- 學位論文
結合可控制式平板與揚聲器聲源之管道聲場主動控制
Active Control on the Acoustic Fields in Duct by combing the Controllable Plate Source with Loudspeaker Source
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摘要
噪音防制方法主要可分為被動式噪音控制及主動式噪音控制兩種。實驗控制系統的主體架構採用有限脈衝響應(FIR)數位濾波器，參考輸入訊號由訊號產生器產生單頻或雙頻訊號提供，以最小均方(LMS)演算法來修正權重係數，達到主動式噪音控制的目的。 本論文將圓形管道的單一控制聲源改為兩個控制聲源，並將其中一個控制聲源由傳統喇叭換成方型薄板，並在平板中心貼壓電片，給予外力使其激振，結合傳統喇叭做主動控制，探討控制前後管道下游聲音位準的衰減量。 在實驗結果方面，在單頻部分，控制聲源為喇叭與平板時，在各個頻率管道下游聲壓位準衰減量比單一使用喇叭時多了約5dB~20dB，比單一使用平板多降了約5dB~35dB；而在雙頻部分，高頻的聲壓位準衰減量比單一使用喇叭時多降了約10dB，證明了平板聲輻射與喇叭聲輻射結合在管道主動噪音控制的可行性。
並列摘要
The noise control can be divided into two methods including active and passive noise controls methods techniques.The passive control is used to reduce the acoustic fields at medium and higher frequencies,and the active control is used to reduce those one at low frequencies. In this thesis,it is to combine the controllable rectangular plate source and the controllable loudspeaker source for the Active Control of sound(ANC).A rectangular plate and the loudspeaker used as the secondary source for active noise control in a circular duct are developed. Between them,the rectangular plate is fixed on a steel frame vertically and excited by a PZT which is attached to the middle of plate.The rectangular plate is simple in geometry,light mass,easily to construct and only a modification on the materials already installed on duct is required little. We use FIR digital filter as the main structure of the control system in this experiment and take a single-frequency signal directly from a function generator as the reference input.Coefficients of the digital filter are adjusted by using a LMS algorithm in order to achieve the best performance. From the result of the experiment in this study,when the controllable sources are the rectangular plate and the loudspeaker,a locally maximum attenuation of sound pressure levels by 60 dB is reached,which proves that using the combination of a plate source with and the loudspeaker to adaptively active control of sound field in a circular duct is feasible.
參考文獻
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