一般而言，使用主動式的方法來降低較低頻的噪音比較有效益。而主動式噪音控制系統的效能，取決於是否能先補償第二路徑的影響，進而產生與原噪音波形大小幾乎相同、相位幾乎相反的反噪音波形，利用破壞性干涉的原理來降低噪音。在本論文中，先介紹如何使用離線式適應性系統確認法及房間轉移函數這兩種方法來估測第二路徑，並搭配多通道Filter-X LMS演算法，最後使用前授控制系統來消除單頻弦波噪音。
然而，在某些情況之下，使用主動式噪音消除系統時，我們發現只有在誤差麥克風附近才有消音效果。換言之，只有把誤差麥克風放在距離人很接近的位置，才會感到噪音變小，這樣會造成使用上的不便。有鑑於此，我們提出了虛擬麥克風來解決這項困擾。使用虛擬麥克風的方法，在增加誤差麥克風與人的距離之情況下，仍可讓人感到噪音變小。在本論文中將深入探討虛擬麥克風的原理及實作結果。

In general, it is effective to use Active Noise Control (ANC) to reduce low frequency noise. ANC uses the destructive interference to reduce the noise, so that the performance of the system mainly depends on the anti-noise. Because the effect of secondary path would influence the precision of anti-noise, we discuss the methods of off-line adaptive system identification and Room Transfer Function (RTF) to model secondary path. Finally, using the multi-channel Filter-X LMS algorithm and feedforward system reduces the noise with single frequency.
However, ANC only reduces noise level around the error microphones in some conditions, but it is inconvenient that error microphones are close to us. Hence, we proposed a new method, virtual microphone, to overcome this problem. In using virtual microphone circumstances, we can still feel noise reduced as increasing the distance between people and error microphone. In this thesis, we discuss the theory of virtual microphone and experimental results.

目次
中文摘要……………………………………………………………………………...iii
英文摘要……………………………………………………………………………...iv
誌謝…………………………………………………………………………………....v
圖目錄………………………………………………………………………………...ix
表目錄………………………………………………………………………………...xi
第一章緒論…………………………………………………………………………1
1.1 研究動機…………………………………………………………………….1
1.2 各章內容介紹……………………………………………………………….3
第二章 理論基礎……………………………………………………………………4
2.1 簡介………………………………………………………………………….4
2.2 適應性濾波器的基本原理………………………………………………….4
2.2.1 均方誤差法…………………………………………………………6
2.2.2 最陡下降法…………………………………………………………8
2.3 最小均方演算法………………………………………….…………………9
2.4 Filter-X 最小均方演算法…………………………………………………12
2.5 前授控制系統…………………………….………………………………..15
第三章 使用房間轉移函數模擬第二路徑………………………………………..16
3.1 簡介………………………………………………………………………...16
3.2 房間脈衝響應的求法……………………………………………………...16
3.2.1 最大長度序列的產生……………………………………………..16
3.2.2 互相關運算的介紹………………………………………………..18
3.2.3 Fast Hadamard Transform…………………………………………20
3.3 模擬房間轉移函數的方法………………………………………………...21
3.3.1 使用全零點模組來模擬房間轉移函數…………………………..21
3.3.2 使用極/零點模組來模擬房間轉移函數………………………….22
3.3.3 使用共極/零點模組來模擬房間轉移函數……………………….23
3.3.4 共同極點的分析…………………………………………………..24
3.4 房間轉移函數的應用……………………………………………………...25
第四章 麥克風不在安靜區的理論探討及實現…………………………………..27
4.1 簡介………………………………………………………………………...27
4.2 多通道FXLMS演算法……………………………………………………27
4.2.1 使用適應性系統確認法估測第二路徑…………………………..27
4.2.2 使用共極/零點模組法估測第二路徑…...………………………..29
4.2.3 多通道前授式主動噪音消除系統………………………………..31
4.3虛擬麥克風的原理………………………………………………………...32
第五章實驗結果……………………………………………………………...….34
5.1簡介………………………………………………………………………...34
5.2實驗器材及空間配置圖………………………………………………...…34
5.2.1 實驗器材……………………………………………………...……34
5.2.2 空間配置圖………………………………………………………...35
5.3 使用離線式系統確認法估測第二路徑的實驗結果……………………...36
5.3.1 特定位置噪音消除的實驗結果…………………………………..36
5.3.2 安靜區範圍的描述………………………………………………..41
5.4 使用共極/零點模組模擬第二路徑的實驗結果……………..…………...51
第六章結論與未來展望………………………………………..………………..54
5.1 結論………………………………………………………………………...54
5.2 未來的展望………………………………………………………………...54
參考文獻………………………………………………………………………….….55

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