臺灣博碩士論文加值系統

本研究探討花梨木、巴杜柳桉、婆羅洲鐵木、台灣櫸與相思樹等五種樹種，在不同長度挖空比值及深度挖空比值下，對各振動模態共振頻率、內部摩擦及頻率比值的影響。結果顯示挖空長度之增加，各振動模態之共振頻率會減低，內部摩擦會增大，利用挖除位置對各不同彎曲振動模態頻率的影響差異，可調整其頻率比值。若與傳統用馬林巴木琴材料花梨木比較，巴杜柳桉在彈性係數、內部摩擦等音響指標上皆優於花梨木，值得開發。
並以花梨木、巴杜柳桉及婆羅洲鐵木樹種，探討含水率、年輪傾斜角與塗裝對木琴振動特性之影響。隨著含水率增加，各音名琴鍵之彎曲第一及第二振動模態頻率會降低，內部摩擦會增加，但f2 / f1的比值都維持在4，不隨含水率而有差異；若含水率變化超過2%以上，則C4 -B4音名琴鍵之第一、二振態頻率差異皆超過±10音分，即會造成木琴琴鍵音準偏差。年輪傾斜角為0°時，內部摩擦較低，隨著年輪傾斜角之增大，內部摩擦有增大之趨勢，這點對音響樂器用材是不利的。木琴經塗裝後，C4 -B4音名琴鍵之第一、二彎曲振動共振頻率皆隨著塗佈量遞增而遞減，內部摩擦則隨塗佈量增加而增大，但f2 / f1的比值都維持在4，不受影響。此外，塗裝可減少木材之吸脫濕性所引起的水分變化，進而減低木材的膨潤收縮性；相對地塗裝後之木琴琴鍵的振動特性較不易受到環境相對濕度影響造成聲音品質的變化。從共振頻率減低率，內部摩擦增加，塗裝操作難易性，塗料成本等評估塗裝對木琴琴鍵音響性質影響時，建議採用桐油且避免厚塗。

The first purpose of this study was to investigate the influence of parabolic undercuts on the natural frequency, internal friction, and ratios between natural frequencies of padauk (Pterocarpus spp.), selangan batu (Shorea spp.), belian (Eusideroxylon zwageri), Taiwan zelkova (zelkova formosana), and Taiwan acacia(Acacia confusa) wooden bars. Results showed that first three natural frequencies obtained from flexural vibration test decreased with an increase in undercut ratio, and those of internal friction corresponding to each vibration mode would increase. Removing material from any point on a bar affected all the natural frequencies to some extent. However from this study it is clear that removal from certain places affects some modes more than the others, and thus it is possible to tune the frequencies of a wooden bar in harmonic. Based on the values of MOE and internal friction, selangan batu could be a possible option for marimba bar material.
The second aim of this study was to investigate the effects of moisture content, annual ring angle, and coating on the vibrational characteristics of padauk, selangan batu, and belian wooden bars. The first and second mode frequencies of wooden bars decreased and those of internal friction increased with an increase of moisture content. However, the ratio between first two frequencies remained at 4, which was not affected by the variation of moisture content. If the change of moisture content of wooden bar over 2%, the first and second mode frequencies discrepancy with respect to C4-B4 notes will exceed ±10 cents. This will result an incorrect pitch of each marimba bar. The internal friction of wooden bars at 0 degree annual ring angle was the lowest. Values of internal friction increased with an increase in annual ring angle, and this situation is not suitable for musical instruments. The first and second bending mode frequencies of wooden bars corresponding to C4-B4 notes decreased with an increase in coating weight percentages, and those of internal friction would tend to increase. But the ratio of f2/f1 would not affect by coating process. The dimensional stability and moisture-sorption behavior would be improved using coating process , so the acoustical qualities of marimba bars will less affected by relative humidity. It is suggested using thin tung oil coating for marimba bars in respect of variations of natural frequency and internal friction, operational processes and cost of different coatings.

中文摘要…………………………………………………………………… ⅰ
英文摘要…………………………………………………………………… ⅱ
誌謝………………………………………………………………………… ⅳ
目錄………………………………………………………………………… ⅴ
表目錄……………………………………………………………………… ⅶ
圖目錄……………………………………………………………………… ⅸ
壹、前言…………………………………………………………………… 1
貳、前人研究……………………………………………………………… 3
一、木琴琴鍵之結構振態分析……………………………………… 3
二、木琴之調音與製作方法………………………………………… 4
三、琴槌種類與琴鍵敲擊位置對振動特性之影響………………… 5
四、含水率對樂器音響性質之影響………………………………… 6
五、塗裝對樂器音響性質之影響…………………………………… 6
叁、材料與方法…………………………………………………………… 9
一、試驗材料………………………………………………………… 9
二、試驗方法………………………………………………………… 11
肆、結果與討論…………………………………………………………… 18
一、底部挖空處理對木材振動特性之影響………………………… 18
二、含水率對音響特性之影響……………………………………… 34
三、年輪傾斜角對音響特性之影響………………………………… 43
四、塗裝對音響特性之影響………………………………………… 48
伍、結論…………………………………………………………………… 62
參考文獻…………………………………………………………………… 64
附錄………………………………………………………………………… 68

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