Electroacoustic system with electronic filters

An electronic filter for an electroacoustic sys­tem. The system has a microphone for generating an elec­trical output from external sounds and an electrically driven transducer for emitting sound. Some of the sound emitted by the transducer returns to the microphone means to add a feedback contribution to its electrical output. The electronic filter includes a first circuit for elec­tronic processing of the electrical output of the micro­phone to produce a filtered signal. An adaptive filter, interconnected with the first circuit, performs electronic processing of the filtered signal to produce an adaptive output to the first circuit to substantially offset the feedback contribution in the electrical output of the microphone, and the adaptive filter includes means for adapting only in response to polarities of signals supplied to and from the first circuit. Other electronic filters for hearing aids, public address systems and other electro­acoustic systems, as well as such systems and methods of operating them are also disclosed.