A Study On Diffusion Properties Of The Quadratic Residue Diffuser Structure Composited With Micro-perforated Or Perforated Plate

With the economic and social development, environmental pollution isgenerated.Noise pollution, as an environmental pollution, with water pollution, airpollution is seen as three major global environmental issues, has gradually become amajor hazard to human beings. Noise can cause people become upset and has become amajor nuisance in contemporary society. Currently noise pollution control is mainlyrelying on engineering controls, which included design and install the sound insulationacoustic structure, to reduce or eliminate noise pollution hazards. Followed, variousacoustic characteristics of the acoustic structure is become a hot research direction,which has very important significance.Currently the acoustic properties of the acoustic structure include three directions,sound absorbing structure with the purpose to improve the sound absorption performance,sound insulation struture which is designed to improve the sound insulation properties,diffusion structure with the purpose to improve the diffusion properties. The singleacoustic performances of one structure have been studied very much.So one structurewith two or more properties is current research trends. The combination of soundabsorption and diffusion properties have been studied in foreign countries, but in ourcountry relative research has seldom been reported.This paper is focuses on quadratic residue diffuser (QRD) and its composited structurewith micro-perforated or perforated panels, including diffusion properties of quadraticresidue diffuser (QRD), diffusion properties of QRD composite structure withmicro-perforated plate, diffusion properties of QRD composite structure with perforatedplate and the diffusion properties of composite structures when the sound source incidentat different angles.The research of quadratic residue diffusers structure (QRD)mainly about theproperties of one-dimensional N=7QRD diffuser structure in accordance with standarddiffusion test method, then obtained a series of reflections polar and diffusioncoefficients graphs by calculating, finally get some results as follow, QRD structure has a good diffusion property, the diffusion coefficient between100Hz to500Hz band canreach0.85to0.95, and the low-frequency diffusion performance is very good.The research about composite structure with micro-perforated plate is at the basic offormer research and composite different thicknesses or perforation rate micro-perforatedaluminum plate structure, including micro-perforated plate thickness of0.6mm,0.7mm,0.8mm, perforation rate of1%,2%,3%, and according to the standard test method, wecan get a series of reflected sound energy polar diagrams and diffusion coefficient graphsby cauculating, finally by analysis we can concluded that micro-perforated platecomposite structure especially in low frequency can still maintain good diffusionproperties of QRD structure, diffusion coefficient in the low frequency can reach0.8ormore, and studies have shown that because of the micro-perforated plate’ssound-absorbing performance the reflected sound of composite structures can reduceabout5dB, the composite structure have both sound absorption and diffusion performancein the low-frequency. Meanwhile,0.8mm-2%composite structure have the best diffusionproperties among the nine kinds of micro-perforated plate composite structure,which havethe a average diffusion coefficient of0.65.The research about composite structure with perforated plate is similar to themicro-perforated plate composite structure, which including perforated plate structurewith thickness of1mm,2mm, and3mm, perforation rate of3%,5%, and8%. Make testaccording to the standard method, get reflected sound energy polar diagram and thediffusion coefficient graph by calculating, and finally drawn a series of the conclusions asbelow. Composite structure with perforated plate can maintained sound diffusionproperties in the low frequency，between160Hz to800Hz its diffusion coefficient canreached0.85or more, and studies have shown that because of the perforated plate’ssound-absorbing performance the reflected sound of composite structures can reduceabout3dB, the composite structure have both sound absorption and diffusion performancein the low-frequency. Meanwhile,2mm-5%composite structure have the best diffusionproperties among the nine kinds of perforated plate composite structure,which have the aaverage diffusion coefficient of0.72.The diffusion properties of composite structure in different sound incidence angleincluding0.8mm2%micro-perforated plate composite structure and2mm5%perforatedplate composite structure at sound incidence angle of10degrees,20degrees,30degrees.By test and cauculate we can concluded that, the diffusion properties of the compositestructure decreases with the increase of the sound incident angle,and the test results aresymmetrical in both sides when at a same sound incident angle. The received acousticenergy become smaller in the sound incident side because of the offset of the incident anddiffuse sound, and become larger in the other side due to the superposition of the reflectedand diffuse sound.