- 學位論文
烏克麗麗結構動態特性與聲場之量測與分析
Structural Dynamic Characteristics and Sound Field Measurement and Analysis of a Ukulele
摘要
音樂從古至今都存在於人類文明中，樂器的歷史也可追溯至數千年前，如今，各式樂器已演變成十分複雜而精密的發聲儀器，許多學者也致力於研究樂器結構物理意義以及樂器品質之量測標準，但是，在樂音給予人主觀的感受，與物理量測之客觀數值之間的關係仍未完整建立。本文旨在應用既有固體力學量測技術對弦樂器家族中結構較為簡單而體積較輕小的烏克麗麗進行動態特性與聲音表現的量測，建立可靠而全面的量測系統，並對樂器物理結構與聲音特性的關連進行初步的分析。 在音箱結構的部分，運用電子斑點干涉術（ESPI）量測音板的共振頻率及模態振型，並利用聚偏二氟乙烯（PVDF）壓電薄膜感測器、布拉格光纖光柵感測器（FBG）及光纖位移計量測音箱表面的位移或應變量，進一步了解音箱的共振頻率和其他動態特性。對於琴弦，也就是烏克麗麗的能量來源部位，則使用高速攝影機拍攝其運動情形，搭配數位影像相關法（DIC）計算琴弦的位移，分析琴弦振動情形，並擷取其模態振型與理論進行比對，證實琴弦的振動情形與雙邊固定弦理論十分吻合。並利用麥克風及FBG量測撥弦後音箱與聲音的表現，將烏克麗麗從琴弦受力到音箱共振，至最後產生聲音的過程完整記錄並進行比較，發現音箱振動的情形及發出的聲音除琴弦傳來的頻率外，亦受音箱本身模態影響。最後再使用麥克風量測烏克麗麗正、背音板的打音，並開發音箱振動產生聲音的頻率響應量測系統，進一步了解音箱結構對聲音輸出的影響，總結出數個對烏克麗麗聲音效果影響最大的音箱共振模態。
並列摘要
Music can be found everywhere in human culture, and the development of musical instruments dates back to thousands of years ago. Musical instruments nowadays have evolved into sophisticated instruments that produce sound. Many works have been done to understand the physical interpretation of instruments’ structure and their quality, however, the relationship between mechanical measurements and perceptions of both player and listeners is still a mystery. This thesis employs many experimental techniques to establish the measurement system of ukulele and extract the features that can be used to connect its structure and sound. This study consists of three parts: the sound box, the strings and the sound of the ukulele. First of all, Electronic Speckle Pattern Interferometry is used to obtain the resonants and corresponding mode shapes of the soundboards. Also, Polyvinylidene fluoride sensor, Fiber Bragg Grating sensor and Fotonic Seneor are applied to the measurement of dynamic signals on the surfaces of soundboards. As for the strings, high speed camera along with Digital Image Correlation are used to measure the displacement of vibrating string. The dynamic response of soundboard and the output sound, while strings are plucked, are also measured and compared. Lastly, to understand the relationship between sound box structure and sound properties, tap tones of both soundboards are measured. A special measurement and analysis system is also built to measure the frequency response for ukulele’s body to produce sounds.