This is a pretty cool video called 'The Amazing Resonance Experiment' done by a YouTube user known as Brusspup.
In it, he demonstrates a plate experiment similar to that of Ernst Chladni, a German physicist and musician in the late 1700s.
Chladni did a lot of research and experiments related to vibration and frequencies - many of which are still used today in the design and construction of instruments such as guitars, violins and cellos.
Some call him the "Father of Acoustics".
In this video, Brusspup puts a metal plate on top of a speaker, then hooks it up to a tone generator, and pours sand on the plate.
As he changes the frequencies, the sand moves around and forms different geometric patterns. And the higher the frequency, the more complex the pattern.
It is a fascinating visible demonstration of sound. By the way, you can also watch the original video with the actual tones, but be warned it gets pretty loud so keep your volume low.
And to check out more of Brusspup's videos, including Amazing Fire Illusion, Crazy Wire Illusion and Giant Dry Ice Bubble Experiment, go to his YouTube channel.