two independent feedbacksystems running simulataneously and interfering with each other.
the first consists of an open microphone surrounded by two hairdryers with rubbergloves, blowing randomly. the microphone feeds into a filter controlled by an enevelope follower and sounding thru a loudspeaker.
the second feedbacksystem is a viola with a transducer attached to its body.
the microphone is a piezo disc on the tip of the bow, which also picks up vibrations from bowing on the strings.
neither system is insulated against the other.