Four bouncy balls suspended by slinkys above four loudspeakers. The top of the slinky is attached to an acoustic amplifier (basically a plastic cone) whilst at the bottom the balls bounce up and down on the loudspeaker cones when powered via wind up torches. The sonic result is something between confused Morse code on an old telegraph and a 1950’s sci fi laser gun battle.
This video documentation from the BV open studios event in Bristol in 2011
The basic principle of operation is a kind of electro mechanical feedback rather like how doorbells used to work before this current age of ubiquitous bleepers and buzzers. This circuit is also sometimes referred to as the ‘victorian synthesiser’ . See schemeatics below