An adaptive controller for the active absorption of sound

Orduna-Bustamantea, F. and Nelson, P. A. (1992) An adaptive controller for the active absorption of sound. Journal of the Acoustical Society of America, 91 (5), 2740-2747. (doi:10.1121/1.403779).

Record type: Article

Abstract

An adaptive system is presented that allows a secondary acoustic source to become an active absorber of sound at the end of a closed duct. The system can also be generalized in order to achieve other termination impedances. The system consists of a loudspeaker, two microphones, and signal processing hardware including a digital signal microprocessor. The signals from the microphones are processed to obtain an error signal that represents the difference between the actual and the desired acoustic impedance of the termination. An absorbing termination requires, for example, that the microphone pair acts as a unidirectional probe picking up the sound reflected from the active termination only. This signal is used as the error signal that the digital controller is required to minimize. A simple analysis shows that this can be done adaptively using the “filtered-X” LMS algorithm. A simple experimental setup is used to obtain an absorbing termination which is shown to work with periodic, random, and transient input signals.

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