臺灣大學: 工程科學及海洋工程學研究所陳國在康家瑋Kang, Jia-WeiJia-WeiKang2013-03-272018-06-282013-03-272018-06-282010http://ntur.lib.ntu.edu.tw//handle/246246/252545本論文利用共振腔被動式消音原理結合適應性主動控制方法，對管道中低頻聲音進行消音效果探討。本文利用FIR(Finite Impulse Response)數位濾波器，來作為本論文之控制系統的主體架構，並以LMS(Least Mean Square )演算法來即時修正數位濾波器之係數，以求得最佳的控制效果。 在適應性主動控制實驗方面，本論文之主要噪音源以及LMS控制器的參考訊號，均由訊號產生器直接提供，以單純化控制系統，進而研討共振腔消音能力與揚聲器之關係，達到消音目的，故可不須考慮第二音源所產生的回饋聲場。 本論文之研究結果顯示，共振腔針對共振頻率中心有近30dB的消音效果，且頻寬可達50Hz，而傳統揚聲器聲源針對單頻的聲音，在管道下游其聲音強度皆可達約30~50dB的消音效果，而對於訊號產生器發出共振頻率與另一低於1000Hz的雙頻訊號，共振腔仍對共振頻率亦有約30dB的消音效果，而揚聲器也保有一定效能，第二聲源之揚聲器與霍姆赫茲共振器可同時存在於一裝置中。最後本論文亦討論此方式輔助適應性主動控制消音，於寬頻與雙頻效果之優劣。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.5078834 bytesapplication/pdfen-US管道聲場消音性能適應性演算法Acoustic Fieldsin Ducthttp://ntur.lib.ntu.edu.tw/bitstream/246246/252545/1/ntu-98-R97525061-1.pdf