Patent US 5,526,421

A voice transmission system including a microphone (13) in combination with active sound cancellation means comprising a speaker (14) and a signal processor (17) for generating a mirror-image waveform with respect to the signal generated when speaking into the microphone. The mirror-image waveform is used to activate the speaker (14) thereby cancelling the user's voice. This provides the user with complete privacy, since the cancellation prevents the user's voice from being overheard by others, even in a crowded area.