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Fully adaptive active noise control dealing with changes of secondary path response

This paper is concerned with a general structure and adaptive algorithms for active noise control and their application to noise cancelling for an air duct. Adaptive control algorithms play an essential role in dealing with uncertainties and changes in primary and secondary path response dynamics of sound propagation. Two new adaptive approaches are proposed and investigated in this paper. One is a direct adaptive approach which gives a stability-guaranteed adaptive algorithm for updating a feedforward adaptive controller. Unlike the ordinary filtered x algorithms, the distinctive feature of the proposed algorithm is in its assurance of stability and boundedness based on the strictly positive real property of an error model. However, it requires that the secondary path response should be known a priori and be constant. The other is an indirect approach which gives a fully adaptive algorithm available in a case in which the both primary and secondary path responses are uncertain and changeable. The algorithm consists of identification of two transfer function models and calculation of the corresponding feedforward controller.