微型揚聲器振膜刻痕最佳化與低頻延伸設計

Abstract

今日用於行動配備的微型揚聲器總是被需求微小化、高輸出等級、高聲音品質等特性，但這些需求都存在著矛盾關係。相對於大型揚聲器，微型揚聲器的結構簡化了懸吊裝置。微型揚聲器振膜的作用不僅可以幅射出聲音亦可以當作懸吊系統。因此振膜上的刻痕設計對於微型揚聲器的性能與頻率響應是很重要的。傳統用集中參數的方法一般是不足以模擬到振膜高頻撓性共振的模態，因此在這篇論文中結合了有限元素分析與機電聲類比電路的方法，比起以往傳統的方法能夠更準確的模擬出微型揚聲器的性能。尤其在計算音圈與振膜機械阻抗時，是利用有限元素分析來求得的，再將所求得的機械阻抗代入機電聲類比電路的機械系統中，接著求解機電聲迴路方程式即可模擬微型揚聲器的性能響應。以此模擬平臺，使用田口分析法對振膜刻痕做最佳化分析，另外再利用敏感度分析求得振膜最佳刻痕數。在此篇論文中也提到結合有限元素分析與集中參數的方法來模擬音箱系統及利用約束最佳化方法對音箱尺寸做最佳化分析。另外也提到結合類神經網路與模擬退火法對微型揚聲器振膜做最佳化分析。

Today’s microspeakers of portable devices are demanded to meet a number of conflicting requirements including miniaturization, high output level, good sound quality, etc. In contrast to large loudspeakers, the structures of microspeakers are generally simplified enough with suspension removed. The diaphragm serves as not only a sound radiator but also the suspension. Thus, the pattern design of the diaphragm is crucial to the overall response and performance of a microspeaker. Traditional approach for modeling microspeakers using lumped-parameter models is generally incapable of modeling flexural modes in high frequencies. In this paper, a hybrid approach that combines finite element analysis (FEA) and electro-mechano- acoustical (EMA) analogous circuit is presented to provide a more accurate model than the conventional approaches. In particular, the minute details of diaphragms are taken into account in calculating the mechanical impedance of the diaphragm-voice coil assembly using the FEA. The mechanical impedance obtained using FEA is incorporated into the lumped parameter model. The responses can be simulated by solving the loop equations. On the basis of this simulation model, the pattern design of the diaphragm is optimized using the Taguchi method. In addition, the optimal number of diaphragm corrugations is determined by using sensitivity analysis. The responses of vented-box system are also simulated using FEA-lumped method in this thesis. In addition, a constrained optimization procedure is applied to maximize the acoustic output under vented-box system based on FEA-lumped method. Another optimal approach of diaphragm employs the neural network and simulated annealing (NNSA).