In the past we have specified Solid Drive transducers to turn wood, glass or drywall into a speaker. They are quite expensive but very cool. $500 each retail.
I subscribe to Instructables.com and one of this weeks projects is Hanging Glass Speakers.
Same concept as Solid Drive, I don't think I would do it that way, but astounding for the inexpensive components that are used for the transducers and amplifier.
$20 each for transducers and $18 for a 20 watt stereo amp!
I have a customer that used Solid Drive to turn a living room ceiling into surround left and right speakers and a kitchen floor turned into stereo left and right.
I'm tempted to get the components just to play with.