APPARATUS AND METHOD FOR GLOBAL NOISE REDUCTION

Apparatus is disclosed for attenuating sound radiated from a vibrating surface into a control volume as comprised of a source of a control signal indicative of the amplitude and frequency content of the sound transmitted from the vibrating surface. An actuator(s) or shaker is directly connected to the vibrating surface for further vibrating the vibrating surface to induce a cancelling sound into the control volume for combining with and attenuating the transmitted sound. A sensor(s) is also disposed within the control volume for detecting the resultant sound indicative of the combination of the cancelling and the transmitted sound to provide an error signal indicative thereof. A controller in the illustrative form of a computer executing a minimization algorithm, is responsive to the error signal for adaptively modifying the control signal as to phase and amplitude, which modified signal is applied to drive the actuator(s), whereby the error signal is driven to a minimum level and the sound within the control volume is similarly attenuated. One illustrative embodiment of this invention is particularly adapted to attenuate sound within the fuselage of an aircraft, wherein the principle source of noise is derived from the aircraft's engine and propeller and is introduced through the aircraft's fuselage into the aircraft's cabin. The actuator is coupled directly to the fuselage and is energized with the control signal adaptively modified as to phase and amplitude such that the cancelling sound emanating from the actuator(s) combines with and attenuates the engine and propeller noise within the aircraft cabin.