臺灣博碩士論文加值系統

揚聲器的非線性行為一直以來是電聲領域相當重要的課題，揚聲器在大振幅情況下的非線性行為包含了磁力耦合因子、剛性、電感隨音圈位移的非線性行為，而這也是造成失真的主要因子。以往開發揚聲器時只能透過錯誤嘗試法(Trial & Error Method)，不僅開發時間冗長且研發成本過高。因此本文利用有限元素模擬揚聲器之主要的失真參數，包含磁力耦合因子Bl(x) 、電感Le(x)及振膜剛性Km(x)，並利用KLIPPEL 量測系統驗證Bl(x)、Le(x)及Km(x)模擬的準確性，並嘗試搭配參數樣線法來求解揚聲器頻率響應特性及失真，建立一套揚聲器特性預測及診斷流程。
揚聲器非線性參數的設計應盡量設計為對稱的形式，能有效的降低諧波失真，但實際上由於揚聲器幾何的不對稱，造成揚聲器要設計出對稱剛性非線性特性較困難。因此本文提出透過調整音圈初始位置來優化不對稱的剛性非線性特性所引發之諧波失真。預期結果與實際成品量測之結果亦相當吻合，其總諧波失真降低約10%且同時也優化互調失真，顯示本文所建構的方法確實能作為一個有效改善揚聲器失真的方法。

The nonlinear effect of a moving-coil loudspeaker, originating from its magnetic coupling factor and the system’s stiffness, presents a significant impact on the sound quality. For improving the sound quality, this article proposes an approach to reduce the total harmonic distortion (THD) by adjusting the initial position of its voice-coil. First, a mathematical model involving the nonlinearities of force factor, mechanical stiffness, and inductance of voice coil is constructed and then solved using a novel algorithm called the parameter spline difference method (PSD). In the course of pursuing reduction of the corresponding THD of a typical moving-coil loudspeaker, the model was used to analyze the nonlinearity of the THD, revealing itself as a nonlinear function of force factor, the system’s stiffness and inductance of voice coil. For various initial positions of the voice-coil, the coupled nonlinear differential equations were solved using the PSD to yield corresponding sound pressure level and THD. To our satisfaction, the loudspeaker driver with its voice-coil optimally tuned for the initial position turns out to have a THD reduction of 10%, which is also consistent with our experimental observations.

第一章 緒論 1
1-1 研究背景 1
1-2 研究動機 2
1-3 文獻回顧 3
1-4 文章架構 6
第二章 非線性數學模式 8
2-1 揚聲器的非線性分析模型 9
2-2 RUNGE-KUTTA METHOD 13
2-3 參數樣線差分法(PARAMETER SPLINE DIFFERENCE METHOD) 15
2-4 數值方法之比較 18
2-4.1 線性的情況 19
2-4.2 非線性的情況 22
第三章 揚聲器固有的非線性特性評估 25
3-1 揚聲器磁力耦合因子(FORCE FACTOR)非線性行為評估 26
3-1.1 磁力耦合因子的模擬與驗證 27
3-2揚聲器電感(INDUCTANCE)非線性行為評估 33
3-2.1 電感非線性特性的模擬與驗證 35
3-3 揚聲器剛性(STIFFNESS)非線性行為評估 41
3-3.1 剛性非線性特性之模擬與驗證 43
第四章 功率定義及失真優化探討 47
4-1 揚聲器溫升分析模型及功率級探討 47
4-1.1 揚聲器溫升線性模型 48
4-1.2 揚聲器非線性熱模型 53
4-1.3 功率壓縮 (POWER COMPRESSION) 59
4-1.4 功率的預測 60
4-2 非線性行為的產物 66
4-2.1 直流偏移(DC DISPLACEMENT) 66
4-2.2 頻率響應特性動態壓縮(SENSITIVITY COMPRESSION) 70
4-3失真的優化 72
4-3.1 音圈初始位置與失真的關係 72
4-3.2實際成品驗證 82
第五章 結論與未來展望 88
5-1 結論 88
5-2 未來研究方向 89
參考文獻 93

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