Abstract
This study proposes a new method for feedforward‐type active noise control systems. This method, named the frequency domain simultaneous equations method, is based on a different principle from the filtered‐x algorithm requiring a filter modeled on a secondary path from a loudspeaker to an error microphone. Instead of the filter, this method uses an auxiliary filter identifying the overall path consisting of a primary path, a noise control filter, and the secondary path. As seen from the configuration of the overall path, the auxiliary filter can provide two independent equations when two different coefficient vectors are given to the noise control filter. In practical use, the two different coefficient vectors are provided by their own estimation errors. By solving the independent equations, the proposed method can estimate the coefficient vector of the noise control filter minimizing the output of the error microphone. This study first presents computer simulation results demonstrating that the proposed method can automatically recover the noise reduction that is in effect degraded by path changes. Finally, this study applies the proposed method to an experimental system and, by using the system, verifies that the proposed method is functional in practical systems.
Highlights
The filtered-x algorithm [1] is widely applied to the feedforward type of active noise control (ANC) system [2]
The essence of the difficulty in the repeated identification is that the feedforward type system involves two unknown paths: the secondary path and a primary path from a noise detection microphone to an error microphone
This paper has proposed the frequency domain simultaneous equations method capable of automatically recovering the noise reduction effect degraded by path changes
Summary
The filtered-x algorithm [1] is widely applied to the feedforward type of active noise control (ANC) system [2]. The algorithm requires a filter, called secondary path filter, exactly modelled on the secondary path from a loudspeaker to an error microphone, whereas the secondary path in practical systems is continuously changing. To identify the two paths under active noise control, a device for yielding another independent equation is requisite [4] As such a device, [5] presents a way of feeding an extra noise to the loudspeaker. By using the auxiliary filter, the method identifies the overall path from the noise detection microphone, through the primary path, the noise control filter and the secondary path, to the error microphone. The simultaneous equations method repeatedly updates the coefficient vector, and thereby automatically recovers the noise reduction effect degraded by path changes. This paper first presents a simulation result demonstrating that the proposed method gives much higher noise reduction speed than that of the filtered-x algorithm, and by using an experimental system, verifies the performance of the proposed method
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