Performance of a multichannel active sound radiation control system near a reflecting surface

Prior research shows that introducing a reflecting surface near an active control system can improve its noise reduction performance; however the mechanism of the performance improvement is not completely clear. This paper investigates the effects of a reflecting surface on multichannel active sound radiation control systems with a primary monopole source located on the surface. By using a genetic searching algorithm, the locations of secondary sources were optimized to maximize the noise reduction and the frequency range that can be beneficial from the reflecting surface is discussed. It is found that the performance improvement by introducing a reflecting surface is due to the increased sound pressure generated by the secondary sources at the primary source location. The beneficial frequency range extends with the number of the channels of the control system and has an upper limit frequency determined by the distance between the secondary sources and the primary source. Experiments are conducted to validate the results.