Abstract
One of the problems concerned with active noise control is the existence of acoustical feedback between the control value (“active” loudspeaker output) and the reference signal. Various experiments show that such feedback can seriously decrease effects of attenuation or even make the whole ANC system unstable. This paper presents a detailed analysis of one of possible approaches allowing to deal with acoustical feedback, namely, virtual unidirectional sound source. With this method, two loudspeakers are used together with control algorithm assuring that the combined behaviour of the pair makes virtual propagation of sound only in one direction. Two different designs are presented for the application of active noise control in an acoustic duct: analytical (leading to fixed controller) and adaptive. The algorithm effectiveness in simulations and real experiments for both solutions is showed, discussed, and compared.
Highlights
Active noise control is mainly concerned with low-frequency sounds that cannot be suppressed in passive manner at reasonable cost
The approach to acoustic feedback cancellation presented in this paper is called virtual unidirectional sound source (VUSS)
The idea of virtual unidirectional sound source (VUSS) is to use digital signal processing algorithm to drive two loudspeakers in such way that the sound produced by them propagates only downstream the duct [7]
Summary
Active noise control is mainly concerned with low-frequency sounds that cannot be suppressed in passive manner at reasonable cost. The best one that avoids acoustic feedback completely is to use nonacoustic reference sensor This usually limits the application to cancel the tonal sounds and does not allow for the reduction of broadband noise. Another approach to acoustic feedback is to internally process signal from the reference microphone in a way allowing to compensate for this effect [2, 4,5,6]. The approach to acoustic feedback cancellation presented in this paper is called virtual unidirectional sound source (VUSS). The method, in authors opinion, has some advantages over well-known two loudspeaker active noise control system in duct applications. Experiments of feedforward active noise control system using virtual unidirectional sound source
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