噪音的控制方法可分為被動式及主動式兩種,傳統上以被動式阻尼的技術或重新設計系統去消除中高頻率範圍的噪音,以主動式的方法去對低頻的噪音作控制。本文就玻璃平板面積大小不同之特性,以主動式的方法同時對低頻及高頻的噪音作控制,並比較其結果。 本文以前饋式FIR(Finite Impluse Response)數位濾波器及LMS(Least Mean Square)演算法作為控制系統之主要架構,並在實驗架構上分為兩種。第一種架構針對單頻率噪音,以單片陶瓷壓電材料分別去對大小面積的玻璃平板作主動控制。第二種架構針對雙頻率噪音,誤差輸入部分改以兩台濾波器以濾除高低頻雜訊,並同時激振兩塊壓電片以對雙頻噪音作消除。 實驗結果顯示,不論單頻或雙頻率噪音,在共振頻率下幾乎皆能達到10dB以上的音壓衰減量。另外,在非共振頻率下也有4dB以上的控制效果。
Noise control methods mainly have two techniques, which are passive and active noise controls. Traditionally we use passive damping techniques or redesign system to eliminate the medium and high frequency range of noise. This study use the characteristics of different size area to execute active noise control for both low and high frequency,and then compare the results. This study uses FIR digital filter and LMS algorithm as the main structure of the control system, and there are two frameworks for the experiment in this study. The first one involved for single-frequency noise use ceramic PZT to execute active control on area of different size plate respectively. The second part involved for dual-frequency noise change the hardware section to two filters to filter out the error input noise and excite two PZT at the same time. The result shows that for single or dual-frequency noise, it can attenuate almost more than 10dB at the resonant frequency. In addition, it can also achieve more than 4dB sound pressure attenuation at non-resonant frequency.
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