動圈式揚聲器非線性失真之控制研究

Abstract

本研究主要目的在於將回饋線性化控制理論的控制器應用於動圈式揚聲器的非線性輸出控制，得到降低其失真的效果。首先考慮揚聲器的電路、振膜振動與聲音輻射，分別建立線性化的方程式，推導得到輸入電壓與薄膜振動位移之關係，並建立完整的揚聲器模擬系統。本研究僅考慮揚聲器特性參數隨位移改變所造成之非線性效應，利用前述模擬系統方程式探討微型揚聲器特性參數的非線性效應對於揚聲器輸出的影響,並使用回饋線性化(Feedback Linearization)之理論來對揚聲器系統做控制，在訊號輸入揚聲器前先經過控制器，降低或消除輸出之非線性效應,使揚聲器在低頻較大聲壓輸出時仍可維持較好的聲音品質。在揚聲器模擬系統中，控制器大幅降低了輸出之非線性效應，可以證明此理論是有效的。最後透過實驗量測驗證模擬分析的正確性，由實驗結果可以證實回饋線性化控制器對於實體揚聲器輸出改善是有效果的，不論是單體或是密閉式揚聲器系統，控制後的THD在各個頻率皆有明顯的下降。

This paper focuses on the application of feedback linearization control for moving-coil loudspeaker to reduce the output distortion. Signal distortion caused by loudspeaker nonlinearities can be reduced with inverse dynamic processor. First of all, the loudspeaker system separates into three parts, i.e. electrical, mechanical and radiation components, to build the models. Then the system equations are used to investigate the effect of the nonlinear parameters on the output of the loudspeaker. The nonlinearity will cause unwanted harmonics in the response of loudspeaker. To reduce this nonlinear effect, a feedback linearization method from nonlinear control theory is applied to the nonlinear loudspeaker model. Numerical simulation reveals that the feedback linearization method can reduce the harmonic signals effectively. Finally, the present approach is applied on the nonlinear control of the real loudspeaker. The results show that the THD (total harmonic distortion) of the output response reduced significantly in the cases of loudspeaker and closed-box loudspeaker system.