利用振動吸震器理論做動態揚聲器之低頻延伸設計

Abstract

本論文著重在揚聲器的低頻延伸設計，從微型揚聲器到中大型的揚聲器都在本文探討的範圍裡。設計方法為利用傳統的vented-box結構，並找出最佳的音箱幾何尺寸，此時相當於機與聲兩個系統間有偶合效應的2自由度振動系統，這個系統和振動學中的振動吸震器理論非常相似，所以可以把振動吸震器理論應用在這裡。分析的平臺是利用機電聲類比電路，並使用電路學中方法，來求得揚聲器的電阻抗和軸向聲壓。為了建立一套針對vented-box的設計流程，所以先跟據振動吸震器理論來求出特徵方程式，利用此式來畫一設計圖表，這樣一來即可利用此圖表來做設計。除此之外，還可以進一步的使用這個圖表來做限制條件下的最佳化設計。本論文主旨即在列出上述的設計準則和方法。

A universal design procedure is presented for enhancing the low-frequency responses of loudspeakers ranging from handset microspeakers to subwoofers. This procedure aims at finding the optimal parameters of vented-box configuration using a systematic procedure based on vibration absorber theory. By viewing the system as two coupled serial and parallel oscillators, a characteristic equation is derived for the vented box system. A simulation platform is then established using electro-mechano-acoustical (EMA) analogous circuits. Electrical impedance and on-axis sound pressure level (SPL) of the loudspeaker can be simulated by solving the loop equations of the analogous circuit. In order to facilitate the design process of such loudspeaker systems, a design chart is devised using the characteristic equation for deciding the parameters to deliver maximal output at the low-frequency end. In addition, a constrained optimization procedure is applied to maximize the acoustic output under the enclosure constraints. Simulations and experiments were undertaken for validating the resulting optimal design. Design guidelines are summarized.