推挽式駐極體揚聲器之實驗建模與最佳化設計

Abstract

推挽式駐極體揚聲器是由輕、薄的駐極體材料製成的平面揚聲器，但低頻響應的不足是其缺點。因此，搭配動圈式重低音系統可以補償低頻響應的不足，組合成一套完整的音響系統。 本論文中利用電阻抗量測、曲線嵌合法以及質量增加法可以有效鑑別出低音揚聲器單體的T-S參數。利用T-S參數以及機電聲類比電路中，即可建立重低音揚聲器的集中參數模擬平台。藉由此平台可進行反射式音箱的設計模擬，搭配約束最佳化方法可對音箱尺寸做最佳化設計以提升低頻響應。 本論文亦對推挽式駐極體揚聲器進行分析與最佳化。本論文提出一個完全利用實驗法對駐極體揚聲器建模的技術與駐極體揚聲器的最佳化設計程序。因為駐極體揚聲器的電、機系統的耦合關係薄弱，因此傳統利用電阻抗量測來進行參數鑑別的方法並不完全適用於此揚聲器。因此，本論文發展了一套新的駐極體揚聲器實驗建模法，用來鑑別駐極體揚聲器的電聲參數。利用雷射速度量測儀量測揚聲器的振膜速度響應，進而鑑別出機械系統參數。搭配測試箱法，即可估測電-力轉換因子與運動阻抗特性。利用此實驗鑑別法建立的模型可以提供一個模擬平台，有效預測駐極體揚聲器的響應以及用於最佳化設計。利用模擬退火法可計算出在多目標函數與多拘束條件下的最佳化參數。不論對於多變數的廣泛求解或者只對於最佳間距的簡單求解都可以藉由模擬退火法來達成。結果顯示最佳化設計可以有效提升駐極體揚聲器的性能。

A push-pull electret loudspeaker is a flat type loudspeaker, and it is made with the thin and light electret material. The absence of low frequency response is a defect of the push-pull electret loudspeaker. Therefore, the subwoofer system is adopted to recover the low frequency response. The combination of the push-pull electret loudspeaker and the subwoofer can provide a complete audio system. Via the electrical impedance measurement, the curve fitting and added mass method, the T-S parameters of the subwoofer can be identified. The conventional lumped parameter model of the subwoofer can be established using the EMA analogous circuit and T-S parameters. Next, the conventional lumped parameter model is employed to the simulation of vented-box system. The constrained optimization technology was also employed to find the design that can enhance the low frequency response of the vented-box system. The push-pull electret loudspeaker is also analyzed in this thesis. A fully experimental modeling technique and a design optimization procedure are presented for push-pull electret loudspeakers. Conventional electrical impedance-based parameter identification methods are not completely applicable to electret speakers due to the extremely weak electromechanical coupling. This prompts the development of a new experimental technique for identifying the electroacoustic parameters of the electret speakers. Mechanical parameters are identified from the membrane velocity measured using a laser vibrometer. The voltage-force conversion factor and the motional impedance are estimated, with the aid of a test-box method. This experimentally identified model serves as the simulation platform for predicting the response of the electret loudspeaker and optimizing the design. Optimal parameters are calculated by using the simulated annealing (SA) algorithm to fulfill various design goals and constraints. Either the comprehensive search for various parameters or the simple search for the optimal gap distance can be conducted by this SA procedure. The results reveal that the optimized design has effectively enhanced the performance of the electret loudspeaker.