Research On Composite Sound Absorption Structure With Shunt Loudspeaker

With the booming development of industrial production and transportation,the environmental noise problem is becoming more and more serious.How to efficiently absorb low frequency broadband noise is still an urgent problem.Perforated panels and porous materials are the two most commonly used sound absorption structures.Perforated plate has simple structure,high strength,easy processing and production,mainly used for low and medium frequency sound absorption.Porous materials are low-cost,low density,mainly used for high and medium frequency sound absorption.Shunt loudspeaker semi-active sound absorption structure has the advantages of adjustable acoustic impedance,good sound absorption performance,small size and so on.Therefore,this thesis takes the shunt loudspeaker as the basic component,and the classical acoustic structure perforated plate and porous materials are effectively combined,and the proposed composite structure can achieve low and medium frequency broadband sound absorption under the multi-resonance coupling effect.The thesis work provides a design method for the composite structure of shunt loudspeaker sound absorption,which improves the broadband sound absorption ability of shunt loudspeaker and traditional acoustic structure,and provides a new idea for the effective control of low and medium frequency broadband noise in small-scale structures.The main research innovations of this paper are as follows:(1)Based on the semi-phenomenological porous material model,the inversion of the JCA parameters of porous materials was carried out using the experimental data in the impedance tube.The theoretical models of acoustic impedance of the shunt loudspeaker acoustic structure and the perforated plate acoustic structure were derived by the electric-force-acoustic analogy method,respectively.The numerical models of perforated plate and shunt loudspeaker acoustic structures were established,and the mechanism of the influence of shunt loudspeaker parameters on the absorption coefficient was analyzed and experimentally verified.(2)A series-parallel composite structure of shunt loudspeaker and perforated plate(HSLPP)is proposed,and the acoustic impedance theory and numerical model of HSLPP are established based on the electric-force-acoustic analogy method.The acoustic absorption mechanism of HSLPP structure is manifested by the coupled dissipation of acoustic energy in three modes:electric resonance,mechanical resonance and Helmholtz resonance,and the sound loss state of HSLPP at the three resonances is further explained by the complex frequency plane method.The HSLPP structure outperforms the classical microperforated plate and its parallel structure at the same scale,and the experimental results confirm that the HSLPP is a broadband quasiperfect absorber in the range of 200-1100 Hz at more than 2 octaves.(3)A composite acoustic absorption structure(DBSL)consisting of a shunt loudspeaker and a perforated-porous material is proposed,and the acoustic impedance theory and numerical model of DBSL are established based on the dual porosity theory and sound transfer theory.Under the effective coupling effect of the shunt loudspeaker resonance and the thermal viscosity of the porous material,the DBSL structure further broadens the low and middle frequency absorption band range compared with a single porous material layer.In addition,the perforations in the porous material layer are also designed for topological optimization,and the optimized DBSL significantly improves the sound absorption level at resonance.Experimental measurements confirm that the DBSL structure has a broadband and efficient sound absorption capability,and its average absorption coefficient in the frequency band of 100-2000 Hz is greater than 0.86.