

He's a theoretical physicist by the way, he would all the time tell me that my ideas were way off.
And then one day he came up with this... aa balloon sub. Dang, we should'a built the thing!

There was something about a pneumatic valve system that would work in tandem as well, making it inflate and deflate
really quick.
Back in the 90s Cervin Vega built a sub using a foam type screw shaped object that moved in a cylinder.
It's amazing what will work! The Vandersteen sub driver, the Tympany sub driver, there are alot of cool sub drivers out
there not neccesary looking like one...
Nanotube drapes acting as subwoofers... now wouldn't that be a lifesaver for any system?
Imperial