| 摘要: | 本研究旨在探討古典吉他弦與音箱結構之共振耦合現象。了解不僅是吉他面板振動頻率與弦音相當時會產生狼音，當弦音與音孔空氣振動頻率接近或相同時同樣會產生強耦合並形成狼音。我們將透過數值模擬及實驗兩種方式來了解當弦音掃頻經過吉他空氣共振頻率時對於吉他音色的影響。
首先，於數學模擬中透過將吉他二自由度系統的耦合數學模型，模擬了吉他音箱的面板和音孔空氣的質量，並由此擴展為吉他弦和音孔空氣間的耦合。透過實際實驗我們使用了雷射測距儀及開發聲音脈衝激發裝置，這兩種設備皆為非接觸式量測及激發，以獲得A、B古典吉他音箱的空氣共振頻率和面板模式頻率響應。接著，我們組合了一套推拉力計和電動移動平台，實現了對吉他弦的定量撥動。實驗結果將針對弦音與空氣共振頻率品質因子、耦合因子、振幅進行討論。最後，結果表明在演奏時根據具體情況選擇合適的撥弦、彈奏方式和琴弦，可以減少狼音對吉他音色的影響。
關鍵字:狼音，二自由度系統，古典吉他，雷射測距儀，非接觸激發，耦合因子。
;This study aims to investigate the resonance coupling phenomenon between classical guitar strings and the structure of the soundbox. It is understood that not only does the occurrence of beat tones happen when the vibration frequency of the guitar′s soundboard matches that of the strings, but also strong coupling and beat tones are formed when the frequencies of the strings and the air piston vibration are close or identical. Through both numerical simulations and experimental approaches, we seek to understand the impact of string frequency sweeping through the guitar′s air resonance frequencies on the instrument′s tone quality.
Initially, mathematical simulations involve coupling models of a two degree of freedom system of the guitar, simulating the mass of the soundboard and the air piston in the soundhole, which is then extended to the coupling between the guitar strings and the air in the soundhole. In practical experiments, laser rangefinders and a sound pulse excitation device, both of which are non-contact measurement and excitation tools, are employed to obtain the air resonance frequencies and soundboard mode frequency responses of Classical Guitars A and B. Subsequently, a combination of a tension gauge and an electrically driven moving platform is used to achieve quantitative plucking of the guitar strings. Experimental results will be discussed regarding the quality factor, coupling factor, amplitude, and spectral energy of string and air resonance frequencies.
Ultimately, the results indicate that selecting appropriate plucking techniques, playing styles, and strings based on specific conditions can mitigate the influence of beat tones on the tone quality of the guitar during performance.
Keywords: wolf tone, two degree of freedom system, classical guitar, laser displacement sensor, non-contact excitation, coupling factor. |
