Evaluation of acoustic feedback cancellation methods with multiple feedback paths

Acoustic feedback limits the maximum stable gain of a public address system and may cause the system to become unstable. Acoustic feedback cancellation methods use an adaptive filter to identify the impulse response of the acoustic feedback path and then remove its influence from the system. However, if the traditional adaptive filtering algorithms are used, a bias is introduced in the estimate of the acoustic feedback path obtained by the adaptive filter. Several methods have been proposed to overcome the bias problem but they are generally evaluated considering a public address system with only one microphone and one loudspeaker. This work evaluates some of the state-of-art methods considering a public address system with one microphone and four loudspeakers that results in multiple feedback paths and corresponds to a more realistic scenario of a typical system. Simulation results demonstrated that, with multiple feedback paths, the acoustic feedback cancellation methods are able to increase in 12 dB the maximum stable gain of the public address system when the source signal is speech.