Influence Of Boundary Conditions On The Measurement Of Wood Acoustic Vibration Performance

The acoustic vibration performance of wood has an important influence on the acoustic quality of musical instruments.In the past,when testing and evaluating the acoustic vibration performance of wood,the boundary conditions with free ends were used.But in the finished musical instrument,the boundary conditions of wood are not free.To explore the influence of boundary conditions on the acoustic vibration performance of wood,this article is based on the fast Fourier transform spectrum analysis method(FFT),with four boundary conditions:free boundary,simply supported at both ends,fixed at both ends,and cantilever beam,determining specific elastic modulus E/p,acoustic radiation quality constant R,ratio of dynamic elastic modulus to rigid modulus E/G,damping coefficient?,represengting energy loss per cycle of wood tan?/E,acoustic impedance w and so on,for Pica sitchenrsis and Paulownia,and analyzing the impact of different boundary conditions on the test results,and correlation between test results of different boundary conditions.The result is as follows:(1)The acoustic vibration performance of wood with different boundary conditions will be significantly different,especially the most significant impact on the friction loss in wood.Detection of acoustic vibration parameters(dynamic elastic modulus E,specific dynamic elastic modulus E/p,acoustic radiation quality constant R,acoustic impedance w,ratio of dynamic elastic modulus to rigid modulus of wood(spruce and paulownia)with different boundary conditions E/G)The relationship of size is:free boundary>cantilever beam>fixed at both ends>simply supported at both ends,compared with the free boundary condition,the cantilever beam is 7.32%-31.27%smaller,the fixed ends are 10.49%-20.20%smaller,and the simple ends are 16.85%-31.27%smaller..The relationship between the detection damping coefficient ? and the tan?/E representing the energy loss per cycle of wood is:simply supported at both ends>fixed at both ends>cantilever beam>free boundary.Among them,compared with the free boundary condition,the cantilever beam is 81.62%-113%larger,the two ends fixed is 124.56%-181.75%larger,and the two ends simply supported are 207.63%-347.87%larger.(2)The acoustic vibration parameters,dynamic elastic modulus E,specific dynamic elastic modulus E/?,acoustic radiation quality constant R,acoustic impedance w,ratio of dynamic elastic modulus to rigid modulus of wood(spruce and paulownia)with different boundary conditions E/G,of wood measured with the three boundary conditions of simply supported at both ends,fixed at both ends,and cantilever beams are correlated with the results measured with free boundary conditions.The correlation coefficient between the cantilever beam and the free boundary is 0.94-0.99,the correlation coefficient between the fixed ends and the free boundary is 0.94-0.99,and the correlation coefficient between the simply supported ends and the free boundary is 0.90-0.99.(3)In the test,the free boundary requires strict control operations to reduce the change of its geometric position,to avoid affecting the measurement results,and the operation is difficult;the simple support vibration at both ends is too fast to decay,and it is not suitable to obtain a good vibration spectrum during the test,and it is very difficult to analyze the data;it is necessary to fix the two ends to obtain a vibration signal that is sufficient for the sensor to detect,which requires a large excitation force.Excessive vibration force can easily cause damage to the wood sample,which violates the principle of non-destructive detection.Combined with the analysis of experimental operation difficulty,the cantilever beam boundary condition is the easiest to operate to detect the acoustic vibration performance of wood.This experiment has certain reference significance for the evaluation and testing of musical instrument soundboard materials.