These loudspeakers can defy gravity

Here is a great YouTube video of Dr David Deak's 'Acoustic Levitation Chamber'. Using three loudspeakers in a plexiglass cube, he can make little paper cups fly around and control them in three dimensions. He did the project while working for NASA in 1987, and is now an artist. On a similar subject, If you enjoyed the resonance videos mentioned here, you'll probably enjoy this. (thanks, Bryon)