This is the most amazing thing I’ve seen all day! Stop and watch this video right now. Brusspup, maker of astounding optical illusions, let water flow past a speaker set to a particular frequency:
Run the rubber hose down past the speaker so that the hose touches the speaker. Leave about 1 or 2 inches of the hose hanging past the bottom of the speaker. Secure the hose to the speaker with tape or whatever works best for you. The goal is to make sure the hose is touching the actual speaker so that when the speaker produces sound (vibrates) it will vibrate the hose.
via Neatorama
March 13, 2013
This visual effect only works because the camera is sampling the light from the scene at 25 Hz.
If you want to see this in real life, just illuminate the scene with a stroboscope pulsing at 25 Hz (or 50 Hz). Then you will see what the camera sees.
It is the Doppler principle, as used in testing your car’s ignition timing.
Yeah, odd that they didn’t choose 30Hz, since more modern video cameras default to 30fps, and 30Hz would have been easier for a speaker to reproduce. Wonder what effect rolling shutter has?