Watch on HDtoday. For Lucinda Child’s VEHICLE, Peter Hirsch designed a 70 kHz Doppler sonar system. Childs swung three red fireman’s buckets around inside the ultrasonic sound beams created by transmitters hung on scaffolding. As Childs swung the buckets, the reflected signals mixed with the original 70 kHz signal, and the resulting beat frequency fell in the audible range. These sounds were transmitted to the twelve speakers around the Armory. [Overview courtesy of Anthology Film Archives]