裂纹长度对泡桐木材声学振动性能的影响

Effect of crack length on acoustic vibration properties of Paulownia wood

乐器音板易出现裂纹,而裂纹会对音板的声学振动性能产生影响。本研究以泡桐木材为对象,人工预制了不同位置、不同长度的裂纹,利用双通道快速傅里叶变换频谱分析仪对裂纹长度为0~4/8 L的端部、中部裂纹的泡桐木材声学振动性能进行检测。发现端部裂纹振动频谱一阶频率不随裂纹长度变化而变化,但高频部分随裂纹出现会出现双峰,且裂纹长度越大,对高频部分影响越大。中部裂纹对振动频谱无明显影响。二至五阶的比动弹性模量(E/ρ)和声辐射品质常数(R)、一至五阶的声阻抗(ω)和动弹性模量与动态刚性模量之比(E/G)以及损耗角正切(tanδ)与端部裂纹长度呈显著的线性相关,一阶的E/ρ和R与端部裂纹长度的相关性较弱。当端部裂纹长度为1/8 L时,一阶的E/ρ、R、ω,五阶的E/G以及tanδ几乎不产生变化;端部裂纹长度为4/8 L时,四阶的E/ρ、R、ω,一阶的E/G以及tanδ变化率最大,分别为-3.0%,-1.3%,-1.7%,8.8%和24.3%。一至四阶的E/ρ和R、一至五阶的ω和E/G与中部裂纹长度呈显著的线性负相关。当中部裂纹长度为1/8 L时,二阶的E/ρ和ω、三阶的E/G几乎不产生变化,中部裂纹长度为2/8 L时,二阶的R几乎不产生变化。中部裂纹长度为3/8 L时,一阶的E/ρ、R、E/G变化率最大,分别为-1.3%,-0.5%和-5.1%;中部裂纹长度为4/8 L时,一阶ω变化率最大,但仅为-0.8%。tanδ与中部裂纹长度的关系不明显。结果表明:裂纹长度和泡桐木材声学振动性能有较强的规律性,端部、中部裂纹对泡桐木材声学振动性能有不同影响。

Musical instrument soundboards are prone to cracks,which can affect the acoustic vibration performance of the soundboard,and there is limited research on it.In this study,cracks of different positions and lengths were artificially created in the boards.The acoustic vibration performance of Paulownia wood with cracks of 0-4/8 L in the end and middle were detected using the dual channel fast Fourier transform(FFT)spectrum analyzer.It was found that the first frequency of the end crack vibration spectrum did not change with the crack length,but the high frequency part would have double peaks with the crack appearance,and the larger the crack length was,the greater the influence on the high frequency part had.The middle crack had no obvious influence on the vibration frequency spectrum.The second to fifth order E/ρ and R,the first to fifth orderωand E/G,and tanδ were significantly linear with the end crack length.The first order E/ρand R had a weak correlation with the end crack length.When the end crack length was 1/8 L,the first order E/ρ,R,ω,fifth order E/G,and tanδhardly changed.When the end crack length was 4/8 L,the fourth order E/ρ,R,ω,first order E/G,and tanδhad the largest change rates,which were -3.0%,-1.3%,-1.7%,8.8%,and 24.3%,respectively.E/ρand R of the first to fourth order,ωand E/G of the first to fifth order were significantly negatively correlated with the length of the middle crack.When the length of the middle crack was 1/8 L,E/ρandωof the second order and E/G of the third order were almost unchanged.When the length of the middle crack was 2/8 L,R of the second order was almost unchanged.When the length of the middle crack was 3/8 L,E/ρ,R and E/G of the first order had the largest change rates,-1.3%,-0.5% and -5.1%,respectively.When the length of the middle crack was 4/8 L,ωof the first order had the largest change rate,but only -0.8%.The relationship between tanδand the length of the middle crack was not obvious.The results showed that there was a strong regularity between the crack length and the acoustic vibration performance of Paulownia wood,and the end and middle cracks had different effects on the acoustic vibration performance of Paulownia wood.