Coherence-based performance analysis on noise reduction in multichannel active noise control systems

Abstract

Active noise control (ANC) over an extended spatial region using multiple microphones and multiple loudspeakershas become an important problem. The maximum noise reduction (NR) potential over the control area is a criticalevaluation variable as it indicates the fundamental limitation of a given ANC system. In this paper, a method tomathematically formulate the NR potential for any given multichannel ANC systems is developed. First, the residualerror in the multichannel feedforward ANC system is formulated, and then the multiple-input-multiple-outputproblem is decomposed into the parallel-channel problem. The total energy of the residual error is further decom-posed into three different terms representing (i) the signal coherence between the reference signals and error signals,(ii) the filter, and (iii) the system null space. The experimental results validate the proposed evaluation method andillustrate the effectiveness on the maximum NR performance evaluation for given systems. Using the proposed ana-lyzing method, more insight into the contribution of each component to the NR potential can be achieved