以結構設計優化壓電式喇叭音頻響應的研發

Abstract

本文將提出一種以結構設計的方式來改變壓電式喇叭的振動行為進而優化其音頻響應。一般來說，壓電喇叭具有高Q值的特性，使得其頻率響應在共振頻附近會有非常地尖銳的起伏，這種特性限制了壓電喇叭的應用範圍。本文所做的探討將不侷限於一般喇叭研發僅針對其剛體運動部分的改善，而是更完整地分析振動板的所有振動模態與其產生聲壓之關聯性，並以優化其音頻響應為目的以結構設計方式對振動模態作被動式的控制。此方式能抑制過高聲壓的振動幅度並破壞因對稱相消性而使聲壓低弱的對稱型模態，使其能有效改善壓電喇叭的音頻響應。此外，一種針對壓電式喇叭的陣列組合模式也將在本文提出。設計過程中並以有限元素分析法來作為輔助工具，透過結合結構改善與陣列組合設計，能有效改善陣列式壓電喇叭的音頻響應，未來將能使此種具體積輕薄與高效率之喇叭廣泛應用在各類視聽產品上。

An effective structural design for a piezoelectric loudspeaker with improved frequency response is proposed in this thesis. Typically, piezoelectric loudspeakers possess a high quality factor Q and are characterized by sharp peaks near the resonance. However, the sharp resonant peaks limit the wider applicability of piezoelectric-based loudspeakers. We analyzed the relationship between all mode shapes of vibrating plate and sound pressure level instead of most design which only discussed rigid motion. According to Raleigh’s integral for sound radiation, not all the resonant modes of a vibrating plate can produce an effective sound pressure response in far field. One of the methods to get around this limitation is to excite multiple positions at the vibrating plate. In this thesis, we adopted a passive control to vary the vibrating behavior. In our setup, we used structural design to remove and to restrain certain mode shapes that could produce a much lower or higher sound pressure than the average. Furthermore, a combinative method for piezoelectric loudspeaker is brought up to improve the performance of piezoelectric loudspeaker. By choosing an effective structural design and appropriate combination by using Finite Element Method, we can obtain an ideal frequency response curve of the piezoelectric loudspeaker which can be flattened to satisfy the requirements for a loudspeaker. The applications of this high potential and miniaturizable piezoelectric loudspeaker can be extended through this improvement.