Abstract: This invention is directed to a system for the active acoustic attenuation of noise produced in the interior of an enclosure by a source of noise which in one aspect comprises input sensing operable to sense the source noise to be attenuated, cancellor adapted to produce noise 180.degree. out of phase with the source noise and error sensor operable to sense the acoustic summation of the source noise and the noise produced by the cancellor. The input sensor, cancellor and error sensor are each preferably disposed at or immediately adjacent an area of high acoustic pressure within the enclosure. The system further includes a second input sensor disposed adjacent the source of noise, a second cancellor adapted to introduce noise 180.degree. out of phase with the source noise at a location at or immediately adjacent the enclosure wall and second error sensor disposed in the interior of the enclosure.

Abstract: A non-porous, sound-absorbing panel which can be readily cleaned and which is intended for use in high humidity, sanitary environments. The panel comprises two non-porous membranes or panels bonded to opposite sides of a honeycomb structure. At least one membrane is formed of sound-absorbing material with the membrane natural frequency, the membrane/honeycomb cavity natural frequency and the standing wave natural frequency of the honeycomb cavities being closely matched. In a preferred embodiment of the invention, the membrane comprises a polyurethane panel; while the honeycomb structure is formed from phenolic impregnated paper.