An adaptive volume controlled radiotelephone system includes a microphone, a loudspeaker, a transceiver, and an adaptive volume control. The microphone generates an output electrical audio signal in response to sound, and the loudspeaker produces sound in response to an input electrical audio signal....http://www.google.de/patents/US5966438?utm_source=gb-gplus-sharePatent US5966438 - Method and apparatus for adaptive volume control for a radiotelephone
