音箱設計對揚聲器暫態響應之影響分析

The effects of box design on the transient response of a loudspeaker

林昱豪(Yu-Hou Lin)

指導教授 ： 王昭男

國立臺灣大學/工學院/工程科學及海洋工程學研究所/碩士(2014年)

https://doi.org/10.6342/NTU.2014.02836

摘要

本研究主要為利用等效電路法模擬出揚聲器振膜的位移曲線，並利用短時傅立葉變換，將時域的位移曲線轉換至時頻域，並在時頻譜圖上，截取出共振頻率的能量隨時間衰減的衰減曲線，將以此曲線判斷揚聲器系統暫態響應的好壞。
本研究共分為兩部分。首先，利用等效電路法，把揚聲器系統簡化為電-機-聲等效電路，再利用此三個等效電路導出三組方程式，聯立求解並進而模擬出揚聲器系統的位移曲線。其次，利用Matlab軟體，將時域的位移曲線轉換至時頻域，並在時頻譜圖上，取出共振頻率的能量隨時間變化的資料點，再將這些資料點做曲線擬合(curve fitting)以求得衰減曲線，最後求出此曲線的時間常數來判斷系統的暫態響應，時間常數愈短，暫態響應愈好。第二個部分，將製作出揚聲器系統的實體，並利用本實驗室的設備量測出系統的位移曲線，再將此曲線的資料匯入Matlab做處理，最後求得時間常數，並與模擬結果做比較。
研究結果顯示，密閉式音箱的大小對揚聲器暫態響應沒有影響；開孔式音箱的管徑大小愈小，管徑長度愈短，暫態響應愈佳；六階音箱的外側管管徑愈小，暫態響應愈佳。本研究成果可作為改善揚聲器暫態響應的方針。

關鍵字

揚聲器系統 ； 機電聲等效電路法 ； 短時傅立葉變換 ； 揚聲器暫態響應

並列摘要

This thesis is used of equivalent circuit method to simulate the displacement curve of the loudspeaker diaphragm, then using short-time Fourier transform to make time domain displacement curve convert to the time-frequency domain. Then interception of the energy data on resonance frequency that decay with time and then plot the decay curve. Finally, this curve will determine the transient response of the loudspeaker system is good or bad.
This thesis consists of two parts. First, by equivalent circuit method, the loudspeaker system could be simplified to electro-mechano-acoustic analogous circuits, then using these three equivalent circuits to derive three equations. By solving these equations, the simulated displacement curve of the loudspeaker system could be calculated. Furthermore, time domain displacement was converted to time-frequency domain through Matlab software. Then the energy points on resonance frequency can be intercepted on the time-frequency spectrum. Finally, the time constant of the curve would be calculated to determine the performance of transient response. The shorter it is, the better transient response is. Second, produce a loudspeaker system by using Applied Acoustics’s equipment so that we could measure the displacement curve of the system, then the data processing would be imported by using Matlab software. Finally, Time constant would be compared with the simulation results.
The results showed that the size of the closed box does not affect the transient response of the loudspeaker. For vented-box loudspeaker system: the transient response must be enhanced if we reduced the diameter or length of the tube. For six-order loudspeaker system, the performance of transient response depended on diameter of outside tube, the shorter it is, the better transient response is. Finally, these results can be used as guidelines to improve the transient response of the loudspeaker.

並列關鍵字

loudspeaker system ； electro-mechano-acoustic analogous circuits ； short-time fourier transform ； transient response of the loudspeaker

參考文獻

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