The study of an adaptively active control on the acoustic propagation in a pipe

This paper is on the use of an active noise control (ANC) system combined with an extended tube to greatly reduce downstream noise and to avoid the serious influence of acoustic feedback caused by the secondary source. In order to minimise the acoustic pollution, a more stable finite impulse response (FIR) filter than IIR filter is also selected for this study. Moreover, in order to minimize the cost function defined by error and control signals, an adaptive feedforward algorithm based on the method of steepest descent is used to reduce the contradictory situation of reducing the residual noise and avoiding too high a control signal. rn addition, a modified LMS algorithm with an inverse impulse response function of error plant is used to diminish the unsteady influence resulting from the estimation error of error plant. Finally, a real-time ANC system is set up to verify the required performance of noise reduction for this study. The result clearly shows that the adopted ANC system can reduce a dual-tone noise by 45 dB and a bandlimited noise by 20 dB. (C) 1998 Elsevier Science Ltd. All rights reserved.