動圈式揚聲器系統之無感測器重低音強健控制設計

Abstract

一般而言，動圈式喇叭揚聲器（moving -coil loudspeaker )之低頻響應通常不佳。究其原因，主要在於極低頻範圍內，揚聲器之薄膜（diaphragm）無法產生足夠之位移，進而產生足夠之體積速度（volume velocity）。本研究之動機在於利用現代控制理論之技巧，突破揚聲器原機電系統之限制，嘗試在低頻範圍對揚聲器的頻率影響作補償。有別於一般音響等化器（equalizer) 只對大小（magnitude）作補償，本研究嘗試同時對大小及相位（phase）進行最佳的補償。本系統以自我感測速度觀測器（self-sensing velocity observer）產生出速度參考訊號的提供控制器。而控制器的設計理論是基於前饋及回饋架構、H∞強健控制理論、有限長度預知控制（preview control）、H2模式匹配及適應控制，共設計五組，並以混合數位處理器（Digital Signal Processor, DSP）及頻比電路實現控制器。

In general, moving -coil loudspeakers have poor response in low frequency range. The main reason is due to the fact that the speaker diaphragm fails to produce sufficient volume velocity in low frequencies. To alleviate the problem, this study focuses on enhancing the low-frequency performance, given the electromechanical constraints of the original system, by means of modern control techniques. It is attempted that not only the magnitude but the phase of the frequency response are optimally compensatd. The proposed system does not require a sensor, whereas a self-sensing velocity observer is utilized for producing the cone velocity signal required by the controller. Feedback structurd and feedforward structure are employed to simultaneously achieve robust stabilization and tracking performance. The feedback controller is designed using H∞ robust control synthesis. The feedforward controller is designed on the basis of finite-length preview, H2 model matching principle, and adaptive control, respectively. The proposed controller is implemented and validated by using a combined digital signal processor (DSP)platform and operational amplifier (OP) circuits.