Many years ago in Speaker Builder magazine, a bass player used the round cardboard used to form concrete to build a cabinet. Used a 15 EV firing down into the tube, figured the volume needed for the height of the thing, and the rear of the speaker radiated 360 degrees. Seems he had a baffle at the top(rear) of the driver. Said he gigged with it a lot, and worked great for bass,(non-directional anyway). I always wanted to try one but never did.