Plasma speakers have been around in science labs since the 1950s, but that doesn't make them any less amazing in the 2000s. Like a standard speaker, plasma speakers work by creating compression waves in the air. But unlike a standard speaker that uses magnets and paper/plastic/etc to drive these compressions, plasma speakers are using the non-gas, non-liquid, non-solid "fourth state of matter" plasma.
What can be tough to see in these demonstrations (the first is the completed setup, the second is an FM-based prototype) is that pitch is altered by the constantly shifting intensity of the plasma arc (the creator puts the frequency response range at 200Hz to 12kHz, and the speaker runs at 50W).
So are these beauts for sale? From the creator:
A lot of work to do before I could consider selling - the safety aspect for starters.
Apparently someone needs to send this guy the memo. The danger is precisely what makes plasma so freaking cool.