Measurement Method Of Sound Absorption Properties Of Acoustic Materials With Oblique Incidence

With the development in the fields of industry,environmental protection,construction and military,the impact of noise in people's lives is getting bigger and bigger.It makes people distracted,harms their hearing and can induce diseases.Therefore,people pay more and more attention to the prevention and control of noise.Sound absorbing materials are widely used today in the increasingly serious noise pollution.Sound reflection coefficient is an important parameter to characterize the acoustic properties of sound absorbing materials.It quantifies the sound absorbing properties of sound absorbing materials and provides a theoretical basis for the correct application of sound absorbing materials.Therefore,how to effectively obtain the reflection coefficient of acoustic materials has become the focus of people's research.In this paper,we mainly study the measurement method of the coefficient of sound absorption coefficient of a large sample of underwater acoustic material in a free field by using the double microphone transfer function method.Firstly,under the condition of the plane wave acoustic field and the incident of the far-field point source,the geometrical acoustics is used to approximate the condition,and the calculation method of the oblique incident acoustic performance of the material is deduced.As long as the input impedance of the material surface is consistent,no matter what kind of incidence,the reflection coefficient of the same.In order to evaluate the acoustic performance of the material more accurately,the surface impedance of the material is deduced by using the sound field conditions under point incident conditions and the continuity of sound pressure and vibration velocity at the boundary conditions.Finally,the transfer function method is used to calculate the reflection coefficient of the material by using the transfer function of sound pressure at two points along the acoustic wave propagation path in the free field.The simulation of oblique incidence of spherical wave is carried out.The effects of distance between the microphone and the surface of the material,the distance between the two microphones,the horizontal distance between the microphone and the sound source and the distance between the sound source and the surface of the material are discussed.Sensitivity and the influence of the phase inconsistency between the sound pressure and the vibration velocity channel on the test results,the influence of the deviations of the transfer function phase and amplitude calculation on the measurement is discussed.In the semi-anechoic chamber,a measurement system based on the transfer function method was set up.The reflection coefficient of the steel plate was measured and compared with the theoretical value.The two were basically the same,and the validity of the method was verified.Then,the sound absorption coefficient of sound-absorbing cotton was measured.The measured results were in good agreement with the theoretical and traditional methods in the low frequency range from 300 to 1000 Hz.The validity of the test method was verified.Provide some theoretical and experimental basis.By using the method established in this paper,the theoretical analysis of the oblique incident acoustic performance measurement of underwater acoustic materials is carried out,which provides the theoretical and experimental basis for the measurement of the oblique incident acoustic performance of a large sample of underwater acoustic materials.