[Carey Carlan]

A program on TV about refrigeration with sound waves got me reading.

A navy project has created a refrigeration system that uses acoustic waves
to move heat down a tube, creating a warm end and a cold end, IOW a
refrigerator. One example used a device that produced an effective 190 dB
level within the tube. Another, more current, device uses 10 KW of power
at an 85% electric to audio (electracoustic) conversion efficiency. Damn.

There's absolutely no link between our speaker drivers and these devices
beyond the fundamental physics, but wouldn't it be cool to have a speaker
work at 85% efficiency? You could practically run your stereo off a 9V
battery.