Ping Pong Spectrum Analyzer

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.

Last month, we looked at a cool 3D analyzer that used LEDs. For audio, of course, you can always use the soundcard or plug in an RTL SDR device for RF.

Thanks for the tip [itsthatidiotagain].

10 thoughts on “Ping Pong Spectrum Analyzer

  1. Perhaps a piece by Blue Man Group, the bonking of undamped response decay is distracting to say the least. Make the pipes a musical scale and then figure out the timing to make them play in time, good luck. There should be a long term averaging going on each channel to make this really show something. Balls should mostly be at some level not moving.
    Like the LED candles having music as the “random” in their effect, this could do the same. Any music. There would be no loss in “information” anymore than those screen players that show random lines bouncing up and down and have nothing to do with the file playing. I couldn’t tell which end was bass.
    Thanks for not calling it an EQ.

  2. It would be interesting to see this implemented with a more ‘constant’ air supply piped to each tube with a ‘proportioning’ valve used to control the air flow, similar to the way a pipe organ is fed with a regulated but constant flow of air. Feedback could be provided with an IR distance sensor to give stable position. This would likely help with the slow response and unstable position.

    Still a really great implementation though!

    1. Without position feedback in a cylindrical tube, you have no way to know where the ball is in the tube. You have only an estimated position based on fan speed, time, estimated history, and that gets worse over time.

      A rotameter works by raising a float inside a slightly conical tube (pointy end down), with the result being the float position is proportional to airflow. As the float rises higher, more air leaks past it. Assuming air flow is proportional to fan speed, the float position would be proportional to fan speed.

      To emulate a conical tube, drill identical holes in the tube about 1 ping pong ball apart. As the ball rises, more air leaks out, limiting the ball height for any given airflow. You start with small holes, then enlarge them to find what works in your system.

  3. While there are better solutions out there to fix the response time – simply delaying the audio playback by a second or two so that by time the user hears the audio the ping pong balls have had a chance to adjust position, would make the display a little more enjoyable. Nonetheless a very cool combination of Art, Music, and Science.

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