A spectrum analyzer is a pretty useful tool for working with signals where the size of the frequency components matter. Usually, the display is a screen. Sometimes, you see it done with LEDs. [Mag Laboratories] did it with ping pong balls.
The device uses a processor to calculate a Fourier transform, cutting an audio signal into 16 frequency bands. The processor converts each of these values to a PWM output that drives small fans. The fans blow the ping pong ball up the tube proportional to the fan speed. You can see the result in the video below.
Of course, as you might expect, the response time of the ping pong balls isn’t going to match the response time on an LCD, but this isn’t meant to be a practical tool, as much as a piece of electronic art. It would be interesting to see this done on a larger scale with some lighting for use at a concert or a dance floor.
Thanks for the tip [itsthatidiotagain].