| Summary: | 碩士 === 臺灣大學 === 工程科學及海洋工程學研究所 === 98 === There are two techniques in noise control, which are passive and active noise controls. This study is to provide a new approach, of which a conventionally used loudspeaker is combined with a resonator, to active noise control (ANC).
Speaking to the compound sources as used, the acoustic waves produced by the controllable loudspeaker in the resonator can reduce its downstream sound pressure greatly at the resonant frequency of the resonator, which is generated from the primary noise sources. Impressively, the two techniques as used don’t interfere negatively to each other.
Regarding to the experiment, it is to use a FIR digital filter as the main structure of the involved, and meanwhile to directly take single- or dual- frequency signal from function generator as the reference input. To achieve the best active control performance, the weighting coefficients of the digital filter are adjusted by using an appropriate LMS algorithm.
The results of this study show adding a conventional loudspeaker in a resonator can provide attenuation of downstream pressure level by almost 40 dB below 1000 Hz. Otherwise, use of a single Helmholtz resonator can provide an attenuation of downstream pressure level by about 30 dB at its resonant frequency.
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