Study On The Sound Absorption Characteristics Of Micro-perforated Plate Under Low Perforation Rate

The aperturer of the micro-perforated plate is less than one millimeter.The micro-perforated plate structure is mainly composed of the micro-perforated plate and the cavity behind the plate,it usually has only one sound absorption peak.The resonance frequency and absorption of the structure can be changed by adjusting the structural parameters.Sound coefficient and bandwidth.The micro-perforated plate structure has the characteristics of high sound resistance and low sound quality,and absorbs sound through cavity resonance,thereby eliminating the sound absorbing material in the cavity,simplifying the sound absorbing structure,avoiding environmental pollution,avoiding environmental pollution,low cost,and it can be used in the harsh environment of high temperature,high pressure and high humidity.When the perforation rate of the micro-perforated plate is less than 1.5%,cavity resonance can cause a sound absorption peak,and the vibration of the plate itself can also cause a sound absorption peak.However,most previous studies have ignored the vibration of the plate itself.In order to study the sound absorption characteristics of the micro-perforated plate under the condition of low perforation rate,this paper firstly calculates the natural frequency of the plate with the help of the vibration theory of the thin plate,and compares with the modal analysis results of the finite element software and the experimental results of the sound absorption coefficient.Attempt to equate the vibrating thin plate as a mechanical impedance plate,and give the calculation formula of the sound absorption coefficient of the micro-perforated plate at low perforation rate.In order to improve the low-frequency sound absorption performance of the structure,the mechanical absorption plate and the micro-perforated plate are combined,and the calculation formula of sound absorption coefficient is given.Finally,the sound absorption characteristics of the low-perforation plate are analyzed through theoretical calculations and experiments.According to the theoretical analysis of the sheet resonance,the vibration absorption of the thin plate is equivalent to the mechanical impedance plate resonance absorption.When the plate resonance and the cavity resonance coexist,the mathematical model of the micro-perforated plate is established by the acoustoelectric analogy method and the calculation formula of sound absorption coefficient is given.Firstly,the natural frequency of the sheet is simulated by computer simulation.In the experimental aspect,the natural frequency of the thin plate is measured by the vibration test system,and the experimental measurement results,computer simulation results and the theoretical calculation are consistent.With the help of the standing wave tube test system,the sound absorption coefficient of the micro-perforated plate with lowperforation rate was measured and compared with the theoretical calculation results.The results show that the experimental results are basically consistent with the theoretical calculations.When the perforation rate of the micro-perforated plate is 0.16%,in addition to the sound absorption peak formed by cavity resonance,there is also an obvious sound absorption peak at its natural frequency.In order to improve the low-frequency sound absorption performance of the micro-perforated plate with low perforation rate,it is combined with the mechanical impedance plate as a composite sound-absorbing structure.The transfer matrix of each unit of the composite structure is pushed out by the transfer method,thereby obtaining the total transfer matrix of the entire structure,and finally sound absorption coefficient of the composite structure can be calculated.Using the perforation rate as the experimental variable,the sound absorption characteristics of the micro-perforated plate and the mechanical impedance plate under different porosity conditions were studied,and the vibration acceleration of the two structures was measured using the vibration test system,the results show that When the perforation rate is large,the sound absorption performance of the two structures is mainly determined by cavity resonance.When the perforation rate is low,the micro-perforated plate will produce two sound absorption peaks,which are caused by cavity resonance and plate vibration.The sound absorption coefficient test results are used to try to correct the acoustic impedance of the plate vibration.Compared with the uncorrected results,the corrected results are more consistent with the experimental results.Aiming at the proposed composite sound-absorbing structure,the method of controlling a single variable was used to change the elastic coefficient,damping coefficient,perforation rate and cavity thickness distribution ratio of viscoelastic materials.The sound absorption characteristics of the composite structure were studied using mathematical models.The change rule of the sound absorption curve of the sound absorption peak determines the sound absorption peak influenced by each unit of the composite structure.