Adaptive Design of a Unidirectional Source in a Duct

Vesa Välimäki1 and Seppo Uosukainen2

1 Helsinki University of Technology, Laboratory of Acoustics and Audio Signal Processing, P.O. Box 3000, FIN-02015 HUT, Espoo, Finland

2 VTT Building Technology, Acoustics, P.O. Box 1804, FIN-02044 VTT, Espoo, Finland

ABSTRACT

An adaptive signal processing technique for the design of a unidirectional source for duct-acoustic applications is introduced. The source consists of multiple actuators. In this paper, two-element sources are considered. Directivity of the source is obtained by filtering the input signal of each actuator in an appropriate manner. The proposed adaptive system designs these filters automatically. One advantage of the approach is that the delay between the actuators---which is one of the main design parameters---need not be measured separately, since the system automatically learns the delay as part of the adaptation process. In addition, it becomes unnecessary to equalize the frequency responses of the actuators, since the adaptive system also accounts for this problem. Simulated examples demonstrate the effectiveness of the approach. The proposed technique may be used in an active noise control system for ventilation ducts, for example.

Keywords: active noise control, acoustic tube, acoustic waveguide, adaptive filter, audio signal processing, digital filter design, sound transmission, unidirectional actuator

This paper was published in the Proceedings of ISMA23---Int. Conf. Noise and Vibration Engineering, vol. 3, pp. 1253-1260, Leuven, Belgium, Sept. 16-18, 1998.

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Last modified: October 19, 1998
Author: Vesa Välimäki