Influence of Density on Sound Absorption Coefficient of Fibre Board

For acoustic applications such as theaters, cinema halls, auditoriums the data on acoustic properties i.e. sound absorption coefficient and sound transmission loss are required to evaluate the acoustic behavior of panel products and to facilitate the necessary design computations. Fibre boards are widely used in private and commercial buildings, but not much data are available on acoustic efficiency of fibre boards. The study was carried using acoustic pulse tester based on standing wave method for evaluating sound absorption coefficient. Wood fibre boards of different densities ranging from 200 to 800 kg/m3 were taken and their sound absorption coefficients at frequencies ranging from 125 Hz to 4000 Hz were evaluated in third octave band. Noise reduction coefficient of the samples was also computed. From the study, it is observed that low density fibre board possess high sound absorption coefficient and noise reduction coefficient when compared with high density fibre boards. It was seen that sound absorption coefficient increases with decrease in density and vice versa.

Improving the Cellular Characteristics of Aluminum Foam for Maximum Sound Absorption Coefficient Using Genetic Algorithm

Fabricating of metal foams with desired morphological parameters including pore size,porosity and pore opening is possible now using sintering technology.Thus,if it is possible to determine the morphology of metal foam to absorb sound at a given frequency,and then fabricate it through sintering,it is expected to have optimized metal foams for the best sound absorption.Theoretical sound absorption models such as Lu model describe the relationship between morphological parameters and the sound absorption coefficient.In this study,the Lu model was used to optimize the morphological parameters of aluminum metal foam for the best sound absorption coefficient.For this purpose,the Lu model was numerically solved using written codes in MATLAB software.After validating the proposed codes with benchmark data,the genetic algorithm(GA)was applied to optimize the affecting morphological parameters on the sound absorption coefficient.The optimization was carried out for the thicknesses of 5 mm to 40 mm at the sound frequency range of 250 Hz–8000 Hz.The optimized parameters ranged from 50%to 95%for porosity,0.1 mm to 4.5 mm for pore size,and 0.07 mm to 0.6 mm for pore opening size.The result of this study was applied to fabricate the desired aluminum metal foams for the best sound absorption.The novel approach applied in this study,is expected to be successfully applied in for best sound absorption in desired frequencies.

Sound absorption property of wood for five eucalypt species

The sound absorption coefficients of wood and wood boards for five eucalypt species (Eucalyptus urophylla, Euca-lyptus urophylla E. grandis, Eucalyptus urophylla E. tereticornis, Eucalyptus urophylla E. camaldulensis and Eucalyptus cloeziana) that were collected from plantation in Dongmen Forestry Center of Guangxi Province, China were tested with stand-ing wave method and their sound absorption properties were also compared. The results showed that the sound absorption co-efficients of the five eucalypt wood species did not change evidently below 1000 Hz, but above 1000 Hz their sound absorption coefficients increased with the increasing frequency. The difference in sound absorption coefficient among five species of eucalypt wood is not evident at the tested frequency range (200-2000 Hz), but the sound absorption property of Eucalyptus urophylla at low frequency is better than that of other four species. The sound absorption coefficient of the tangential-sawn board is higher than that of the radial-sawn board. The sound absorption property of eucalypt wood of 0.5 cm in thickness is much better than that of 1.0 cm in thickness. It is concluded that wood sound absorption properties of eucalypts are affected by their board thickness and the type of sawn timber within the testing frequency, but the variance of wood sound absorption property among the five tested species is not significant.

Development of a High Sound Absorption Material CEMCOM

Based on sound absorption mechanism of material,the special sound absorption material CEMCOM for road sound insulation is introduced.This high sound absorption material is mainly composed of expanded perlite.Using multiple sound absorption structure can improve sound absorption property of material.According to the preparation principle and durability design of material,a new kind of material with low cost and high durability is developed.

Sound absorption property of open-pore aluminum foams

This paper presents a study on sound absorption property of aluminum foam by evaluating its sound absorption coefficients using standing wave tube method. Experimental results showed that the average values of sound absorption coefficients (over the test frequency range) are all above 0.4, which indicate very good sound absorption property of the aluminum foams. The sound absorption coefficient is affected by frequency and pore structure, and reaches its maximum value at around 1 000 Hz. With the increase of porosity and decrease of cell diameter, the sound absorption coefficient values increase.

Optimization of Sound Absorption and Insulation Performances of a Dual-Cavity Resonant Micro-Perforated Plate

This study investigates a dual-cavity resonant composite sound-absorbing structure based on a micro-perforated plate.Using the COMSOL impedance tube model,the effects of various structural parameters on sound absorption and sound insulation performances are analyzed.Results show that the aperture of the micro-perforated plate has the greatest influence on the sound absorption coefficient;the smaller the aperture,the greater is this coefficient.The thickness of the resonance plate has the most significant influence on the sound insulation and resonance frequency;the greater the thickness,the wider the frequency domain in which sound insulation is obtained.In addition,the effect of filling the structural cavity with porous foam ceramics has been studied,and it has been found that the porosity and thickness of the porous material have a significant effect on the sound absorption coefficient and sound insulation,while the pore size exhibits a limited influence.

Improving the Sound Absorption Properties of Flexible Polyurethane (PU) Foam using Nanofibers and Nanoparticles

Polyurethane foam as the most well-known absorbent materials has a suitable absorption coefficient only within a limited frequency range.The aim of this study was to improve the sound absorption coefficient of flexible polyurethane(PU)foam within the range of various frequencies using clay nanoparticles,polyacrylonitrile nanofibers,and polyvinylidene fluoride nanofibers.The response surface method was used to determine the effect of addition of nanofibers of PAN and PVDF,addition of clay nanoparticles,absorbent thickness,and air gap on the sound absorption coefficient of flexible polyurethane foam(PU)across different frequency ranges.The absorption coefficient of the samples was measured using Impedance Tubes device.Nano clay at low thicknesses as well as polyacrylonitrile nanofibers and polyvinyl fluoride nanofibers at higher thicknesses had a greater positive effect on absorption coefficient.The mean sound absorption coefficient in the composite with the highest absorption coefficient at middle and high frequencies was 0.798 and 0.75,respectively.In comparison with pure polyurethane foam with the same thickness and air gap,these values were 2.22 times at the middle frequencies and 1.47 times at high frequencies,respectively.Surface porosity rose with increasing nano clay,but decreased with increasing polyacrylonitrile nanofibers and polyvinyl fluoride nanofibers.The results indicated that the absorption coefficient was elevated with increasing the thickness and air gap.This study suggests that the use of a combination of nanoparticles and nanofibers can enhance the acoustic properties of flexible polyurethane foam.

Sound absorption property of open-pore aluminum foams

The sound absorption property of aluminum foam was studied by testing its sound absorption coefficients using standing wave tube method. The open-pore aluminum foams were prepared by infiltration process, with pore size of 0.5 mm to 3.2 mm and porosity of 54.2% to 77%. The frequency of indicted sound wave was ranging from 125 Hz to 10 kHz. The results show that the average values of sound absorption coefficients are all over 0.4 and the aluminum foam has better sound absorption property, its coefficients is influenced by frequency and pore structure, and reaches the maximum at about 1 kHz, with increasing porosity and decreasing cell diameter the sound absorption coefficient values increase.

Determination of the Sound Absorption Capacity of Hydraulic Concrete Mixtures Added with Waste Tire Rubber

There are different types of pollutants that are harmful to the environment, including smog, chemicals that are dumped into rivers, scrap tires, etc. The latter have the particularity that it is not possible to recycle them to manufacture new tires. In the present work, hydraulic concrete plates added with waste tire rubber were manufactured to modify their sound absorption capacity. It was found that the rubber additions produce changes in the density of the material and in the sound absorption capacity. When the material is exposed to high-frequency sounds that correspond to high-pitched sounds, its absorption capacity increases. On the contrary, when the test frequency is low, that is, bass sounds, the sound absorption capacity decreases. The results obtained in this work suggest that the proposed mixtures are suitable for the possible manufacture of acoustic insulating shields.

Application of Response Surface Methodology to Optimize the Preparation of Rubber Foam Composite as Sound-Absorbing Material Using Scrap Rubber Powder

In this paper, scrap rubber powder(SRP), azodicarbonamide(ADC) as foaming agent and double-component epoxy resins(ER) as binder were used to prepare porous sound-absorbing material of rubber foam composite(RFC) by hot-pressing process. Response surface methodology(RSM) was employed to evaluate three process variables, i e, specimen thickness(A), ADC dosage(B) and foaming temperature(C), and to establish two polynomial function model equation between sound absorption coefficient(α) and three process factors(A, B, C) at middle and low frequency 250 Hz, 500 Hz, 800 Hz, 1 000 Hz to determine the optimal preparation condition of RFC. The statistical analysis of results demonstrated that specimen thickness(A) exerted significant impact on sound absorption properties of RFC. And the optimum prepared condition of RFC was 10 mm specimen thickness, 3.00 g ADC dosage, and approximately 196 ℃ foaming temperature. Under optimal condition, sound absorption coefficient of RFC could reach 5.68%(250 Hz), 7.67%(500 Hz), 20.73%(800 Hz), 18.71%(1 000 Hz), coinciding with the predicted values 5.70%(250 Hz), 7.69%(500 Hz), 20.77%(800 Hz), 18.74%(1 000 Hz) from the predicted polynomial function model, which exhibited that RSM could be used to optimize the preparation process of sound-absorbing materials.

Theoretical Calculation and Analysis of Muffler Based on Multilayer Sound Absorbing Material

The multilayer impedance composite sound absorption structure of the new muffler is proposed by combining the microporous plate structure with the resonant sound absorption structure of the porous material.Firstly,the acoustic impedance and acoustic absorption coefficient of the new muffler structure are calculated by acoustic electric analogy method,and then the noise attenuation is calculated.When the new muffler structure parameters change,the relationship among the noise frequency,the sound absorption coefficient and the noise attenuation is calculated by using MATLAB.Finally,the calculated results are compared with the experimental data to verify the correctness of the theoretical calculation.The variation of resonance peak,resonance frequency and attenuation band width of each structural parameter is analyzed by the relation curve.The conclusion shows that it is feasible to use multilayer sound absorbing materials as the body structure of the new muffler.And the influence relationship between the change of various parameters of the sound absorption structure with the sound absorption coefficient and noise attenuation is obtained.

Sound Character Calculation and Analysis of Sound Barrier Based on Acoustoelectric Analogy

A new acoustic barrier structure with resonant sound of micro-perforation board absorption structure and impedance composite sound-absorption structure is proposed.The acoustic impedance and the sound-absorption coefficient of the acoustic structure are calculated via means of equivalent circuit.MATLAB is used to calculate the relationship between the parameters of the ontology structure and the sound-absorption coefficient and the sound insulation.It is revealed that the sound barrier of the new ontology structure is 7.659.80 dB,which is more than the sound barrier of the traditional reflective structures.The relationships among the parameters of sound-absorption structure,sound-absorption coefficient,and sound insulation performance are obtained.In addition,the parameters can be transformed to satisfy the noise reduction requirements of various road sections,which has a admirable adaptability.The acoustic barrier can have tremendous acoustic performance only if there is a splendid sound insulation in the traffic noise frequency band.

压电复合材料梯度分布声学特性研究

目前,压电复合材料在吸声降噪领域应用广泛,但其低频吸声性能并不理想。为解决此问题,以0-3型压电复合材料为研究对象,提出使压电陶瓷体积含量呈梯度分布以提高其低频吸声系数的方法。首先,基于声电类比法和传递矩阵法,推导多梯度分布的理论公式,并通过文献构型对其进行验证;其次,将均匀分布与梯度分布的吸声系数进行比较,发现梯度分布会改变材料的声阻抗,从而改变吸声系数。最后,进行梯度分布压电复合材料数值分析,结果表明,同等条件下,当压电陶瓷体积含量呈梯度递减,且梯度差和第一梯度的厚度增加时,可明显提高低频吸声系数。

基于阻抗匹配的吸声方法

对于低中频声波入射,采用主动吸声方法可以获得较好的吸收性能,而对于高频声波入射则不能达到很好的吸收性能,为此,又提出了通过调节吸声材料后扬声器的表面阻抗来改变吸声系数的半主动吸声方法。将可控扬声器置于吸声材料后面,调节其表面阻抗,使其与空气的声阻抗达到最佳匹配,从而实现对吸声性能的有效调控。实验结果表明:半主动吸声方法可以在不断改变入射声波频率情况下对吸声系数进行有效调整,使吸声系数始终处于最大值。

船用厨余管道包覆材料吸隔声性能试验研究

根据某远洋客船舱室部分厨余管道的案例,试验针对包覆材料和粘接剂研究吸声系数和隔声量在中低频范围内的变化规律,讨论船用厨余管道包覆材料厚度和粘接剂种类选取对吸隔声性能的影响。对比分析发现材料厚度从19 mm提升至25 mm时,吸隔声性能提升最为显著,吸声系数提升约143%,隔声量提升约27%。研究结论为船用厨余管道的安装及材料应用提供一定的技术参考。

变截面消声管道耦合Helmholtz腔结构的声学性能

基于局域共振理论与管道消声理论,设计了一种变截面消声管道耦合Helmholtz谐振腔的声学超材料结构,并运用COMSOL软件进行仿真研究.在此基础上,探讨了变截面声学超材料结构的几何参数对吸声系数峰值的影响,运用声学试验测试了该声学超材料结构的声学性能.结果表明:该变截面声学超材料结构在低频范围(200~600 Hz)内可实现良好的吸声效果;通过改变管道小孔的截面半径,可以实现声学超材料结构固有频率的定向调节;与普通Helmholtz腔相比,该声学超材料结构的吸声系数峰可在一定低频范围内移动,提高了结构在低频范围内的吸声效果,拓宽了吸声系数峰值对应频率的范围;声学超材料结构的几何参数得到了优化,具有良好的吸声效果.

道路声屏障组合吸声结构设计与评估

声屏障在道路交通噪声污染防治中得到了广泛应用,但同时面临材料吸声性能有限、轻量化程度有待提升等问题。为了更好地提升道路声屏障的降噪效果,需要研究组合吸声结构的声学性能及其影响因素。建立了二维阻抗管有限元模型,与实验数据进行对比验证了其可靠性。基于有限元仿真构建了微穿孔板-双层多孔吸声材料-空腔组合吸声结构,研究了几何参数对组合结构的吸声性能的影响,并在实际道路场景中进行了仿真分析。结果表明,微穿孔板的孔径和厚度减小,组合结构在中高频段的吸声效果提升;穿孔率减小,组合结构在低频段的吸声性能提升,但是中高频吸声性能显著降低;多孔吸声材料厚度的增加能提升组合结构中高频吸声系数。在多孔吸声材料背后合理设置空腔并不会降低组合结构的声学性能。穿孔率3%,孔径0.4 mm,板厚1 mm的微穿孔板与3 cm聚酯纤维+3 cm三聚氰胺+2 cm空腔的组合吸声结构降噪效果较好,将其作为吸声型声屏障的材料。吸声型和隔声型声屏障插入损失的规律基本一致,采用组合吸声结构的吸声型声屏障较隔声型声屏障插入损失提升1~2 dB,能够较好地控制中低频交通噪声,具有实际工程价值。

人工漂珠制备吸声材料的降噪性能研究

中低频噪音污染已是影响人类身心健康的重要环境污染之一,开发中低频吸声系数高、制造成本低的吸声材料一直以来都是降噪行业的重要目标。人工漂珠(简称漂珠)既可以通过收集矿石开采后废弃的小颗粒矿砂获得,又可以通过粉碎矿石形成所需粒径的矿砂,然后再经矿砂预热、煅烧等工艺获得。其表面和内部具有大量孔隙,因而具备潜在的吸声性能,但其用作吸声材料的潜力尚未得到充分的探索。本工作旨在探讨由漂珠制成的吸声材料的吸声性能。采用不同粒径搭配不同用量的漂珠和粘合剂制备四种吸声材料样品,对其微观形貌进行表征,统计孔隙面积分布,并用阻抗管测量四种材料的吸声系数。结果表明,在本工作所涉及的参数范围内,四种吸声材料在400~1000 Hz频率上均可有效吸收噪声(吸声系数大于0.2)。随着粒径小、孔隙小的漂珠用量的增加,漂珠制备的材料的吸声能力逐步增强,主要是由于孔隙的减小延长了声波在材料内部的传播路径。此外,不同粒径搭配不同漂珠用量还会影响材料吸声系数峰值所对应的频率;换言之,可以通过漂珠配比的针对性设计,加强吸声材料对某一给定频率噪声的敏感度。本研究可为开发以漂珠为主要成分的低成本吸声材料提供新的思路。

开孔泡沫铝无规则入射的吸声性能研究

通过混响室对不同厚度的开孔泡沫铝在不同背腔深度下的吸声性能进行测试,获得了不同厚度的泡沫铝板在不同腔深下的吸声系数。研究表明在频率低于630 Hz时,不同厚度泡沫铝板的吸声系数随着背腔深度的增加逐渐提高。在630~5 000 Hz频率范围内,当泡沫铝材料的厚度大于4 mm,背腔深度大于40 mm时,不同厚度泡沫铝板的吸声系数均大于0.6。计算了不同厚度的开孔泡沫铝材料在不同背腔条件下的降噪系数,为泡沫铝材料的实际工程应用提供参数选择。

基于人工神经网络的共振吸声超材料声学性能快速预测及结构优化设计

针对共振吸声超材料声学性能快速预测及结构优化设计需求,提出了一种基于人工神经网络的共振吸声超材料性能预测方法.首先,建立了由微穿孔板和Helmholtz共振腔组成的多层穿孔型共振吸声超材料的理论模型,并通过仿真与实验验证其正确性;随后,通过理论模型生成数据集,并以此为基础,采用BP(back propagation)神经网络原理,搭建了结构特征参量与声学性能的人工神经网络模型;之后,将训练后的人工神经网络模型与遗传算法相结合,对共振吸声超材料进行声学性能最优化设计.结果表明:训练后的人工神经网络模型可以对目标结构的吸声性能进行准确预测,并且预测效率相较理论模型提高50%以上;人工神经网络模型与优化算法的结合不仅能提高优化效率,优化后的结构也具有良好的低频宽带吸声性能.人工神经网络为大规模结构性能预测计算提供了便利,在超材料等结构设计及优化领域具有广阔的应用前景.