Patent ID: 6748087
Filing Date: 2004-06-08
Classification: G10K,H04R

Abstract:
A headset for active noise cancellation of unwanted environmental noise, comprising an earpiece adapted to be held against the ear, said earpiece comprising:an earpiece shell; a drive unit incorporated in the shell; a microphone incorporated in the shell to detect unwanted noise and feed via an inverting amplifier a phase inverted, unwanted noise cancellation signal to the drive unit; and a cushion carried by the earpiece shell; an electronics unit, said electronics unit completing a feedback loop which includes an inverting amplifier means adapted to generate an amplified, phase inverted signal from an unwanted noise signal received from the microphone and to feed said phase inverted signal to the drive unit, the acoustic gain of the feedback loop being increased when the earpiece cushion is compressed against the ear beyond a predetermined extent; characterised in that means are provided on the earpiece shell for restricting compression of the cushion against the ear to the extent necessary substantially to prevent acoustic gain increasing beyond a threshold which gives rise to the generation of sound oscillations at the earpiece, said compression limiting means being adapted to restrict compression of the cushion not to exceed said predetermined extent.