An electroacoustic capsule or electroacoustic transducer for an electroacoustic device has electrostrictive or magnetostrictive elements connected to a controllable power supply. Dimensional changes of the electrostrictive or magnetostrictive elements cause changes of the inner geometry of the electroacoustic...http://www.google.com.au/patents/US7289638?utm_source=gb-gplus-sharePatent US7289638 - Electroacoustic microphone
