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When a vehicle is in motion, noise is generated in the cabin that is composed of noise in multiple narrow-frequency bands and caused by input from the road surface. This type of noise is termed low-frequency-band road noise, and its reduction is sought in order to increase occupant comfort. The research discussed in this paper used feedback control technology as the basis for the development of an active noise control technology able to simultaneously reduce noise in multiple narrow-frequency bands. Methods of connecting multiple single-frequency adaptive notch filters, a type of adaptive filter, were investigated. Based on the results, a method of connecting multiple filters that would mitigate mutual interference caused by different controller transmission characteristics was proposed.

The conventional active noise control technology for engine booming noise1 based on the Filtered-Reference LMS algorithm 2,3 has a conflict in between the ability of tracking a change of engine rpm and simultaneously controlling the low frequency (low rpm) region. As a result, the conventional approach is difficult to apply for booming noise for a low rotation engine, an important region for weight reduction of a vehicle. Because of these reasons, there are few applications of the conventional approach to reduce booming noise. The purpose of this study is to propose a less complex ANC system based on a Single-frequency Adaptive Notch (SAN) 2,4 algorithm. The system proposed in this paper solves the problem of good control performance in the low rotation or rpm region, assures the stability related to a mass production, and reduces the number of component parts in a manufacturing process.