The Design And Realization Of A Measurement System By Impedance Tube For Sound Absorption Coefficient And Sound Tramission Loss

The sound absorption coefficient and sound insulation of the material are two important acoustic properties,in the architecture,automotive,industrial field has a wide range of applications and research value.At present,the laboratory commonly used to measure the sound absorption coefficient and the sound insulation of the main methods are two: reverberation chamber method and impedance tube method.The advantage of using the reverberation chamber method is that the acoustic waves are random incidence and the sample can be heterogeneous and can be applied to large sample testing.But the use of reverberation chamber method to test the room has a higher demand,the cost of high cost,not easy to achieve.The advantage of using the impedance tube method is that it can measure the sound absorption coefficient,the reflection coefficient and the impedance and admittance of the acoustic incident at the time of vertical incidence,and the sample is easy to obtain.The measurement method is simple and suitable for popularization and popularization.In this paper,we use the impedance tube method to measure the sound absorption coefficient and sound insulation of the material.Based on the plane wave theory in the tube,the condition of forming the plane wave in the acoustic waveguide is deduced.In order to follow the experimental operation of the theory of bedding,the theoretical basis and the derivation of the standing wave ratio method and the transfer function method for measuring the sound absorption coefficient of the material are described in detail.This paper introduces the dual load measurement method and the theoretical basis of the four-sensor method and the derivation of the formula.The main purpose of this paper is to develop a real-time measurement system for measuring the sound absorption coefficient and sound insulation according to the international standard ISO 10534-1: 1996 and ISO 10534-2: 1998: impedance tube.These include: selection of impedance tube materials,the design of the length of the impedance tube,the design of the speaker tube,the design of the microphone hole and the way to determine the convergence.At the same time,the working principle and performance parameters of loudspeakers,microphones,data acquisition cards and signal conditioners are introduced,and a complete set of standing wave tube measuring system is built.In this paper,the transfer function method for the measurement principle,the use of MATLAB software to prepare the use of impedance tube method to measure the sound absorption coefficient and sound insulation algorithm.In order to verify the correctness of this algorithm,we use virtual.lab software to simulate the model,the impedance model of the impedance tube with the designed impedance tube is established,the simulation results are compared with the theoretical results,sound absorption and sound insulation are in good agreement.To further verify the accuracy of the impedance tube,the use of standard test pieces of polyurethane and foam rubber for sound absorption coefficient and sound insulation of the experimental measurement.The results obtained are consistent with the results of the Beijing Impression Company's impedance tube measurement,which is very effective in demonstrating the accuracy of the measurement system.Through the theoretical research and experimental verification of this paper,the feasibility and reliability of the system are fully proved.Using this impedance tube measurement system to measure several common sound absorption and sound insulation samples,for example: egg cotton,sponge,polyurethane,wood,glass,high density foam board,iron and so on.Comparing the change in the sound absorption coefficient of the sample under different conditions,obtained analysis: When the backing condition of the sound absorption sample is an air column,as the air column becomes longer,the sound absorption band moves toward the low frequency;The sound absorption coefficient of glass wool samples increases with the increase of frequency;Gypsum perforated plate backing for the sound absorption sample,the peak sound absorption coefficient becomes larger,band width and so on.And organize the experimental data to provide a reference for the sound absorption performance and sound insulation performance of the material.