Acoustic Performance Test And Analysis Of Inner Soundproof Pad Of Automobile Dash

The use of acoustic packages is a necessary means to reduce vehicle noise and improve vehicle inerior acoustic quality,and it is of practical significance in design and measure of acoustic package's acoustic performances.At present,the commonly used acoustic performance evaluation indicators include sound absorption coefficient and transmission loss,and their associated measurement methods have their own advantages and disadvantages.In this paper,the measurement methods of sound absorption coefficient and transmission loss were analysised and discussed,and associated experiments were conducted in order from parts to whole,and as a result,the acoustic performance testing and lectotype of a certain sound-proof pad was done.Furthermore,the prediction of sound absorption coefficient of fibre acoustic materials which were commonly used in vehicle acoustic packages was attempted,in order to provide a reference for material selection and forward design.Firstly,the measuring method and principle of sound absorption coefficient and transmission loss based on impedance tube was analysised and discussed,and the sound absorption coefficient and transmission loss of two kinds of acoustic materials,double impedance felt and EVA+PU foam,were tested.The results show that: the sound absorption property of double impedance felt is better than that of EVA+PU foam and the transmission loss of EVA+PU foam is better than that of double impedance felt,both of them have the equivalent comprehensive acoustic performance,but the gram weight of double impedance felt is 300 g/m2 lower than that of EVA+PU foam,for the purpose of lightweight,the double impedance felt was selected as the material for inner soundproof pad.Subsequently,the measurement method and principle of sound absorption coefficient and transmission loss based on acoustic laboratory are analyzed.The sound absorption coefficient was measured based on the reverberation-room method,and the transmission loss was measured based on the reverberation-room and anechoic-room method with sound intensity testing,at the same time,the influence of the location of microphones,sound source and the specimens on the measurement results is discussed.The results show that: the average sound absorption coefficient is about 0.51 dB,and the average transmission loss is about 15.2 dB in 500-6300 Hz frequency band.The arrangement of microphones,sound source and specimens would affect the measurement results,and the lower the frequency,the greater the impact.In order to obtain relatively accurate measurement results,sound source could be placed in corners and measured with as many indoor arrangement combinations as possible.The weak position of sound insulation of the inner soundproof pad are the installation hole of the direction pillar and the air-conditioning intake port.Lastly,the prediction of sound absorption coefficient of double impedance felt fiber material based on Delany-Bazley-Miki model and transfer matrix method is realized by MATLAB.The prediction result is basically equivalent with the overall trend of the test results.