A study of an actively controlled noise barrier

This paper describes an application of active control of sound diffracted by a barrier. The basis of this application is the cancellation of the sound pressure at the diffraction edge, which behaves like a virtual source to the diffracted field. Several points on the edge were canceled simultaneously by several secondary sources to get a large attenuation over a wide area. While many factors appear to influence the effectiveness of active control, the points of cancellation on the diffraction edge and the arrangement of the secondary sources were studied. The optimum conditions for control were investigated using numerical simulation. These conditions were then confirmed experimentally using multichannel adaptive signal processing. It was found that control is stable and effective when the intervals of the points of cancellation on the edge are shorter than half of the wavelength, and that attenuation is greatest when the secondary sources are nearest the primary source.