Low-Frequency Noise Attenuation In Duct By Mean Of Electro-Acoustic Coupling Method

Low-frequency noise is the difficulty of duct noise control.For traditional reactive silencers,to obtain significant silencing effect at low frequency,the size of the silencer needs to be made very large.Therefore,how to obtain low-frequency broadband silencing effect in a limited volume is the urgent need to solve the problem of pipe noise control.In this paper,a new low-frequency duct noise control method is proposed for the first time by using electro-acoustic coupling mechanism,establishing its mathematical analysis model,designing the structure of the silencer and carrying out experimental research,which can provide a new idea for duct low-frequency noise control.This paper introduces the working principle of the shunt circuit and electroacoustic transducer,and deduces the expression of the sound absorption coefficient under different shunt circuits.The acoustic characteristics of the shunt absorber are summarized,and the effect of the shunt absorber in duct noise control is verified by numerical and finite element methods.Secondly,a low-frequency noise control method based on ultra-fast bypass ducts is proposed by combining the shunt absorber and the Herschel-Quincke tube mechanism.The model for implementing this control method consists of a main pipe and a set of coupled loudspeakers,where the loudspeaker set acts as a noise bypass transmission path,similar to the role of a bypass line in a Herschel-Quincke pipe.The physical model of the silencer is established by the total set parameter method and plane wave assumption,and the working mechanism of the method is analyzed from the perspective of impedance matching,and the acoustic matching characteristics,acoustic transmission law and acoustic reflection effect of the model are obtained.The analytical calculation results and the finite element simulation results were verified each other,and the study showed that the single group model can obtain the noise reduction effect of more than 5d B at the resonance frequency,and has the advantages of small space occupation and adjustable target frequency,etc.On this basis,the acoustic attenuation characteristics of the model under the combination of infinite period and finite period arrays were studied by using the transfer matrix method,and the design method of low-frequency broadband silencer array was formed,and the coupling effect of the resonant silencer band and Bragg band gap of the dual-coupled muffler was analyzed,which showed that the noise reduction of the finite periodic array model could reach 8d B and the logarithmic bandwidth could reach 10.8.Finally,a shunt absorber,a dual-coupled silencer unit and a finite silencer array test rig were designed respectively.Based on the acoustic wave decomposition method,the sound absorption coefficients and their impedance characteristics of the shunt absorber were verified and compared with theoretical calculations and finite element model results.The sound transmission coefficients of the two-loudspeaker coupled sound transmission system were studied experimentally,and the total set of physical parameters of the loudspeakers were calibrated.The transmission loss of the proposed silencer and finite periodic array was measured experimentally by the double loading method.