四種闊葉樹木材作為木琴琴鍵之音響性質評估

由於傳統木琴琴鍵用材如宏都拉斯黃檀、非洲花梨木等熱帶地區木材資源取得逐漸困難，本研究選用具開發潛力之馬氏鐵木（Eusideroxylon malagangai）、馬蹄豆木（Martiodendron parviflorum）、圭亞那乳桑（Bagassa guianensis）及臺灣相思樹（Acacia confusa）等四種闊葉樹木材，應用兩端自由之彎曲振動法探討其音響性質，作為木琴琴鍵製作之適用性參考。依音響性質評估結果顯示四種木材中，馬蹄豆木最適合作為木琴琴鍵材料；臺灣相思樹由於彈性模數較低且內部摩擦較高，不適合作為木琴琴鍵使用。彎曲基本共振頻率與內部摩擦間呈顯著正相關關係，決定係數R^2值為0.73。隨著含水率增加，木材之聲音轉換效率呈顯著地降低，含水率每增加1%時，馬氏鐵木、馬蹄豆木、圭亞那乳桑及臺灣相思樹之聲音轉換效率平均分別減低12.0%、10.1%、16.7%及9.3%。

關鍵字

闊葉樹木材；木琴琴鍵；音響性質；含水率；細長比

並列摘要

With respect to increasingly difficult to obtain preferred wood resources for traditional xylophone bars, such as Honduras rosewood, African padauk etc. from tropical regions. Four hardwood species with potential developments for xylophone bars including ulin (Eusideroxylon malagangai), tatabuballi (Martiodendron parviflorum), tatajuba (Bagassa guianensis), and Taiwan acacia (Acacia confusa) were chosen as testing materials in this study. A free-free flexural vibration method was used to investigate the acoustical properties for providing information on their suitability for xylophone bars making. The experimental results showed that tatabuballi was the most suitable material for making xylophone bars regarding to the acoustical properties of wood. While Taiwan acacia is not a suitable material for making xylophone bars due to its lower modulus of elasticity and higher internal friction. The internal friction of wooden bars was significantly correlated with resonant frequency determined from flexural vibration (R^2 is 0.73). The acoustical conversion efficiency (ACE) of wooden bars decreased with an increase of moisture content. An increase of 1% in moisture content could lead to a 12.0%, 10.1%, 16.7%, and 9.3% decreased in ACE of ulin, tatabuballi, tatajuba, and Taiwan acacia, respectively.

並列關鍵字

Hardwood ； Xylophone bars ； Acoustical properties ； Moisture content ； Slenderness ratio

國際替代計量

四種闊葉樹木材作為木琴琴鍵之音響性質評估

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