I know some guys that played with SI sound pads using Fed Ex shipping cartons and some other semi-rigid materials. They were impressed with the sound, although they can't go very loud.
I believe that was bubba966 who had them.... 
Henry is talking about Ed and a buddy of his. After they'd played with 'em a bit Ed sent me a pair of the NXT transducers.
I played with 'em & FedEx boxes for a while. Damn impressive. Couldn't believe what I was hearing from a $20 pair of "cardboard boxes". So good that a roommate picked up a few pairs for a 5 channel FedEx HT setup. I also had a friend over. Played her a Sarah McLaughlin (sp?) song w/out telling her what she was listening to. She was pretty impressed and said that while she's heard that song many a time (turned out to be one of her fav's), had never heard it sound so clear and heard things that she's never heard before.
Then I told her she was listening to the FedEx boxes sitting on the floor...
She didn't quite believe it until I picked up the box and handed it to her while something was playing.
She still wants to replace the speaks in her living room with a pair of NXT's mounted on some foam core. Will have to get to that someday.