Coherence between error and acoustic reference microphones with two closely located noise sources

It is well known that locating acoustic reference microphones near the error microphone can improve the coherence between reference and error signals in feedforward active noise control systems. In this paper, the effects of the number of reference microphones and the distance between noise sources and reference microphones on the coherence between the reference and error signals are investigated based on an analytical model. Two scenarios when the two noise sources are located on the same side or opposite sides of the error microphone are studied. The simulation results show that the coherence coefficient can reach 1.0 regardless of the distance between the noise sources and the reference microphones if the number of reference microphones is the same as that of the noise sources. When the number of reference microphones is less than that of noise sources, the coherence coefficient in the low frequency range decreases as the reference microphones move close to the noise sources.