Fujii K., Yamaguchi K., Fujita Y., Muneyasu M.

This paper verifies the performance of the simultaneous equations method by using an experimental active noise control system. The 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, called secondary path filter, this method uses an auxiliary filter identifying the overall path consisting of a primary path, a noise control filter, the secondary path and a feedback path. As inferred 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. By solving the independent equations, the method estimates the coefficient vector of the noise control filter minimizing the output of the error microphone. In the estimation, the identification of the secondary path is unnecessary. This means that the method can automatically recovered the noise reduction effect degraded by path changes without refreshing the coefficients of the secondary path filter. This paper verifies the automatic recovering by using an experimental system, where a frequency domain adaptive algorithm is applied to the identification of the overall path. The processing cost thereby decreases and also the noise reduction speed increases. The experimental results giving the stable noise reduction effect of more than 30 dB show that the method successfully works in practical systems.