NPR covered a story about the Paper Concerto, an orchestra performance with instruments made of paper. Within the segment, they featured a musician called David Cossin, who has created an instrument called the Amplified Cardboard Tube. From what I gather it’s cardboard that has been smashed on one end to soften, with a microphone inside the tube and a speaker outside of it. This creates a feedback loop that can be controlled in terms of pitch or, more simplistically, a singing drum.
There are a few links where you can listen to it, both at NPR’s site and David Cossin’s own site(click MUSIC).
It got me wondering, can one create a visual feedback loop? Two giant mirrors set parallel to each other with a laser light bouncing back and forth in a fog shroud that captures a “light object” within.