Pyro Board: 2D Rubens Tube.
"The pressure variations due to the sound waves affect the flow rate of flammable gas from the holes in the Pyro Board and therefore affect the height and colour of flames. This is interesting for visualizing standing wave patterns and simply awesome to watch when put to music."
Skip to 3:38 in the youtube clip to hear it with the music. The lo-fi track used to demonstrate is sick, and makes it that much more amazing to watch.
DELICIOUS FIRE SOUND WAVES HERE.