Here's a quick video from the equalizer mobile I got to work on with the fantastic Sudhu Tewari.

As one can see, this mobile uses a fourier transform of the incoming sound to visualize the frequency make up of the music in the space.

Here can one can see how the mobile is set up as a grid - each row is mapped to a specific frequency.

All of the electronics are hidden behind the mirror side of the mobile, so when its hung from the ceiling, these are hidden behind the mirror panel.