The Solar Sounder is a box with an analogue synthesizer and a speaker in it. Without batteries, the unit changes its sound under the influence of sunlight, shadows and clouds. Referring to the undertone chant of Gyuto monks, the Solar Sounder emits a low frequency voice.
"The art is not in the action of playing them, but placing them in the sun and listening," wrote Peter Blasser who designed the original circuit. Each Solar Sounder is different. This is my take on Blasser's self-bending tool.