Ultrasound induced cavitation control with application to lithotripsy has been investigated. Previously, a two-frequency ultrasound combination has been proposed to utilize the violent collapse of the cloud cavitation. In this paper, the cavitation cloud collapse phenomena is investigated experimentally in more detail. The behaviour of the bubble cloud formation in the high frequency phase (3.88 [MHz]) is photographed. Then low frequency ultrasound (555 kHz, short pulse) is used to expose the various kinds of the cloud. Acoustic emission due to the bubble collapse is recorded with a Passive Cavitation Detector (PCD) and the response of the cloud to the 555 [kHz] ultrasound is investigated.