Effect Of Edge Sealing Material On Acoustic Absorption Test Results Of Porous Sound Absorbing Material

In order to improve the acoustic performance of railway vehicles and improve the acoustic environment inside the vehicle and along the railway,experimental methods are indispensable,and providing accurate measurement results is one of the primary tasks of experimental measurement.Measuring the sound absorption coefficient of a material in a reverberation chamber is a very important experimental content.In the measurement,since the periphery of the test piece is also exposed to the sound field to increase the sound absorption of the material,the measurement result is too large.If the reflective frame is used to seal the perimeter of the test piece,more accurate measurement results can be obtained,which provides a basis for selecting suitable sound absorbing materials and performing accurate acoustic design calculations.In this paper,the gypsum board and the wood board are selected as the edge-sealing frame,and the sound absorption coefficient of the melamine sponge when the edge is not sealed and sealed is measured in the reverberation room.In the sound insulation chamber,the amount of sound insulation of the edge sealing material was measured experimentally.The sound absorption coefficient of the edge-sealing material and the vertical incident sound absorption coefficient of the sponge at the time of edge sealing were obtained by simulation calculation and experimental measurement.The main conclusions are as follows:(1)After the melamine sponge is edge-sealed,the low-frequency sound absorption coefficient changes little,and the middle and high-frequency sound absorption coefficients are greatly reduced.Usually,this causes the peak frequency to move to the low frequency.This is mainly because the sound insulation of the edge-sealing material is small,and the sound absorption coefficient of the low-frequency sound absorbing material is small.Although a large amount of sound waves are transmitted into the sound absorbing material,the sound absorption coefficient does not change much;The frequency-sealing material has a higher sound insulation,and the sound absorbing material has higher sound absorption performance,so that the sound absorption coefficient is drastically reduced after the sound energy absorbed by the material in the band is greatly reduced..(2)The weighted sound insulation of the multi-layer board,blockboard,9.5 mm gypsum board,12 mm gypsum board,low-density board and medium-density board are 25,26,28,29,31 and 32,respectively.The greater the weighted sound insulation of the edge-sealing material,the better the edge-sealing effect.However,compared to the same density of gypsum board and MDF,the weight of the MDF is 3dB higher.This may be due to the fact that the density of the MDF is larger than that of the gypsum board.(3)The sound absorption coefficients of the six edge-sealing materials are small.When using six kinds of materials to seal the edge,the sound absorption coefficient of the sponge will increase slightly,but the increase is not large,which has little effect on the test results and can be ignored.The experimental measurement shows that the sound absorption coefficient of the sponge is larger than the simulation calculation result,and the peak frequency shifts to the low frequency by one 1/3 times the frequency band.This may be due to the fact that the impedance tube is not completely rigid in the experiment,and some of the sound waves are transmitted outside the tube.(4)The six kinds of plates are easy-to-purchase plates on the market.From the consideration of price,processing performance,practical performance,sound absorption and sound insulation properties of materials,the MDF can be preferred as the edge sealing material.When selecting the edge-sealing material,if only the edge-sealing effect is considered,the surface density should be selected for the same material;for different materials,if the surface density is equivalent,the weight-of-weight should be selected.