Research On Acoustical Vibrational Response Of Soundboard Wood Under Axial Loading

In order to study the effect of axial load on the acoustic vibration and acoustic response characteristics of soundboard wood,and to understand the sound mechanism of wood materials,this paper uses paulownia and spruce soundboard wood as the research object to preliminarily simulate the effect of soundboard wood in piano assembly.Constraint and axial load,use dual-channel fast Fourier transform spectrum analyzer(FFT)to detect the acoustic vibration performance of soundboard wood under 0-1600 N axial load,and analyze the change law of various acoustic vibration parameters;Scanning electron microscope was used to observe the changes in the microstructure of the soundboard wood;the single-point pick-up method was used to conduct a modal vibration test on the soundboard wood under axial load,and to analyze the changes in the mode diagrams of each order,from the microstructure and modalities The theoretical point of view is to study the mechanism of axial load affecting the acoustic performance of soundboard wood.The main conclusions of this paper are as follows:(1)Within the scope of the test,the axial compression load is significantly negatively correlated with the acoustic parameters of the soundboard wood.For every increase of 200 N in the axial compression load,the specific dynamic modulus of paulownia,sound wave propagation velocity,and sound radiation Quality constant,acoustic conversion efficiency and acoustic impedance are respectively reduced by 3.0(± 1.0)%,1.7(±0.5)%,1.3(±0.6)%,10.0(±1.0)%,2.0(±1.0)%,loss tangent Increase by 9.3(±2.7)%;Spruces specific dynamic elastic modulus,acoustic wave propagation velocity,acoustic radiation quality constant,acoustic conversion efficiency and acoustic impedance decrease by 1.8(±0.9)%,1.0(±0.3)%,1.1(±0.4)%,8.6(±3.9)%,0.7(±0.4)%,the loss tangent increased by 9.9(±3.8)%;the comprehensive scores of paulownia and spruce decreased by 4.9(± 1.8)%?4.9(±1.4)%.Through SEM observation,it is found that the normal and straight cell wall has different degrees of wrinkles due to axial compression,which is an important reason for the decline in the acoustic performance of the soundboard wood.(2)Within the test range,there is a significant positive correlation between the axial tensile load and the acoustic parameters of the soundboard wood.For every 200 N increase in axial tensile load,the specific dynamic elastic modulus,sound propagation velocity,sound radiation quality constant,sound conversion efficiency and acoustic impedance of paulownia increase by 3.8(±1.3)%,1.9(±0.6)%,2.4(±0.7)%,11.4(±5.0)%,1.4(±0.5)%,loss tangent reduced by 5.6(±2.6)%;spruce specific dynamic elastic modulus,sound wave propagation velocity,sound radiation quality constant,Acoustic conversion efficiency and acoustic impedance increased by 2.7(±1.0)%,1.3(±0.5)%,1.8(±0.5)%,10.7(±6.7)%,0.9(±0.6)%,respectively,and the loss tangent decreased Smaller 5.6(±3.5)%;the comprehensive scores of paulownia and spruce increased by 4.0(±2.7)%,3.9(± 2.6)%respectively..Through SEM observation,it is found that the normal,straight cell wall does not change significantly under the action of axial tensile load,because the tensile strength of wood is much greater than the compressive strength of the grain.The main factor to improve the acoustic performance of the soundboard is the increase in the stiffness of the material.(3)As the axial compression load increases,the middle node of the second-order mode shape of the soundboard wood has a tendency to shift to the left,and the middle two nodes of the third-order mode diagram have a tendency to shift apart;with the axial direction As the tensile load increases,the middle node of the second-order mode of the soundboard wood tends to shift to the right,and the middle two nodes of the third-order mode diagram tend to shift closer to the shift.The mode shape is only related to the quality,stiffness and constraint conditions of the structure.In this test,the quality is assumed to be unchanged,and the constraint condition is fixed at both ends.Therefore,the axial load changes the stiffness of the material,which is an important factor in the acoustic vibration characteristics of the soundboard wood.