揚聲器平面彈波之疲勞壽命評估

Abstract

本文設計可用於揚聲器的平面彈波，其中利用平面空間的形狀變化來改變平面彈波的剛性，以降低揚聲器的共振頻率，並改善傳統彈波無法提供大衝程的缺點。在材料方面，本文使用編織玻璃纖維複合材料製作平面彈波，相較於麻布製作的傳統彈波，有較高的疲勞強度。在預測平面彈波疲勞壽命部分，利用有限單元分析軟體，分析揚聲器在固定功率及頻率下之振動，以識別平面彈波的應力集中部位，另配合應力-壽命曲線，推算平面彈波受到單一循環應力作用下的疲勞壽命。此外，由於揚聲器的使用並不侷限於單一頻率，所以也探討了以白噪音為訊號源時，平面彈波受到隨機負載的疲勞壽命。最後實際製作包含平面彈波的揚聲器，並進行疲勞試驗，以驗証理論方法之正確性。根據經實驗數據驗證過之分析方法，建立一個從設計平面彈波到預測其疲勞壽命之方法流程。

In this thesis, different types of plane dampers are designed for loudspeakers. The shape of the plane damper is designed in such a way that it can decrease the stiffness of plane damper which in turn can lower the loudspeaker's resonant frequency and increase the stroke of the voice coil of the loudspeaker. Regarding damper materials, the woven glass fiber composite material is used to make the plane damper of which the stress distribution may be more complex then that of the traditional corrugated damper made of gunny. The woven glass composite material has better fatigue resistance then gunny. Regarding fatigue life prediction, the finite element method is used to analyze the stress distribution and identify the danger location of the damper for the speaker vibrating at constant power and frequency. The experimentally determined S-N curve is used to predict the damper's fatigue life under a constant cyclic stress. Furthermore, the speaker is also subjected to white noise excitation to analyze the fatigue life of the damper. A number of loudspeakers which comprise plane dampers are fabricated for fatigue testing. The test results are used to verify the proposed method for fatigue life prediction. Finally, a procedure for damper design and fatigue life prediction is proposed.