SolidDrive: Invisible Speakers
SolidDrive allows you to turn most solid surfaces into speakers allowing you to utilize walls, glass, or countertops already in the room to create a virtually invisible sound system. Hooked up to an amp, the device can be installed behind walls and by converting audio signals into vibrations the entire wall can be turned into a speaker with omnidirectional sound covering most frequencies.
Not really geared toward audiophiles, SolidDrives still produce commercial quality sound and uses very little power. It uses a compound called Terfenol-D, a sort of rare-earth magnet that was declassified by the Navy. For more info including purchasing information visit SolidDrive. Professional installation is recommended for EQ setup.