I discovered a most unexpected sound source during my formative years while working part-time in a local hotel.

Back in these days ice-cream used to be delivered in massive cases with huge dollops of frozen carbon dioxide inside to keep the ice cream cold. Frozen carbon dioxide is of course the stuff known as "dry ice" much beloved by rock bands for producing smoke/mist effects when immersed in water.

Anyway, I discovered that if you take a metal dish and hold a piece of frozen CO2 against it, it produces a shrill sustained screaming note. I conjecture that the ultra-rapid cooling sets up a vibration in the metal.

It would surely not be beyond the wit of man to construct a keyboard operated instrument with different sized dishes ???

Murray