微型喇叭之輸出分析及品質改善之研究

Abstract

本研究的主要目的在於利用所建立的非線性喇叭分析模式，來推導回饋線性化控制理論的控制器，進而應用於實際喇叭的非線性輸出控制，期能降低高頻諧波的音量。 本文的研究分為兩部分，首先考慮喇叭運作的電路、薄膜振動與聲音輻射，分別建立線性化的方程式，並合併得到輸入電壓與薄膜振動位移以及輸出音壓間之關係，建立完整的喇叭模擬系統，並在離散域下模擬電壓輸入喇叭系統所產生的聲壓，藉此分析微型喇叭中各個部份對於頻率響應的影響，並透過實驗量測驗證模擬分析的正確性。 第二部份為探討微型喇叭系統內元件的非線性效應對於喇叭頻率響應的影響，首先模擬微型喇叭的非線性系統，並對喇叭在實際量測時所產生的非線性輸出加以討論，以實際量測結果作為依據，修正非線性模擬所需的電-力轉換係數。最後使用回饋線性化(Feedback Linearization)之理論來對喇叭系統做控制，建立一逆動態模型(Inverse Dynamic)來降低或消除其非線性效應，以使喇叭在較大聲壓輸出時仍可維持較好的聲音輸出品質。

An application of feedback linearization control for micro-loudspeakers is presented in this paper. With inverse dynamic processor, signal distortion caused by loudspeaker nonlinearities can be compensated. First of all, the loudspeaker system separates into three parts: electrical, mechanical and radiation to build the classical linear and nonlinear models. Then converting the theoretical model into discrete-time system and using digital processing technique to simulate the output of the loudspeaker system. The theoretical model is verified by comparing the frequency response of real loudspeaker to the numerical result of simulation. The agreement is good. The second part is to investigate the effect of the parameter variation on the output of the loudspeaker. In this study only the transduction coefficient varies with displacement is considered. This 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 cancel the harmonic signals effectively. Finally, the present approach is applied on the nonlinear control of the real loudspeaker. The result is some parts of harmonics are reduced obviously. But some output sound signal seems not be improved under control. This may due to the incorrect values of transduction coefficient. But it still needs a further study.