A near-field error sensing strategy for compact multi-channel active sound radiation control in free field

Noise reduction performance of a compact active sound radiation control system is significantly affected by locations of the error microphones which are required to be installed near the primary source. In this paper, near-field error sensing for multi-channel active radiation control systems in free field is investigated, and it is found that the optimal locations of error sensors for minimizing the sum of squared sound pressure are between the primary source and the secondary sources distributed uniformly on a sphere surface surrounding the primary source. Both simulation and experiment results show that the optimal locations of error microphones are independent of the type of primary source when there are sufficient secondary sources. These optimal locations remain unchanged at low frequencies and move toward secondary sources when the secondary source number increases. Therefore, for active radiation control applications in low frequency range, a compact multi-channel system can be developed by locating error microphones between the primary source and secondary sources.