Measurement Of Sound Absorption Coefficient Of Underwater Acoustic Materials Based On Reverberation Method

The sound absorption coefficient is an important criterion for measuring the performance of sound absorbing materials.In aeroacoustics,the reverberation chamber method is a classical method for measuring the average sound absorption coefficient of random incidence of materials.Compared with the reverberation environment in the air,the underwater reverberation environment has a shorter reverberation time and a more uneven distribution of the low-frequency sound field.Therefore,there are more uncertain factors when using the reverberation method to measure the sound absorption coefficient of underwater acoustic materials in underwater closed space.Therefore,it is of great significance to carry out the exploration of measuring the sound absorption coefficient of underwater acoustic materials based on the reverberation method.In this paper,the reverberation chamber method is applied to measure the sound absorption coefficient of underwater acoustic materials in the reverberant water tank,and the effectiveness and influencing factors of the sound absorption coefficient of the material are measured by experimental reverberation method.Firstly,the sound field in the rectangular reverberation tank is analyzed.And the formula for calculating the reverberation time in a rectangular reverberation tank has been derived from the theory of wave acoustics and statistical acoustics.Also,it is proposed to use the reverberation method to measure the sound absorption coefficient of the material in the reverberation tank.The formula for calculating the sound absorption coefficient of materials is derived.The reverberation time in the empty tank state of the reverberation tank is measured and the sound absorption coefficient of the tank wall is obtained.Secondly,the experimental study on the factors affecting the sound absorption coefficient and the sound absorption coefficient measurement of the underwater acoustic material using the reverberation method in the reverberation tank is carried out.The results show that the sound field in the reverberant tank does not meet the diffusion field conditions,which results that the placement of the test piece using the centralized deployment method has great influence on measurement results of sound absorption coefficient of underwater acoustic materials in a lower frequency band.It is best to place the test piece on the center of the tank surface.The measurement error is related to the area of the test piece when the sound absorption coefficient of the material is measured by the centralized deployment method.The area of the best test piece is related to the ratio of the length to the width of the test piece and the area of the water tank.This paper gives the test piece size and placement recommendations for the best test piece area.Finally,a method for improving the measurement accuracy of material sound absorption coefficient by distributed deployment is proposed.The experimental results show that in the case of the same area,the measurement accuracy of distributed deployment is better than that of centralized deployment.When the conditions permit,the larger the spacing of distributed deployment,the higher the measurement accuracy of sound absorption coefficient,and the measurement result of sound absorption coefficient is more close to the true value.This measurement method has an important guiding role in the measurement of random sound absorption coefficient of materials in closed spaces.