ALLEN ROGER DAVIDSON JR
Engineers in Bowie, MD

4025724, May 24, 1977

Aug 12, 1975

5/603978

Allen R. Davidson - Bowie MD
Timothy G. F. Robinson - Severna Park MD

Westinghouse Electric Corporation - Pittsburgh PA

H04B 1500

179 1P

An array of independent sound cancellation units is arranged over a vibrating noise generating surface. Each unit includes an arrangement of acoustic transducers (sensors) positioned adjacent the surface to obtain an electrical average of the local acoustic noise generated by a predetermined zone of the surface. The summed average is changed in phase and gain by an active filter whose output drives an acoustic projector also positioned adjacent the surface and the acoustic output of which sums with the original noise signal in the acoustic far field, thus tending to cancel the noise. In essence, each vibrating surface zone and its associated sound cancellation unit tend to form an acoustic doublet. A signal indicative of the projector output is used as a feedback signal, with appropriate time delays, to cancel the effect of the projected output signal being picked up by the unit's transducers, and to cancel the effect of the output of other projectors of the array.