High Sound Absorption Research Articles

The sound absorption of sisal fiber and sisal fiber/polyethylene film sheets: Morphology and structure

Sisal fiber (SF) and waterborne polyurethane adhesive were used to prepare SF‐based sound absorption material through hot press molding. SF with elastic polyethylene (PE) film interlayers was also fabricated as a new type of sound absorbing composite. The effects of SF treatment methods and PE film on sound absorption coefficient were evaluated. The alkaline‐treated SF composite had higher sound absorption as compared with the untreated SF composite when the sound wave was below 5500 Hz. The sound absorption peak of alkaline/oxidation‐treated SF composite moved towards low‐ and middle‐frequency regions. The SF/PE film composite showed that at low‐frequency the more layers of PE film inserted the better sound absorption property. The mass‐temperature relationship and FTIR of the composites were discussed. The SF surface and the cross section of the composites were observed by SEM, which showed the void structure and microfiber contributed to enhancing sound absorbing property. POLYM. COMPOS., 39:2812–2818, 2018. © 2016 Society of Plastics Engineers

Implementation of the Additive PolyJet Technology to the Development and Fabricating the Samples of the Acoustic Metamaterials

This paper describes the development of the additive PolyJet technology aimed at designing and fabricating the samples of acoustic metamaterials with high sound absorption. The samples in the form of cellular thin-walled periodic structures with links between the cells are synthesized by photopolymer material using the additive technology. The peculiarities of the synthesized process are studied and optimal parameters are found to provide the required shape of the samples. The results of experimental study of sound absorption efficiency of the synthesized samples are also presented that demonstrate rather high sound absorption efficiency.

Study on sound absorbing mechanism of MPP affected by bending resonance of panel

Followed by the study (Sakagami et al., 2010a) about the micro-perforated panel (MPP) with honeycomb structure, in this paper, the MPP for vehicle noise, vibration and harshness (NVH) performance development is studied, where the MPP prototype is moulded by a sophisticated 3D printer, and its sound absorption coefficients are measured by the experiment of acoustic impedance tube. Two proposals are made according to the interpretation of absorbing mechanism. One is the potentiality of thin MPP not combined but contacted with honeycomb core, which might cause higher sound absorption by the induced sound impact effect. The other is the potentiality of 3D-MPP that increases the design parameters by the mass and the depth of aperture as well as the diameter and the pitch among apertures.

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.

Laboratory Evaluation of Sound Absorption Characteristics of Pervious Concrete Pavement Materials

This paper describes a laboratory study on the sound absorption characteristics of clogged and unclogged pervious concrete (PC) pavement materials compared with those of porous asphalt (PA) mixtures and those of conventional dense-graded asphalt and portland cement concrete pavement materials. Examined in this study were the effects of the mixtures’ initial porosity on their sound absorption characteristics and how these characteristics were affected by subsequent clogging of the mixtures. Four porosity levels of PC and PA were studied: 10%, 15%, 20%, and 25%. The mixtures with 20% porosity were tested for the effects of clogging. The test results showed that the shapes of sound absorption spectra of PC and PA materials were similar displayed high sound absorption values within the frequency range of 250 to 1,000 Hz. However, for all four porosity levels studied, the PC materials produced about 0.1 or 20% higher sound absorption coefficient values throughout the entire measured frequency range from 100 to 2,500 Hz. The same order of magnitude of differences in the sound absorption values between PC and PA was also observed in their clogged states. The finding that PC exhibits a better sound absorption capability than PA is of practical significance. The results of this study also demonstrate that laboratory testing of sound absorption can be employed to provide a useful indicative assessment of the noise reduction properties of porous pavement materials without the need for full-scale field testing.

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.

Hygrothermal performance of hempcrete for Ontario (Canada) buildings

Hempcrete is a bio-aggregate based composite material used for building envelopes which typically consists of hemp shiv (hurd), lime binder and water. Hempcrete has several distinct advantages including low thermal conductivity, effective moisture buffering, and high sound absorption, while having a high carbon sequestration “index”. This work investigates the impact of mix proportions on hempcrete properties and the hygrothermal performance of two proposed hempcrete wall assemblies for Ontario, Canada. The experimental results highlight the significant influence of the binder on the density and thermal conductivity of the final material. Thermal conductivity measurements ranged from 0.074 to 0.103 W/mK. Finally, hygrothermal analysis demonstrated that when using hempcrete in the Canadian climate a rain screen wall system is more suitable than a mass wall.

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.

Fabrication of polyurethane composite foams with magnesium hydroxide filler for improved sound absorption

In automobile industry, sound absorption material has huge importance because of noise, vibration, harshness (NVH) control. Polyurethane foam is commonly used as a sound absorption material because of its high sound absorption efficiency. In this study, magnesium hydroxide filler is used in fabricating polyurethane composite foams for improving acoustic property. Use of the filler improves the sound absorption efficiency not only with enhancing damping motion by the fillers but also with increasing the number of partially opened pores. Noise reduction coefficient was improved about 70% at the optimum open porosity of 0.63 compared with the non-filler case. Fine cell morphology with well-developed cavity and pore structures is advantageous in obtaining high sound absorption efficiency. The optimum open porosity is achieved at the filler content of 1.0wt% for the highest noise reduction coefficient.

Influence of sorption on sound propagation in granular activated carbon.

Granular activated carbon (GAC) has numerous applications due to its ability to adsorb and desorb gas molecules. Recently, it has been shown to exhibit unusually high low frequency sound absorption. This behavior is determined by both the multi-scale nature of the material, i.e., the existence of three scales of heterogeneities, and physical processes specific to micro- and nanometer-size pores, i.e., rarefaction and sorption effects. To account for these processes a model for sound propagation in GAC is developed in this work. A methodology for characterizing GAC which includes optical granulometry, flow resistivity measurements, and the derivation of the inner-particle model parameters from acoustical and non-acoustical measurements is also presented. The model agrees with measurements of normal incidence surface impedance and sound absorption coefficient on three different GAC samples.

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.

Acoustical and mechanical properties of thermoplastic composites from discarded carpets

Abstract Without additional matrix or reinforcement, compression molded composites from waste polypropylene (PP) carpets/nylon (PA) carpets or PP carpets/polyester (PET) carpets have higher mechanical properties and sound absorption than traditional jute/PP composites. Large amount of carpets have been discarded every year, leading to waste of petro-based materials and serious environmental pollution. Fabrication of composites from discarded carpets via compression molding could save petroleum resources and alleviate environmental pressure. In this research, the compression molded composites from waste PP/PA carpets or PP/PET carpets showed good mechanical properties, sound absorption and water stability. Compared to the jute/PP composites, nylon 6,6 (PA66)/PP carpet composites had 37% and 9% higher flexural strength and impact resistance, as well as 45% and 10% higher sound absorption and water stability, indicating their potential for transportation and construction industries.

Study of vibro-acoustic properties of composite materials based on polyurethane injection

AnnotationModern standards of noise and vibration make the manufacturers of vehicles, machines and construction materials take into account the high demands in the design process. Often there is a need both in vibrations absorbing and in effective sound absorbers. Therefore there was a research on the concentrations of matrix components, fillers and modifiers impact on the absorbing and elastic properties of the polyurethane composites. The evaluation of sound-absorbing and elastic properties was in determination of sound absorption coefficient Cs and dynamic elasticity modulus Ed of developed composite materials. The aim of this work is to study changes in the properties of composite materials based on polyurethane matrix to identify compounds with the highest sound absorption and vibration absorbing properties simultaneously.

COMPARISON ON ACOUSTIC PERFORMANCE BETWEEN DUST AND COIR FORM EMPTY FRUIT BUNCHES (EFB) AS SOUND ABSORPTION MATERIAL

Positive growth in palm oil Industry resulting in large quantities of solid waste generation and created a major disposal problem to the country. Among the major solid wastes generated from oil palm manufacturing processed are empty fruit bunches (EFB), mesocarp fruit fibres (MF) and palm kernel shells (PKS). This study investigated the utilization of EFB as sound absorption material for noise control in building. The effect of different form of EFB (coir and dust) was investigated in three different thicknesses (6mm, 12mm and 18mm) to determine the maximum sound absorption coefficient (SAC) and optimum frequencies. All samples were tested using impedance tube at low and high frequencies guided by BS EN ISO 10534. Results shows that dust EFB samples absorbed more sound energy compared to coir EFB samples at both low and high frequency region. Maximum SAC obtained by 18mm thick dust EFB samples at low frequency is 0.6 at 1500Hz while at high frequency; the maximum absorption was also obtained by 18mm thick dust EFB samples with SAC value of 0.990 at 3750Hz. This result indicated that thicker samples absorbed more sound energy compared to thinner samples. Moreover, small particles fibers consequently create less pores to the samples with higher density and higher sound absorption. In conclusion, palm oil fibre is highly potential to be used as raw material for sound absorption material replacing synthetic materials since these fiber are renewable, cheaper, nonabrasive, abundance and give less negative effect to human health.

Speed-of-sound measurements in (argon + carbon dioxide) over the temperature range from (275 to 500) K at pressures up to 8 MPa

The speed of sound of two (argon+carbon dioxide) mixtures was measured over the temperature range from (275 to 500)K with pressures up to 8MPa utilizing a spherical acoustic resonator. The compositions of the gravimetrically prepared mixtures were (0.50104 and 0.74981) mole fraction carbon dioxide. The vibrational relaxation of pure carbon dioxide led to high sound absorption, which significantly impeded the sound-speed measurements on carbon dioxide and its mixtures; pre-condensation may have also affected the results for some measurements near the dew line. Thus, in contrast to the standard operating procedure for speed-of-sound measurements with a spherical resonator, non-radial resonances at lower frequencies were taken into account. Still, the data show a comparatively large scatter, and the usual repeatability of this general type of instrument could not be realized with the present measurements. Nonetheless, the average relative combined expanded uncertainty (k=2) in speed of sound ranged from (0.042 to 0.056)% for both mixtures, with individual state-point uncertainties increasing to 0.1%. These uncertainties are adequate for our intended purpose of evaluating thermodynamic models. The results are compared to a Helmholtz energy equation of state for carbon capture and storage applications; relative deviations of (−0.64 to 0.08)% for the (0.49896 argon+0.50104 carbon dioxide) mixture, and of (−1.52 to 0.77)% for the (0.25019 argon+0.74981 carbon dioxide) mixture were observed.

Compression‐molded composites from waste polypropylene carpets

In this research, compression‐molded composites were developed from discarded polypropylene (PP) carpets and showed good mechanical properties, water stability and acoustic property. Compared to jute/PP composites, the composites from PP carpets had 14%, 20%, and 40% higher flexural strength, impact resistance, and elastic modulus, respectively. In addition, with 58.3% and 14.5% higher sound absorption and water stability than jute/PP composites, the composites from carpets demonstrated good potential for industrial applications and could promote sustainability of material industries. POLYM. COMPOS., 39:595–605, 2018. © 2016 Society of Plastics Engineers

Compression molded composites from discarded nylon 6/nylon 6,6 carpets for sustainable industries

Discarded carpets with high amount of petroleum-based fibers are usually disposed in landfills, leading to waste of high value petro-polymers and environmental pollution. A novel method to reuse nylon carpet targeting environmental protection and material saving was developed. Recent studies showed that melt blended nylon carpet composites by screw extruder had low mechanical properties and disqualified carpet composites in transportation and construction industries. In this research, compression molded composites from discarded nylon 6/nylon 6,6 carpets had good sound absorption, mechanical properties and water stability. As compared with jute/PP composites, the compression molded composites from nylon 6/nylon 6,6 carpets had up to 40%, 59%, 124% and 32%, higher sound absorption, flexural strength, elastic modulus and impact resistance, respectively. Unshredded nylon 6,6 carpet yarns and styrene-butadiene-rubber/calcium-carbonate binders in carpets reinforced nylon 6 and polypropylene, and thus made the composites strong. Styrene-butadiene-rubber particles and multiple interfaces in the multi-component composites endowed compression molded nylon 6/nylon 6,6 carpet composites with good sound absorption. Developing compression molded carpet composites with good mechanical properties and sound absorption provides a new method of reusing carpets.

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.

Sound absorbent, flame retardant warp knitting spacer fabrics: Manufacturing techniques and characterization evaluations

This study proposes a combination for reciprocal reinforcement between warp knitting spacer fabrics and PU foams. PET/Kevlar nonwoven fabrics are made with an 80:20 ratio and an incorporation of various needle-punching speed of 100, 150, 200, 250, and 300 needles/min. Ascribing to having an optimal bursting strength, sound absorption coefficient, and limited oxygen index (LOI), the PET/Kevlar nonwoven fabric that is made by 200 needles/min are selected to be combined with a glass-fiber fabric by applying needle punch in order to form a surface layer. Next, warp knitting spacer fabrics and the nonwoven fabrics are laminated, followed by being combined with polyurethane (PU) foam that are featured with different densities of 200, 210, 220, 230, and 240 kg/m3 in order to form spacer fabric/PU foam composites with multiple functions. The composites are then tested with a drop-weight test, a compression test, a bursting strength test, a sound absorption test, and a horizontal burning test. The test results indicate that all spacer fabric/PU foam composites reach a horizontal burning level of HF1, and their sound absorption coefficients at 2500-4000 Hz also suggest a satisfactory sound absorption. In particular, the optimal residual stress and compressive strength are present when the composites contain 210 kg/m3 PU foam. Similarly, the optimal bursting strength of the composites occurs when they are composed of 230 kg/m3 PU foam. The spacer fabric/PU foam composites are proven to have high strengths, sound absorption, and fire retardant, and thus have promising potentials for use as construction materials and light weight composite planks.