Theoretical Analysis and Experimental Measurements on the Influence of Dynamic Characteristics for Diaphragm, Port and Tuning Cloth in Loudspeaker System

隨著科技發展日新月異，人們對於揚聲器品質的要求也愈來愈高，尤以近年來電聲產業的蓬勃發展，使電聲產品朝向輕薄短小，強調攜帶方便的特點發展。雖說揚聲器的發聲原理相當簡單，也是一項發展許久的技術，但要做出具有好音質且低失真的完美揚聲器，卻是相當艱難的任務，且每個人對聲音的喜好亦不相同，如何製作出能滿足不同使用者的揚聲器，更是個值得討論的課題。 本文針對振膜、導音管及調音布等材料結構對於揚聲器系統動態特性的影響分析與量測作深入探討，內容主要分為三個部份，首先是藉由替換調音布及導音管之條件，量測相應的阻抗曲線，並以集總參數模型對實驗阻抗作曲線擬合，找到與實際情況最接近的模擬阻抗，得到最佳之聲學阻尼係數；第二部份將針對小型低音反射式音箱產生寬帶噪音的問題進行實驗量測與特性分析，以有限元素軟體及駐波理論和風切音頻率作比較，並對導音管的流場以粒子影像測速儀進行可視化實驗，找出風切音的來源並嘗試改善；最後的主題是研究關於音膜材料之機械特性，主要藉由實驗量測的方式，利用材料試驗機量測不同厚度材料音膜之彎曲剛性，且以光纖位移計擷取系統的時域動態訊號，運用振動學原理得到各個頻率下不同厚度材料音膜之阻尼比。With the rapid development of technology, the need for high quality of loudspeaker are increased. Electro-acoustic industry especially focus on the development of speakers, to make products more lighter, smaller, and easy to carry. Although the working principle of speakers is quite simple and the technology of speakers has been developed for a long time. However producing a high-quality speaker with good voice and low distortion is still a difficult task. Preference for voice is different for people, so it is an important topic to design a perfect speaker to satisfy different users. The main object of this research is focused on theoretical analysis and experimental measurements on the influence of dynamic characteristics for diaphragm, port and tuning cloth in loudspeaker system. The content of this thesis is divided into three parts. First, we measure the experimental impedance curve for combining of different length of port and porosity of tuning cloth. Then the Lumped Parameter model is used for the simulation of impedance. The coefficient of acoustic resistance is determined from the best fit of the theoretical prediction and experimental measurement of impedance curve. The second part of this thesis is to perform the analysis to identify the characteristics of broad-band noise generated from small bass-reflex loudspeaker. We compare resonant frequency of chuffing with the results predicted by the finite element analysis and the theory of standing wave. Furthermore, we identify the chuffing noise by Particle Image Velocimetry to visualize the flow field. Finally, an effective method is proposed to decrease the intensity of noise. The last topic of this thesis is to study the mechanical characteristics of materials for diaphragms by experimental measurement. The stiffness of the diaphragm is determined by the indentation of the thin film for diaphragms. The damping ratio of the diaphragm in different frequency is obtained by measuring the dynamic signals of the diaphragm base on the vibration theory