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Adaptive Active Noise Control


C. Pahud

no. 8816, Term Project at the Automatic Control Lab, ETH Zürich, SS 98.

The main goal of this project was to reduce noise in a duct with an adaptive approach. This goal is reached. For both versions of the controller (with and without reference microphone) and for all studied physical configurations , the adaptive approach gives significant attenuation. The problem of the acoustic feedback between the compensator speaker and the reference microphone, which can cause instability, is quasi automatically solved by the adaptive controller itself. The adaptive algorithm used to update the coefficients of the adaptive filter is the LMS algorithm. This algorithm is simple to implement and does not require a lot of computation. It has been shown that the performance limitations are mainly due to the external noise, to the non-minimum phase zeros of the secondary and reference path and to the convergence rate of the LMS algorithm itself. The influence of the non-minimum phase zeros of the secondary and reference path can be improved by changing the configuration of the plant. For example, It was shown that large resonance frequency, due to poor damping in the duct, limit significantly the performance. The slow convergence rate of the controller is principally in a non-stationary environment. Hence, we can expect a low tracking capabilities of the LMS algorithm.

Further Information

Type of Publication:

(13)Semester/Bachelor Thesis

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% Autogenerated BibTeX entry
@PhdThesis { Xxx:1998:IFA_169
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