There's a slight flaw though.... it just channels sound around, not actually damping it, so you couldn't create a soundproof room, just a room that didn't have any external noise- good for recording, but not for the neighbours, as they'd still hear you.... unless the surface is unidirectional, in which case it'd be horrible for recording, because the sound waves would never leave the room, so you'd end up with standing-wave city!
Quite a cool idea for things like radar and such though, to make something appear acoustically invisible :)
