臺灣博碩士論文加值系統

　　噪音已是現代生活上逐漸受到重視的問題。而一般噪音之降低所使用的方法，對於高頻噪音的消除較為有效。對於低頻噪音的抑制相對地困難度較高而效果有限。因此，本研究針對500Hz以下的低頻噪音，利用主動控制的概念，以外加的聲源，即時產生一組與噪音振幅大小相同、相位相差180°的反相噪音，以進行干涉抵消低頻噪音源，而達到抑制之效果。
　　研究針對變電所之風機所產生之低頻噪音，以LMS與FxLMS兩種適應演算法來設計控制器。在系統實體測試之前，先利用MATLAB軟體來模擬適應性控制器的可行性，作為控制器設計之依據。實作的部份，為了避免電腦運算速度不足而影響噪音抑制的效能，故採用商業專用的數位信號處理器，作為控制器的核心。以CCS軟體撰寫控制程式與外部擷取程式，使外部訊號可由麥克風量測後，送入控制器做處理。研究過程可分為三個階段：第一階段改變反噪音源的入射方向，找出最佳的配置；第二階段則比較單通道及雙通道控制器之消音能力；第三階段以不同演算法來設計控制系統，並導入實際風機噪音進行測試。
　　研究結果顯示，反噪音源在各種不同的配置下，對於單頻噪音之平均消音量皆達到4dB以上的效果。此外，若將系統改為多通道控制結構，則對單頻噪音之平均消音量可提升至7dB以上，而多頻噪音抑制的部份，平均消音量也都有4dB以上的效果。比較起來，噪音抑制的能力明顯比單通道控制系統好。另外，採用FxLMS演算法來實現控制系統，並導入實際變電所噪音進行抑制，結果可得到約10dB左右的消音效果，證明本實驗所設計之主動控制系統，具有抑制真實噪音的能力。

　　The noise around our living environment is always a troublesome problem for our daily life. The traditional methods in reducing noise are mostly using the sound-absorbing materials to block the transmission of noise. These methods are good for the high-frequency noise and are less effective for the low-frequency noise. It is then set as the target of this study to suppress the noise with frequencies lower than 500Hz. The concept of active control is adopted to generate a set of noise-suppressing sound source which has the same amplitude but opposite phase to that of the low-frequency noise.

　　The study applies two kinds of adaptive algorithm of the LMS and the FxLMS to design the controller in restraining the typical low-frequency noise from the blower of the transformer station of the electricity supply system. Before the physical testing of the system, the MATLAB software is used to simulate the feasibility of the adaptive controller with the simulated results as the basis for the design of the controller. Besides, a commercial digital signal processor is adopted as the core of the signal controller. It is anticipated that its calculating speed will be fast enough to avoid the performance degrading of the noise control system from using the general personal computer of which with much slower processing speed. For the control software design, both the control program and the data acquisition program are written in CCS software and the external signals measured with microphones are then processed with the controller. Generally, the study processes can be divided into three stages: the first stage is to find out the best locations and input directions of the anti-noise source; the second stage is to compare the noise elimination capability of the single-channel controller with that of the multi-channel controller; the third stage is to use different algorithm for the design of the control system and to use the field test noise of the blower to check the performance of the controller.

　　The results show that with different installation locations of the anti-noise source, it can reduce more than 4dB for the single-frequency noise. A step further by changing the system into a multi-channel control system, it can reduce about 7dB averagely for the signal frequency noise. Furthermore, the multi-channel active noise control system can also reduce more than 4dB for the broadband noise. It indicates that the multi-channel control system is more effective then the single-channel control system. When applying the FxLMS algorithm for the design the controller and taking the field test noise of the blower as input to the control system, it is found that about 10dB of the noise is suppressed. Through all these test results, it is believed that the designed active control system is effective for the suppression of low-frequency noise.

中文摘要............................................................................Ⅰ
英文摘要...................................................................................Ⅱ
誌謝.........................................................................................Ⅳ
目錄........................................................................................Ⅴ
表目錄.........................................................................................Ⅸ
圖目錄.........................................................................................Ⅹ
符號說明....................................................................................ⅩⅣ
一、 緒論.................................................................................................1
1.1 簡介.................................................................................................1
1.2 研究目的與方法.............................................................................4
1.3 文獻回顧.........................................................................................6
1.4 論文架構.........................................................................................7
二、 噪音工程.........................................................................................9
2.1 聲學簡介.........................................................................................9
2.1.1 聲波.........................................................................................9
2.1.2 聲速.......................................................................................10
2.1.3 聲壓位準與聲功率位準.......................................................11
2.1.4 管路截止頻率.......................................................................12
2.1.5 消音性能評估.......................................................................12
2.2 被動式噪音控制簡介...................................................................14
2.3 主動式噪音控制簡介...................................................................16
2.4 噪音的定義與主動控制相關問題...............................................18
2.4.1 噪音的定義...........................................................................18
2.4.2 主動控制相關問題...............................................................18
2.5 環境噪音量測與法規...................................................................20
三、 控制理論與控制器設計...............................................................22
3.1 簡介...............................................................................................22
3.2 控制演算法...................................................................................24
3.2.1 適應性濾波器原理...............................................................24
3.2.2 LMS演算法..........................................................................27
3.2.3 第二路徑系統鑑別...............................................................28
3.2.4 FxLMS演算法......................................................................29
3.2.5 多通道(Multi-channel)之FxLMS演算法............................32
3.3 ANC控制系統分析與設計..........................................................35
3.3.1 前饋控制架構.......................................................................35
3.3.2 回饋控制架構.......................................................................36
3.3.3 混合控制架構.......................................................................37
四、 實驗架設.......................................................................................39
4.1 設備簡介.......................................................................................39
4.1.1 一維管的建構試驗...............................................................40
4.1.2 麥克風...................................................................................42
4.1.3 前置放大器(Preamplifier)....................................................43
4.1.4 訊號處理放大器...................................................................43
4.1.5 揚聲器...................................................................................44
4.1.6 功率放大器...........................................................................44
4.1.7 數位訊號處理器(DSP).........................................................45
4.1.8 頻譜分析儀...........................................................................46
4.2 實驗流程.......................................................................................47
五、 系統模擬.......................................................................................50
5.1 不同參數之消音性能比較...........................................................50
5.2 不同演算法之消音性能比較.......................................................57
5.3 不同噪音源之消音性能比較.......................................................60
六、 系統實體測試...............................................................................64
6.1 控制系統.......................................................................................64
6.2 反噪音源於不同入射方向下之消音性能比較...........................64
6.3 單通道與多通道控制系統之消音性能比較...............................72
6.4 不同演算法之消音性能比較.......................................................77
七、 結論與未來研究...........................................................................82
7.1 結論...............................................................................................82
7.2 未來研究.......................................................................................84
參考文獻........................................................................................85

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