High Sound Absorption Coefficient Research Articles

Comparative Study of Sound Absorption Coefficients of Coir/Kenaf/Sugarcane Bagasse Fiber Reinforced Epoxy Composites

This research focuses on the sound absorption coefficient of three different natural fibers reinforced epoxy composites. The natural fibers used are coconut coir, kenaf, and sugarcane bagasse. All of these fibers were mixed with epoxy resin and hardener with a ratio of 4:1. The mixtures were then poured into a circular mold and compressed by using compression molding technique. It was left for curing for 24 hours at standard room temperature. The results were obtained using the two-microphone transfer functions impedance tube method according to ASTM E1050-12. It is found that as the fiber loading increased, the sound absorption coefficient of the composites increased. 20wt% Coconut coir epoxy composites and 20wt% kenaf fiber epoxy composites have the highest sound absorption coefficient with almost similar sound absorption of 0.078 at 5000Hz. While, 20wt% sugarcane bagasse epoxy composites have sound absorption of 0.075 at 5000Hz.

Effect of high molecular weight isocyanate contents on manufacturing polyurethane foams for improved sound absorption coefficient

Noises generated in automobile compartments can be controlled by utilizing sound absorption and insulation materials such as polyurethane foams. Polyurethane foams are synthesized by varying polymeric methylene diphenyl diisocyanate (MDI) content for exploring the effect of high functional isocyanate on cellular and acoustic properties. The use of polymeric MDI affects polyurethane matrix modulus and drainage flow rate of the foams, and it also has strong effects on cell structure and air flow resistance (AFR). The highest sound absorption coefficient is achieved at the optimum amount of the polymeric MDI. Therefore, the optimum amount of polymeric MDI content is recommended to achieve not only high sound absorption coefficient but also high transmission loss from the polyurethane foams.

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.

Physical Properties of Eco-friendly Kenaf Fiber Imbedded Nonwoven for Automotive Pillar Trim

This study investigated the physical properties including the sound absorption property of Kenaf natural fiber imbedded nonwoven for automotive pillar trim. Seven kinds of Kenaf imbedded nonwoven specimens mixed with polypropylene and low melting PET fibers were prepared through needle punching nonwoven process. Physical properties such as air permeability, water absorption, sound absorption coefficient, and porosity were measured and compared with different processing factors of needle punching nonwoven. High blend percentage of low melt PET fibers made pore size lower and smaller, which resulted in low air permeability and water absorption. Sound absorption coefficient of nonwoven specimen was highly dependent upon weight and thickness of the nonwoven and correlation coefficient was above 0.83, respectively. It was also affected by pore diameter, i.e. low pore sized nonwoven showed high sound absorption coefficient, which was caused by the high needle depth and high blend ratio of low melt PET.

Experimental study on the sound absorption characteristics of continuously graded phononic crystals

Novel three-dimensional (3D) continuously graded phononic crystals (CGPCs) have been designed, and fabricated by 3D printing. Each of the CGPCs is an entity instead of a combination of several other samples, and the porosity distribution of the CGPC along the incident direction is nearly linear. The sound absorption characteristics of CGPCs were experimentally investigated and compared with those of uniform phononic crystals (UPCs) and discretely stepped phononic crystals (DSPCs). Experimental results show that CGPCs demonstrate excellent sound absorption performance because of their continuously graded structures. CGPCs have higher sound absorption coefficients in the large frequency range and more sound absorption coefficient peaks in a specific frequency range than UPCs and DSPCs. In particular, the sound absorption coefficients of the CGPC with a porosity of 0.6 and thickness of 30 mm are higher than 0.56 when the frequency is 1350–6300 Hz and are all higher than 0.2 in the studied frequency range (1000–6300 Hz). CGPCs are expected to have potential application in noise control, especially in the broad frequency and low-frequency ranges.

Effect of membranes at microscopic polygonal faces of polyurethane foam by using homogenization method

Sound absorption coefficient in poroelastic media depends on the geometries in the microscopic scale. In some polyurethane foams that exhibit high sound absorption coefficients in the middle frequency range around 1 kHz, the faces of polygonal shape of microscopic structure are covered by thin membranes. Moreover, a hole is frequently found in some membranes. This type of microscopic structure is considered to contribute to the high sound absorption performance. Multi-scale analysis for sound-absorbing poroelastic media with periodic microscopic geometries has been recently proposed by one of the authors. In this method, the homogenization method based on the asymptotic expansions are utilized and further extended to express the viscous dissipation in the vicinity of the boundary between the solid and fluid phases, thermal dissipation from the fluid phase to the solid phase. Analysis in the microscopic scale is first performed by using a unit cell of the periodic structure and macroscopic properties are derived. The properties are then applied to calculate macroscopic response such as sound absorption coefficient. In this paper, we apply this multi-scale analysis and investigate numerically the relationship between the size of the hole in membranes and sound absorption performance.

An integrated experimental and computational approach to material selection for sound proof thermally insulted enclosure of a power generation system

Sound proof canopies for diesel power generators are fabricated with a layer of sound absorbing material applied to all the inner walls. The physical properties of the majority of commercially available sound proofing materials reveal that a material with high sound absorption coefficient has very low thermal conductivity. Consequently a good sound absorbing material is also a good heat insulator. In this research it has been found through various experiments that ordinary sound proofing materials tend to rise the inside temperature of sound proof enclosure in certain turbo engines by capturing the heat produced by engine and not allowing it to be transferred to atmosphere. The same phenomenon is studied by creating a finite element model of the sound proof enclosure and performing a steady state and transient thermal analysis. The prospects of using aluminium foam as sound proofing material has been studied and it is found that inside temperature of sound proof enclosure can be cut down to safe working temperature of power generator engine without compromise on sound proofing.

振動増幅による圧電吸音板の吸音特性の広帯域化

This paper describes an improvement method of the sound absorption effect for the piezoelectric sound absorbing panel. The piezoelectric sound absorbing panel has a high sound absorption coefficient at around the natural frequency of the fundamental vibration mode of the panel. However, the effective bandwidth is narrow because the sound absorption coefficient depends on the amplitude of the vibration of the panel. To solve this problem, we propose a resonance amplification method for the panel. The resonance of the panel is amplified by adding force to the panel using another piezoelectric elements in this method. The added force must be proportional to the sound pressure at the left-hand surface of the panel. Because this method requires a large value of an equivalent stiffness ratio of the piezoelectric element that enhances the equivalent stiffness ratio is also used in this method. The governing equations were theoretically derived, and the optimum values of the LR circuit were formulated. The effectiveness of this method was verified through simulations and experiments.

UTILIZATION OF OIL PALM TRUNK (ELAEIS GUINEENSIS) AS FOAM COMPOSITE FOR SOUND ABSORPTION

Oil Palm Trunk (OPT) act as a filler for polymer foam composite has been investigated and proved to have ability to absorb sound. In this study, treatment of wood untreated and treated with acid hydrolysis named as UP5 and TP5 was use as filler. This study was developed to compare the ability of sound absorption based on different composition of filler in polymer foam composite. By choosing the size of <500 µm, three different percentage has been selected which is 10 %, 15 % and 20 % for both conditions. These samples has been tested by using Impedance Tube test according to ASTM E-1050 for sound absorption coefficient, α measurement and Scanning Electron Microscopy (SEM) for determine the porosity for each samples. 20 % filler loading of UP5 gives highest sound absorption coefficient of 0.97 at 4728 Hz. Meanwhile for 20 % loaded of TP5 gives 0.99 at 3371 Hz. When comparing the sound absorption coefficient for both sounds absorbing materials, TP5 polymer foam composite showed higher value of sound absorption coefficient, α at lower frequency level (Hz) as compared to UP5 polymer foam composite which gives better results in sound absorption.

A Compound Micro-perforated Panel Sound Absorber with Partitioned Cavities of Different Depths

The micro-perforated panel (MPP) sound absorber is becoming a good replacement of conventional porous absorbers in building noise control. The MPP absorber is fiber-free and avoids potential harms such as powdered fibers and damage to the person's health. This paper presents a new compound MPP sound absorber architecture with excellent sound absorption performance both on higher sound absorption coefficient and broader absorption band compared with single MPP absorber. The absorber consists of an array of parallel-arranged MPP sub-absorbers with different depths, where different local resonances are apparent and dominate. In this paper, firstly, an analytical method is proposed to look into the mechanism of the absorber architecture design and this method is validated through simulations based on a finite element procedure. Secondly, the acoustic properties from different MPP absorber dimension sets are investigated through simulations with the proposed theoretical method. Results show that the presented MPP absorber can have normal incidence sound absorption coefficients higher than 0.5 over the frequencies from 370Hz to 2520Hz, with maximum value of 0.9. This indicates that the proposed MPP absorber provides a good alternative for indoor sound absorption applications in commercial and industrial buildings.

Synthesis of polyimide cross-linked silica aerogels with good acoustic performance

Polyimide cross-linked silica gels with different weight percentages of solid precursors and different volumes of MTMS were prepared by using bis(trimethoxysilylpropyl)amine (BTMSPA) cross-linked polyamide acid, synthesized by 4,4′-oxydianiline (ODA), p-phenylenediamine (PPDA) and biphenyl-3,3′,4,4′-tetracarboxylic dianhydride (BPDA), compounding with a silica network which was hydrolysed by MTMS, then supercritically dried to produce a hybrid aerogel. The obtained aerogels exhibit striking properties such as low density (as low as 90 mg cm−3), a large surface area (up to 582 m2 g−1), lower shrinkage (up to 20%) and are more easily accessible than those previous reported. Formulations made of 8.7% and 11.72% solid precursors never collapsed under compression. Furthermore, the latter shows the maximum modulus (up to 17 MPa) and a higher sound absorption coefficient (more than 0.8) with a thickness of 3 cm in a specific range of frequencies.

Application of electrospinning fibres on sound absorption in low and medium frequency range

Owing to their excellent viscoelasticity and easy processing properties, polymer materials have a huge potential in sound absorption. Moreover, micro-/nanofibres can be produced by electrospinning technology with many special advantages, such as high specific surface area. In this paper, electrospun fibres based on polyacrylonitrile (PAN), thermoplastic polyurethane (TPU) and thermoplastic polyester elastomer (TPEE) were prepared for the sound absorption test. The scanning electron microscopy micrographs showed that three types of fibres with mean diameters of 400, 1000 and 1000 nm for PAN, TPU and TPEE were obtained respectively. The sound absorption coefficients of the electrospun fibres were measured using the impedance tube instrument at different frequencies. Membranes with different back cavities were investigated. The results showed on the whole that the electrospun fibres had good acoustical performance in the low and medium frequency range (100–2500 Hz). Compared with TPU and TPEE fibre membranes, the PAN membrane measurement at the same condition had higher sound absorption coefficients in the frequency of 100–2500 Hz. These high specific surface and flexible electrospun fibres are suitable candidates for noise reduction in the low and medium frequency range.

Utilization of Treated Red Meranti Wood Dust as Polymer Foam Composite for Acoustic Study

A Red Meranti Wood Dust (RMD) act as a filler for polymer foam composite has been investigated and proved to have ability to absorb sound. In this study, treatment of wood dust with and without acid hydrolysis named as WDB and WDA respectively was use as filler. This study was developed to compare the ability of sound absorption based on treated filler and particle size of wood dust. By choosing the size of 355 μm, three different percentage has been selected which is 10%, 15% and 20% for both conditions. These samples has been tested by using Impedance Tube test according to ASTM E-1050 for sound absorption coefficient, α measurement and Scanning Electron Microscopy (SEM) for determine the porosity for each samples. 10% loaded of WDB as filler gives highest sound absorption coefficient of 0.999 at 4015.63 Hz. Meanwhile for 20% loaded of WDA gives 0.997 at 3228.13 Hz. When comparing the sound absorption coefficient for both sounds absorbing materials, WDB-polymer foam composite RMD showed higher value of sound absorption coefficient, α at higher frequency as compared to WDA-polymer foam composite.

Experimental study of wood acoustic absorption characteristics

Abstract The objective of this study was to determine normal impedance on the surface as well as sound absorption coefficients for several wood species from Europe and from the tropical zone. The mathematical models of Miki, Attenborough, and Allard – dealing with acoustic properties of porous materials – have also been compared. The air flow resistivity exhibits a distinct link between fiber dimensions and wood porosity. The highest sound absorption coefficient was found for oak, ash, sapeli, and pine woods at 2 kHz frequency. The Attenborough model provides results closest to laboratory measurements, although it still requires significant improvements. The Miki and Allard models have some drawbacks and should be applied with reservation for the determination of wood acoustic properties.

J045073 圧電吸音板のLR回路による周波数調整([J045-07]知的材料・構造システム(7))

This paper proposes a frequency tuning method of the piezoelectric sound absorbing panel. The piezoelectric elements on the panel shunted with an inductance and a resistance work like a dynamic vibration absorber. The sound absorbing panel transforms sound energy into the vibration energy, and this vibration energy is dissipated through the resistance using electrical resonance. Because the piezoelectric sound absorbing panel has high sound absorption coefficient around its natural frequency, this method can be used for low-frequency noise reduction. However, the frequency at which the sound absorption coefficient becomes 1 was automatically determined in the method proposed in the previous research. Therefore, this paper proposes the frequency tuning method of the piezoelectric sound absorbing panel using the LR circuit. The governing equations were theoretically derived, and the optimum values of the LR circuit were formulated. Theoretical analysis was validated through simulations and experiments.

Thermal and acoustic properties of aluminium foams manufactured by the infiltration process

Metallic foams can be classified into closed-cell and open-cell foams depending on the connectivity between the cells. Currently, the majority of metallic foams on the market are closed-cell aluminium foams. However, open-cell aluminium foams are more appropriate for some applications. In this work, we analyze the thermal and acoustic properties, sound absorption coefficient at normal incidence and static flow resistivity of aluminium foams manufactured by means of the infiltration process. We have produced aluminium foams with similar porosity but with three different cell diameters: 0.5, 1 and 2mm. The results reveal the important role of the cell diameter in fixing the physical properties of these materials. The foams manufactured by the infiltration technique are characterized by a highly homogeneous structure and by a high sound absorption coefficient at low frequencies when they are backed by an air gap. Specifically, its thermal and acoustic properties make the 0.5mm cell diameter aluminium foam a good candidate for applications in the construction sector, for example.

Application Prospect of Basalt Fabrics Wall Material

Functions of the wall and some of wall materials are introduced. Basalt filaments possess excellent properties with high strength, high temperature resistance, corrosion resistance, small hygroscopicity, small thermal conductivity and high sound absorption coefficient. High performance basalt fabrics can be gelatinized into compound cementitious materials with cement or gypsum. The performance of basalt compound boards mainly rely on the performance of basalt filaments. So basalt compound boards possess excellent characteristics with light-weight, high strength, fire prevention, sound insulation and heat preservation. It is green initiative and easy construction as new wall materials. Basalt compound cementitious materials possess good application prospect in the wall materials along with the development of production technology.

Phononic glass: A robust acoustic-absorption material

In order to achieve strong wide band acoustic absorption under high hydrostatic pressure, an interpenetrating network structure is introduced into the locally resonant phononic crystal to fabricate a type of phononic composite material called "phononic glass." Underwater acoustic absorption coefficient measurements show that the material owns high underwater sound absorption coefficients over 0.9 in 12-30 kHz. Moreover, the quasi-static compressive behavior shows that the phononic glass has a compressive strength over 5 MPa which is crucial for underwater applications.

Investigation on sound absorption properties for recycled fibrous materials

Acoustic is currently one of the most important fields of study. Recently, many studies have been carried out in this field and new findings have uncovered the potential use of new materials for sound absorption applications. This paper investigated the sound absorption properties for recycled fibrous materials including natural fibers, synthetic fibers and agricultural lignocellulosic fibers. Nonwovens produced from recycled natural fibers blended with synthetic fibers have been tested acoustically. Also, biocomposites from agriculture wastes such as rice straw and sawdust have been investigated. The results indicated that nonwoven samples have high sound absorption coefficients at high frequencies (2000–6300 Hz), low sound absorption coefficients at low frequencies (100–400 Hz) and better sound absorption coefficients at mid (500–1600 Hz) frequencies. The sound absorption coefficients at all frequency ranges improved by increasing the thickness of nonwovens. Also, adding air space behind the sample improved the sound absorption at low and mid frequencies. The tested rice straw and sawdust composite samples achieved low sound absorption at low and mid frequencies. However, they have slightly high sound absorption at high frequencies. A significant improvement in sound absorbing performance at low, mid and high frequencies was achieved by adding perforation of 6% for the tested sample and increasing the thickness of nonwoven samples. Adding air spaces behind the tested composite systems could improve the sound absorption at low and mid frequencies. Generally, the results indicated that recycled fibrous materials hold promise for use as raw material for sound absorbing, being low cost, lightweight and biodegradability.

Sound absorption capability and mechanical properties of a composite rice hull and sawdust board

Rice hull–sawdust composite boards were manufactured for sound-absorbing boards in construction. The manufacturing parameters were target density (400, 500, 600, and 700 kg/m3) and rice hull content as percent weight of rice hull/sawdust/phenol resin (10/80/10, 20/70/10, 30/60/10, and 40/50/10). Commercial gypsum board and fiberboard were also used as comparative sound-absorbing materials. The average modulus of rupture (MOR) of the board with a density of 700 kg/m3 and rice hull mixing ratio of 10% was 8.6 MPa, and that of the board with a 400 kg/m3 board density and a rice hull mixing ratio of 40% was 2.2 MPa. The MOR increased with increasing board density or decreasing rice hull mixing ratio. The sound absorption coefficients of some boards (400 kg/m3 and 10%, 500 kg/m3 and 30%, and 500 kg/m3 and 40%) were better than those of the commercial 11-mm-thick gypsum board. Thus, it is concluded that rice hull–sawdust composite boards may be implemented as sound-absorbing barriers in construction due to their high sound absorption coefficients.