Study On Method Of In-situ Measurement Of Sound Absorbing Coefficient Of Acoustic Materials

Traditional sound absorbing coefficient measurement methods are mainly standing wave tube method and reverberation room method.Both of them have certain limitations in practical applications,for example,the sample size of the tested material must match with the size of standing wave tube in standing wave tube method,expensive reverberation room and diffuse sound field are demanded in reverberation room method.To solve this problem,method of in-situ measurement of sound absorbing coefficient of acoustic materials whose measuring equipment is microphone array is studied in this thesis.The method is based on statistically optimal acoustic wave separation method,in-situ measurement of sound absorbing coefficient of acoustic materials is carried out by achieving the separation of incident and reflected acoustic waves.The calculation model of method of in-situ measurement of sound absorbing coefficient of acoustic materials is derived,and in-situ measurement experiment for rubber material and sponge is developed,whose results are compared to the results measured by impedance tube method,results show that measurement error of this measurement method is less than 20%in the frequency range of 500Hz?5000Hz.The composition of this paper is as follows:In the first chapter,background and significance of this study are introduced,domestic and foreign research status of method of in-situ measurement of sound absorbing coefficient of acoustic materials and acoustic wave separation method are reviewed systematically,research method of in-situ measurement of sound absorbing coefficient of acoustic materials is elaborated.In the second chapter,the mathematical model of statistically optimal acoustic wave separation method is derived,numerical simulation is developed,and simulation analysis for number of microphones and microphone spacing of the array is carried out,simulation results show that the relative error of acoustic wave separation which is achieved by statistically optimal acoustic wave separation method is less than-10dB in the frequency range of 500Hz?5000Hz.In the third chapter,experimental validation about statistically optimal acoustic wave separation method is developed in anechoic chamber,data collection of different frequencies is carried out by self-developed 2x5x5 double microphone square array,and four different combinations of sound sources are studied,experimental results prove that,in the frequency range of 500Hz?5000Hz,the relative error of acoustic wave separation which is achieved by statistically optimal acoustic wave separation method is less than-0.5dB in the case of four different combinations of sound sources.In the fourth chapter,according to statistically optimal acoustic wave separation method,the calculation model of method of in-situ measurement of sound absorbing coefficient of acoustic materials is derived,in-situ measurement experiment and impedance tube verification experiment on rubber material and sponge are developed,and two experimental results are compared and analyzed,results show that measurement error of method of in-situ measurement of sound absorbing coefficient of acoustic materials which is studied in this paper is less than 20%in the frequency range of 500Hz?5000Hz.Finally,the main results in this thesis are summarized,the limitation of this research method and the content which need have a further research in the future are indicated.