二胡是中國文化的傳統民族樂器，但海峽兩岸迄今對於二胡的改良尚乏以嚴謹的科學方法來改良二胡，大部分係以傳統之主觀判斷方式以及嘗試錯誤法來進行修改，因此有時會受阻於錯誤的推論或經驗的失傳等因素，而對於製琴技藝的提升仍有窒礙。

故本論文目的以有限元素法與邊界元素法模擬二胡琴體之結構與空腔的振動，並經由先前所建立的樂音指標來探討琴皮之各項參數（張力、厚度以及密度等）與琴筒空腔內的各參數（小琴筒長度、直徑與位置等）對二胡音色的影響。

本文利用Pro/E建立二胡幾何模型，並以有限元素分析軟體MSC Nastran模擬二胡結構動態分析，此部份數值模型皆以模態測試結果或理論值逐步進行調校，以確保其正確性。再將此結果匯入邊界元素軟體LMS Virtual Lab分析琴皮與空氣間相互作用後的聲功率頻譜，進而根據已建立的悶、穿透力以及亮度指標，分別探討小琴筒與琴皮參數的影響。從模擬結果得知，小琴筒之長度、直徑以及位置對不同的指標各有影響，可根據二胡對音色之不同需求加以調整，而在本研究之模擬範圍內，降低琴皮之張力、增加其密度或厚度皆可使得此把二胡較不悶並增加其穿透力與亮度。建立此分析方法將可幫助了解二胡之各參數對其聲音品質之影響，進而達到改良二胡的目標。

Erhu is a traditional Chinese music instrument, but researchers, either from mainland China or from Taiwan, have yet proposed a scientific and well-integrated method for improving this cultural heritage. Most of the adjustment made on erhu relies heavily upon traditional subjective methods or the trial-and-error approach. Consequently, erhu making skills are hindered by either erroneous inferences or lost of experiences.

The purpose of this study is to adopt the finite element and the boundary element approaches to simulate the structure of erhu and the vibration at its cavity. The authors applied the previously established sound quality index to discuss the effect of erhu skin parameters, including tension, thickness and density, and erhu tube cavity parameters, including length of the small tube, diameter, and location, on the timbre of erhu.

This study adopted Pro/E to construct an erhu geometric model and used finite element analysis software MSC Nastran to simulate erhu’s structural dynamics. For accuracy, the numerical model was adjusted according to the results of model testing or the theoretical values. The obtained data were imported into boundary element software LMS Virtual Lab for analyzing the acoustic power spectrum after the interaction between the erhu skin and air. Afterward, the authors discussed the effects of erhu’s small tube and skin parameters based on the established stuffiness, penetration, and brightness indices. Our simulating data suggest that the length, diameter and location of small tube each has its specific impact on the indices, and thus the timbre of erhu can be adjusted according to the needs. Within the scope of simulation, this study has found that by reducing the tension or increasing the density or thickness of erhu skin, stuffiness can be reduced while penetration and brightness of the timbre of erhu can be increased. This established method can be used for understanding the effects of assorted parameters of erhu on the acoustic quality and for further improving this instrument.

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