Abstract: A speaker telephone for use with a two wire telephone system and incorporating an audio input circuit for receiving an audio signal to be transmitted over a conventional two-wire telephone system is disclosed. A transmitted signal processing circuit for receiving the audio signal and altering the audio characteristics provides the altered audio signal at the output of the signal processing circuit to the input of the two wire telephone system. A first line hybrid echo canceler is coupled to receive the output of the transmitted signal processing circuit and produce a plurality of first echo outputs in response to the transmitted signal processing circuit output and has a first error signal input. A first difference circuit has an input of first polarity and is coupled to the output of the input coupling circuit, and inputs of opposite polarity coupled to the echo outputs of the first line hybrid echo canceler.

Abstract: A speaker telephone comprising a microphone outputting an electrical signal, and a loudspeaker is disclosed. An amplifier has its output coupled to the loudspeaker. This amplifier has non-inverting and inverting inputs. A switch having two positions couples the microphone to the amplifier or couples the tuning signal source to one of the inputs of the amplifier. A tuning signal source and control circuit output a tuning signal. Initiation means initiates a tuning sequence by causing the switch to be in the second position and causing the tuning signal source and control circuit to generate tuning signals. A coupling device is connected to one of the inputs of the amplifier and adopted to be connected to a telephone circuit. A hybrid voltage generator circuit is responsive to the output of the microphone when the switch couples the microphone to the amplifier to generate at its output a cancellation signal which prevents transmitted voice signals from appearing at the loudspeaker.