ACTIVE SUPPRESSION OF SOUND DIFFRACTED BY A BARRIER - AN OUTDOOR EXPERIMENT

The active control method was used to suppress the sound diffracted by an outdoor barrier, This method operated by the cancellation of the s ound pressure at the diffraction edge of the barrier, which normally b ehaves like the virtual source of the diffracted field, The results of two experiments are shown in this paper. In the first experiment, we employed two independent controllers that utilized multi-channel adapt ive signal processing to minimize the sum of the mean square of the so und pressure at four and six points along the diffraction edge. Measur ement of sound pressure levels at various distances from the barrier s howed effective sound suppression, with about 6-dB excess attenuation over the barrier's insertion loss at the receiver at a distance of 50 m. A practically realistic noise source, a fan blower, was used as a p rimary source in the second experiment and the moderate attenuation co uld be achieved at almost all the receiver points. The results obtaine d in these two experiments provided the experimental verification of t he strategy for the active suppression of sound diffracted by a noise barrier. (C) 1997 Acoustical Society of America.