This is pretty cool stuff.
“Cymatics (from Greek: ???? “wave”) is the study of visible sound and vibration, a subset of modal phenomena. Typically the surface of a plate, diaphragm, or membrane is vibrated, and regions of maximum and minimum displacement are made visible in a thin coating of particles, paste, or liquid. Different patterns emerge in the exitatory medium depending on the geometry of the plate and the driving frequency.” from Wikipedia