Study On Multilayer Materials Sound Absorption Based On Complex Characteristic Test

Porous sound-absorbing materials are one of the most commonly used noise reduction tools,it is beneficial to the improvement of the acoustic environment and widely used in public sites.At present,there is a general focus on the sound absorption studies of single-layer porous sound-absorbing materials.However,there are not many sound absorption studies about multilayer materials composed of different porous sound-absorbing materials,especially the sound-absorbing calculation and performance optimization of multilayer materials.Therefore,this paper is devoted to studying the sound absorption characteristics of multilayer materials,improving the sound absorption performance,and enriching the studies in the sound absorption field of multilayer materials.This paper uses the standing wave tube experiment to measure the acoustic impedance ratio in two cases,including no cavity behind the material and a quarter-wave cavity behind the material.Then,according to the impedance method,the complex characteristic impedance and the complex wave number of each layer material are obtained,combining transfer matrix method to establish sound-absorbing calculation model of multilayer materials.The model has strong applicability and can meet the sound-absorbing calculation of multilayer materials under different configurations.In addition,it can estimate sound absorption performance,simplifying complicated experimental work.In this paper,two-layer materials and three-layer materials are taken as examples to study their sound absorption characteristics.The sound absorption coefficients of two-layer and three-layer materials are measured by standing wave tube experiment.The results show that the calculation results agree well with the experimental results,verifying the validity and accuracy of the transfer matrix method,and ensuring the reliability of the measured acoustic parameters.The transfer matrix method replaces the standing wave tube experiment to study the effect of the placement order and thickness distribution of each layer on the sound absorption performance,avoiding the complexity of the experiment.The results show that the placement order and thickness distribution affect the sound absorption effect of the multilayer material in different frequency bands.Therefore,according to the model,reasonable placement order and thickness distribution can improve the sound absorption effect of multilayer materials.The genetic algorithm is used to optimize the sound absorption performance of multilayer materials,in order to obtain the best sound absorption effect.The results show that the optimized sound absorption effect is far better than the unoptimized sound absorption effect.For the two-layer material,the optimized average sound absorption coefficient is 0.76,the sound absorption coefficient is above 0.9 and the peak value is 0.98 in the low-frequency range of 550 Hz to 1100 Hz.For the three-layer material,the optimized sound absorption coefficient is above 0.8 in the broad frequency range of 400 Hz to 2000 Hz.Compared to unoptimized conditions,the average sound absorption coefficient is increased by 0.3.However,if the thickness of the two-layer or three-layer material is above 70 mm,the optimization result will not change any more,so optimization is performed within a certain thickness range,which helps achieving the best sound absorption performance and saving the use of the material.This paper studies the sound-absorbing characteristics of dense materials combined with loose materials based on the density degree of porous sound-absorbing materials.The results show that adding a thinned dense material in front of a loose material improves the mid-low frequency sound absorption of the two-layer material.For the phenomenon of insufficient high-frequency sound absorption on the dense materials,the two-layer material formed by the loose material in front and the dense material can exhibit better high-frequency sound-absorbing effect than the single dense material in the same thickness case,and maintains good low-frequency sound absorption performance.