應用力學方法探討含音箱平面揚聲器之聲傳行為

Abstract

本文研究如何利用機械振動方式模擬含音箱平面揚聲器聲傳行為。在過去，音箱大部分是以等效電路方式分析，此種方法的缺點為與實際物理意義較無直接的關聯性，為了彌補此種方法缺點，本文建立振動模型研究音箱系統的振動行為，利用瑞利第一積分法(Rayleigh’s first integral)分析音箱系統的聲傳行為。本文的理論分析與實驗架設主要針對低音回復型音箱。在低頻的音箱聲傳行為研究，建立雙自由度振動系統分析；在中高頻部分建立一個含障板的揚聲器利用瑞利第一積分法 (Rayleigh’s first integral)計算系統聲壓。接著探討音箱體積、音管長度與音管孔徑對音箱系統整體聲傳之影響，最後建立低音回復式音箱設計準則。

This thesis investigates how to simulate the sound radiation of flat speaker with enclosure via a mechanical approach. In the past, the electrical circuit method has been widely used to analyze the sound radiation of a speaker system with enclosure. The shortcoming of this approach is that there's no direct relationship between the method and actual physical meaning of the speaker system. To remedy this shortcoming, a mechanical vibration model is constructed to simulate the vibration behavior of the speaker system and the Rayleigh’s first integral is used to analyze the sound radiation of the speaker system. The theoretical analysis and experimental study will focus on the sound radiation of direct-radiation type of loudspeaker systems. The speaker system is modeled as a two-degree-of-freedom system which is used to study the low frequency sound radiation of the speaker system. In the range of mid to high frequency, the speaker system is modeled as a baffled speaker and the Rayleigh’s first integral is used to calculate the sound pressure generated by the speaker. The proposed method is then used to study effects of the volume of the enclosure, tube length and tube diameter on the sound radiation behavior of the speaker system. Finally, a criterion is established for the design of direct-radiation loudspeaker systems.