Acoustic feedback elimination circuitry for loudspeaking telephone - uses frequency detectors controlling level of attenuation device

摘要

The acoustic feedback elimination circuit for a loudspeaking telephone uses a frequency detector (14) coupled to the microphone and a second frequency detector (16) coupled to the loudspeaker (12). Their output signals are coupled to an AND-gate (18). The microphone (10) and/or the loudspeaker (12) has an associated level attenuation device (24) responding to the output signal from the AND-gate (18). The frequency detectors (14, 16) have a response frequency corresp. to the acoustic feedback together with a feedback response level. Pref. the level attenuation device (24) is an electronic potentiometer. USE - Loudspeaker telephone or entryphone.