含水率對馬林巴木琴琴鍵振動特性之影響

Effect of Moisture Content on the Vibration Characteristics of Marimba Bars

卓志隆(Chih-Lung Cho) ； 葉小雲(Hsiao-Yun Yeh) ； 吳四印(Shih-Yin Wu)

《林產工業》 27卷1期 (2008/03) Pp. 1-11

https://doi.org/10.6561/FPI.2008.27(1).1

摘要

本研究探討花梨木（Pterocarpus spp.）、巴杜柳桉（Shorea spp.）及婆羅洲鐵木（Eusideroxylon zwageri）三種木材所製成C_4~B_4之馬林巴木琴用琴鍵，在不同含水率狀態下時撓曲振動第一及第二振動模態共振頻率及內部摩擦的變化。結果顯示隨著木材含水率增加，各音名琴鍵之撓曲第一及第二共振頻率會降低；內部摩擦則會增加；第二振動模態與第一振動模態共振頻率的比值則都維持在4倍，不會隨含水率變動而有差異。從樹種間變異性分析比較結果，含水率每增加1%時，婆羅洲鐵木琴鍵之撓曲第一及第二振動模態共振頻率分別減低0.44%及0.45%；內部摩擦增加3.65%，皆顯著低於其他兩個樹種。若木材含水率變化超過2%以上時，則C_4~B_4音名琴鍵之撓曲第一及第二振動模態共振頻率差異皆超過±10音分，即會造成琴鍵音準偏差。

關鍵字

馬林巴木琴 ； C_4~B_4 音名 ； 含水率 ； 共振頻率 ； 內部摩擦

並列摘要

The purpose of this study was to investigate the influence of moisture content on the first and second mode frequencies, and internal frictions of marimba bars (from C_4 to B_4 notes) made from padauk (Pterocarpus spp.), selangan batu (Shorea spp.), and belian (Eusideroxylon zwageri) by using the flexural vibration technique. Results showed that the first and second mode resonant frequencies of wooden bars decreased and those of internal frictions increased with an increase of moisture content. However, the ratio between the first and second mode frequencies remained at 4, which was not affected by the variation of moisture content. An increase of 1% in moisture content could result in a 0.44% and a 0.45% decrease in the first and second mode frequency, respectively. For those of internal friction would increase 3.65%. The changes in resonant frequency and internal friction of belian wooden bars with moisture content were significantly lower than those of the other two species according to ANOVA analysis. If the variation of moisture content of wooden bars was over 2%, both the first and second mode frequencies discrepancy with respect to C_4 to B_4 notes would exceed ±10 cents. This would result in an incorrect pitch of each marimba bar.

並列關鍵字

Marimba bars ； C_4 to B_4 notes ； Moisture content ； Resonant frequency ； Internal friction