Maximum Sound Absorption Research Articles

Novel porous fiber-based composites with excellent sound-absorbing and flame-retardant properties

Novel ultralight porous fiber-based composites are a very attractive subject in the material chemistry and are enabled to promise applications in the sound absorption fields. In this work, it reported a facile strategy to prepare the flame-retardant, sound-absorbing, and mechanical enhancement porous fiber-based composites (PFC-EM-x) by using natural cellulose fiber, glass fiber, and flame retardant. Subsequently, the expandable microspheres (EMs) were added to construct the well-defined porous microstructure of materials for the enhancement in sound-absorbing performance. The results demonstrated that the high EMs contents had a remarkable influence on the porous structure of the composites so that the composites achieved the outstanding sound-absorbing performance and acceptable mechanical properties compared with other reported materials, especially as-prepared PFC-EM-20 composite showed excellent sound absorption at a range of high frequencies with the maximum sound absorption coefficient of 0.781 and tensile strength of 1.07 kN/m. Moreover, the limiting oxygen index values of all the samples were more than 26, both V1 and V2 rating in UL-94 test were achieved, which indicated that the obtained PFC-EM-x composites displayed outstanding flame retardancy. In summary, this study provides a facile strategy to rationally construct mechanically robust, highly efficient sound-absorbing and flame retardant ultralight composites which have promising applications in the future as green engineering materials.

Flame-Retardant and Sound-Absorption Properties of Composites Based on Kapok Fiber.

In order to improve the utilization rate of kapok fiber, flame-retardant and sound-absorption composites were prepared by the hot pressing method with kapok fiber as the reinforced material, polyε-caprolactone as the matrix material, and magnesium hydroxide as the flame retardant. Then, the effects of hot pressing temperature, hot pressing time, density of composites, mass fraction of kapok fiber, thickness of composites, and air layer thickness on the sound-absorption properties of composites were analyzed, with the average sound absorption coefficient as the index. Under the optimal process parameters, the maximum sound absorption coefficient reached 0.830, the average sound absorption coefficient was 0.520, and the sound-absorption band was wide. Thus, the composites belonged to high-efficiency sound-absorbing material. The flame-retardant effect of magnesium hydroxide on the composites was investigated, and the limiting oxygen index could reach 31.5%. Finally, multifunctional composites based on kapok fiber with flame retardant properties, and sound-absorption properties were obtained.

Maximum Sound Absorption by a Monopole in a Room at Low Frequencies

The article considers the problem of sound absorption by a monopole in a room with perfectly hard walls. The radiation impedance of a monopole in the form of a piston built into one of the walls was found. The impedance of the monopole is calculated that ensures the maximum damping constant of the room first natural resonance. It is shown that in the general case, a monopole with an impedance chosen in a certain way absorbs sound more efficiently than a Helmholtz resonator. The proposed approach can be used to design active sound absorption systems for small rooms.

Structural characteristics and sound absorption properties of poplar seed fibers

In order to make reasonable utilization of poplar seed fibers, their macromolecular structure, supramolecular structure and morphological structure were analyzed by means of a biological microscope, scanning electron microscope, Fourier transform infrared spectrometer and X-ray diffractometer, and the relationship between the structure of poplar seed fiber and its sound absorption performance was explored. The acoustic impedance transfer function method was used to test the sound absorption performance of poplar seed fiber, kapok fiber, cotton fiber, wool fiber and hemp fiber aggregates that could be used in the field of sound absorption. The results showed that the order of sound absorption properties of the five fiber aggregates was as follows: kapok fiber, poplar seed fiber, cotton fiber, wool fiber, hemp fiber. The special structure of poplar seed fiber meant it had excellent sound absorption performance in the entire tested frequency range. The poplar seed fiber aggregate had a wide sound absorption frequency band and the maximum sound absorption coefficient reached 0.84, which has high application value in the field of sound absorption.

Dynamic cushion, quasi-static stab resistance, and acoustic absorption analyses of flexible multifunctional inter-/intra-bonded sandwich-structured composites

This study proposes flexible multifunctional sandwich-structured composites that are reinforced by using aramid staple fibers and a needle-punching process and measures their cushion performance using a self-made drop-tower machine with a realistic depth sensor. The Mechanical properties of the laminated nonwoven composites are evaluated to examine the influence of the content of aramid staple fibers. Moreover, the puncture resistance rises linearly with the increasing aramid content. When the aramid content is 15%, the laminated nonwoven composites can bear 60.34% of dynamic impact force and have the maximum burst load of 1798.5 N, the maximum puncture resistance of 320.1 N, the maximum stab resistance of 191.9 N, the maximum sound absorption coefficient of 0.99, and NRC of 0.41. Therefore, aramid staple fibers are good candidate to be used as improvement in cushioning, stab resistant, and sound-absorbent properties of security walls.

Noise control material using jute (Corchorus olitorius): effect of bulk density and thickness

An attempt has been made to study the effect of thickness and compactness of natural fibre assembly in the reduction of noise. Fourteen available natural fibres i.e. banana, bhimal, roselle, coconut, cotton, wool, flax, hemp, jute, nettle, okra, pineapple, ramie, sisal and two synthetic sound absorbers i.e. rockwool, glass wool have been tested for sound absorption coefficient. Depending on availability and sound absorbency property, jute fibre (Corchorus olitorius), has been selected for detailed study. Test probe has been designed to test the fibre bundle in impedance tube principle. It is observed that there are significant absorption and transmission loss of sound energy through the jute fibre bundle either alone or covered with paper laminate. Statistical models based on second-order standard polynomial and Box and Benken factorial design, have been suggested to predict the sound transmission loss and absorption with respect to thickness and density in different frequency level of sound for stuffed fibre and paper panel stuffed with fibre. The correlation coefficients between observed and predicted values are above 0.95. Stuffed jute fibre shows maximum sound absorption with 30 mm thickness, 1.0 g/cm3 density in the application of 5000 Hz sound frequency. In case of transmission loss for below 18 mm thickness, jute fibre stuffed paper laminate panel shows increase up to 1.0 g/cm2 and then decrease. The sound loss reaches the maximum in the application of 1500 Hz frequency and then remains constant. Therefore, it can be effectively used as sound absorber or barrier protecting the environment from sound pollution, if designed properly. The knowledge from this study can help to design sound insulator or barrier from an industrial crop like jute.

Sound and Vibration Damping Properties of Water Retted Kenaf Bast Fiber (WKF) and Poly (Butylene Succinate) PBS

Nowadays, considerable attention has been paid on the utilization of natural materials to reduce the carbon emission from material synthesis. In this study, the sound and vibration damping properties of natural material based Poly Butylene Succinate(PBS) and Water Retted Kenaf Bast Fiber(WKF) were explored and characterized. The goal is to characterize the sound absorption and damping properties of the PBS and WKF at difference materials percentage. The (material)PBS and WKF are produced by using Compression moulding machine model Gotech GT-7014-H and the sample thickness is 3 mm. The vibration damping measurement of the material is carried out based on the free vibration method technique. It is observed that the damping factor is obtained is 0.0469 for PBS material. The measurement of the sound absorption coefficient of the PBS and WKF is carried out using the impedance tube. The result shows that the maximum sound absorption of 0.305 was observed at a frequency of 642 Hz for PBS material. Whereas Tensile Strength, for PBS material shows 26.33 MPa. These results suggest that the PBS could be a viable candidate for applications which need good sound and vibration properties.

Soundproofing performance of flexible polyurethane foams as a fractal object

Noise pollution is one of the most severe environmental concerns due to its damaging effects on human health. This study aimed to evaluate the relationship between the acoustic damping behavior and fractal dimension (Df) of flexible polyurethane foams (FPUFs) manufactured by different synthesized linear saturated aliphatic polyesters (LSAP) resins, methylene diphenyl diisocyanate (MDI), etc. (isocyanate index = 110 & water content = 5%). Cellular and soundproofing properties of FPUFs were evaluated by an optical microscope and impedance tube device. Df was calculated by the box-counting method after binarization and image processing of FPUF images. Results indicate that by increasing Df from 1.5415 to 1.8554, the total sound absorption performance (S) of FPUFs improves by 43.07% and the maximum sound absorption coefficient reaches 0.98. The relation between S and Df was obtained as follows: Log(S) = 0.4583 Df + 2.6659, r2 = 0.9298. Generally, decreasing the cell size and increasing the cell size distribution and open-cell content, increase Df and irregularity of FPUFs. The results reveal that FPUFs with an optimum condition of cell size of 180–200 μm, open-cell content of 30%, and density of 110 (Kg.m−3) have the highest Df and can be a promising candidate as sound insulating materials.

A Novel Acoustic Sandwich Panel Based on Sheep Wool

The aim of this paper is to propose a novel sandwich panel, which would be suitable for sound absorption and airborne sound insulation, used as applied cladding or independent lightweight partition wall. As far as the authors are concerned, this is the first sheep wool-based sandwich panel using only natural materials. The structure was prepared using hydrated lime-based composite face sheets and a sheep wool-based core. Several parameters of the sandwich panel were determined, including sound absorption coefficient, airborne sound insulation, thermal conductivity, thermal resistance, compressive strength, and bending strength, respectively. The results indicate that the maximum sound absorption value of 0.903 was obtained at the frequency of 524 Hz in the case of the unperforated sample, 0.822 at 536 Hz in the case of the sample with 10% perforations, 0.780 at 3036 Hz in the case of the sample with 20% perforations, and 0.853 at 3200 Hz in the case of the sample with 30% perforations. The registered airborne sound insulation index of the panel was 38 dB. Based on the obtained data, it can be concluded that the studied panel recorded comparable values with other synthetic noise control solutions, which are suitable as applied cladding or an independent lightweight partition wall, with good acoustic properties.

Optimization of micro-perforated sound absorber using Particle Swarm Optimization (PSO)

This study investigates the acoustic properties of micro-perforated panel (MPP) as an alternative to passive noise control. In order to obtain high sound absorption over broad frequency band, the analysis of sound absorption performance of MPP sound absorber should be conducted based on 3 major design parameters, such as perforation diameter, d, air cavity depth, D, and distance between perforations, b, of MPP. Next, the optimization of sound absorption coefficient for MPP sound absorber need to be done by using the Particle Swarm Optimization (PSO) algorithm and the optimum parameters of a single layer MPP sound absorber should be obtained for achieving higher sound absorption which the sound absorption coefficient, α + 0.5 with a wider frequency band. The PSO is used in order to optimize the panel construction to provide maximum sound absorption coefficient in a determined wide band frequency range. Experiments are carried out at normal sound incidence and plane waves. A good agreement is achieved between the theory and the experiments.

A novel sound absorbing material comprising discarded luffa scraps and polyester fibers

Abstract For promoting the recycling of industrially discarded luffa resources and preventing environmental pollution caused by the incineration of luffa waste, abundant luffa scraps and environmentally friendly polyester fibers were used as raw materials to produce luffa fiber sound absorbing composites by the clean hot-pressing technology. Results revealed that the polyester fiber surface becomes rougher, with a large number of porous structures, affording a three-dimensional network after hot-pressing. Within the range of the test design, the sound absorption coefficient of the samples increased with increasing density, thickness, and distance of the back air gap. With the increase in the thickness from 2 cm to 6 cm, the average sound absorption coefficient of the material increased from 0.442 to 0.684, and the maximum sound absorption coefficient increased from 0.907 (4000 Hz) to 0.991 (1000 Hz). At back air gap distances of 0 cm, 1 cm, and 2 cm, their average sound absorption coefficients were 0.602, 0.606, and 0.645, respectively. At a density of 0.09 g/cm3, a thickness of 4 cm, and a back air gap distance of 2 cm, the average sound absorption coefficient of the luffa fiber composite reached 0.645, revealing a high-efficiency sound absorbing material. In addition to exhibiting a good sound absorption performance, the luffa fiber composite exhibited a soft surface and good buffer performance. Moreover, compared to other plant fiber composites, the luffa fiber composite exhibited better performance for hygroscopic and moisture dissipation.

Groundnut shell / rice husk agro-waste reinforced polypropylene hybrid biocomposites

Lignocellulosic agricultural residues are unavoidably generated and are mostly disposed by burning or burying which causes significant pollution. Using these materials for value added applications can contribute to a greener environment. In this work, two such agricultural residues namely, rice husk (RH) and groundnut shell (GNS) were used without any treatment to prepare hybrid polypropylene (PP) biocomposites for green building materials. The effects of % reinforcement on the thermal insulation, sound absorption, aqueous stability, flame resistance along with mechanical properties were tested. The unique wedge shaped morphology of rice husk and its low aspect ratio played a significant role in influencing the properties of the composites. The composites possessed good tensile and flexural strength (highest value of 15.6 MPa and 37.6 MPa respectively at the 20/60/20 GNS/RH/PP ratio). Thermal conductivity of the composites varied from 0.156 to 0.270 W/mK. The maximum sound absorption coefficient was 0.48. Flame retardancy of the composites were on par with the commercially available gypsum based ceiling tiles. Water absorption of the composites was about 85% lower than that of the gypsum tiles addressing a major drawback of gypsum based ceiling tiles. The properties of the composites were comparable to several other biocomposites reported as well.

Mathematical model of sound absorption by lungs with acoustic stimulation of the respiratory system

According to the results of theoretical and experimental analysis of the characteristics of the propagation of acoustic oscillations in the respiratory system, it is necessary to determine the resonant frequency of the respiratory tract to increase the vital capacity of the lungs by opening back-up alveoli by acoustic stimulation of the respiratory system, and then to affect the respiratory system maximum sound absorption range (at a level of ±3 dB from the maximum value of the absorption coefficient).

Mathematical Model of Sound Absorption by Lungs with Acoustic Stimulation of the Respiratory System.

According to the results of theoretical and experimental analysis of the characteristics of the propagation of acoustic vibrations in the respiratory system, it is necessary to determine the resonant frequency of the respiratory tract to increase the vital capacity of the lungs by opening reserve alveoli by acoustic stimulation of the respiratory system and then to affect the respiratory system with scanning tonal sounds in the maximum sound absorption range (at a level of ±3 dB of the maximum absorption coefficient value).

The effect of the combination of multiple woven fabric and nonwoven on acoustic absorption

Textile materials can be used as acoustic materials. In this study, the acoustic absorption coefficient of multilayer fabrics with 60 ends/cm and 15, 30, 45, and 60 picks/cm is measured when the fabric is added as a resistive layer on top of a polyester nonwoven, in order to study the influence of the fabric spatial structure in the acoustic absorption of the assembly. Five different fabric structures are used. Design of experiments and data analysis tools are used to describe the influence of two manufacturing factors on the sound absorption coefficient of the ensemble. These factors are the fabric weft count (picks/cm) and the thickness of the nonwoven (mm). The experimental conditions under which the maximum sound absorption coefficient is achieved are found. The influence of each factor and a mathematical model are obtained. Results of statistical and optimization analysis show that for the same fabric density, sound absorption coefficient increases as the number of layers decreases.

Study of Acoustic Properties of Chicken Feather Fibre (CFF) and Its Hybrid Composites

ABSTRACT This study discusses the effect of molding temperature, molding pressure and molding time on the final compression molded CFF and its hybrid composites for its acoustic property. The results of tests like sound absorption coefficient, noise absorption coefficient (NRC) value, thickness and density of composites conducted to characterize the bio-composites developed with different fiber loads of chosen fiber and processing conditions, are discussed in this study. When comparing the overall results on the acoustic property of the composites, 100% CFF composite showed highest NRC of 0.6 by keeping the process variables at lower conditions (165°C temperature, 5 Bar pressure and 3-min time). The influence of temperature and pressure is significant on the NRC value than time on the acoustic properties of the composite board. If the fiber loading of CFF rise, the NRC value also increased. The maximum sound absorption observed at 1.8 KHz because of the natural frequency of the CFF material. The processing conditions, reinforcement fiber wt%, thickness and density have a significant impact on the NRC values.

Preparation and property evaluations of zeolite rigid foam composites

AbstractPolyether polyol, isocyanate, and a flame retardant (10 wt%), zeolite (0 wt%, 1 wt%, 3 wt%, 5 wt%, 7 wt%, and 9 wt%) are used to form the rigid polyurethane (PU) foam, while a nylon nonwoven fabrics (400 g/m2) and a polyester aluminum foil are combined to serve as the panel. The rigid PU foam and the panel are combined to form the rigid foam composites. The cell structure, compressive stress, combustion resistance, thermal stability, thermal conductivity, sound absorption, and electromagnetic shielding effectiveness (EMSE) of the rigid foam composites are evaluated, examining the effects of using flame retardant agent and zeolite. When the zeolite is 5 wt%, the rigid foam composites have an optimal density of 0.172 g/cm3, an average cell size of 0.2131 mm, a maximum compressive stress of 460.03Kpa, an optimal LOI of 28, and optimal EMSE of 40 dB, and the maximum thermal stability, thermal insulation, and sound absorption.

Sound Absorption Properties of DFs/EVA Composites.

Using discarded feather fibers (DFs) and ethylene vinyl acetate (EVA) copolymer, the DFs/EVA composites with good sound absorption performance were prepared by hot-pressing method. The effects of hot-pressing temperature, mass fraction of DFs, density and thickness of composites on the sound absorption properties were studied by the controlling variable method. The sound absorption properties of the composites were studied by the transfer function method, and under the optimized technological conditions, the sound absorption coefficient of the composites was above 0.9 and the sound absorption band was wide. According to the box counting method based on the fractal theory, the fractal dimension of DFs/EVA sound absorption composites was calculated through Matlab programming, and the relationship between the fractal dimension and the mass fraction of DFs, the volume density of the composites were analyzed, then the quantitative relationship between the fractal dimension and the maximum sound absorption coefficient was deduced, which played a major role in the sound absorption design of porous sound absorption materials.

Design of acoustic foam wedge panels by finite element frequency domain acoustical analysis

Acoustic foam wedge panels provide good sound absorption qualities in the mid and high frequency ranges. In this study, a finite element frequency domain acoustical analysis is used for analysis. Such a numerical method is more efficient than the earlier studies by saving the calculation time on the elements of the incident acoustic field. During the design of a wedge panel, the cross-sectional width and the area of one section of the wedge panel are kept the same throughout the study. By varying the wedge angle, the maximum sound absorption capability of the wedge foam can be found. It is concluded that in the interested frequency regions, 100–4000 and 2000–4000 Hz, the wedge foam with wedge angle of 31° has the excellent sound absorption capability.

Extrusion Foaming of Lightweight Polystyrene Composite Foams with Controllable Cellular Structure for Sound Absorption Application.

Polymer foams are promising for sound absorption applications. In order to process an industrial product, a series of polystyrene (PS) composite foams were prepared by continuous extrusion foaming assisted by supercritical CO2. Because the cell size and cell density were the key to determine the sound absorption coefficient at normal incidence, the bio-resource lignin was employed for the first time to control the cellular structure on basis of hetero-nucleation effect. The sound absorption range of the PS/lignin composite foams was corresponding to the cellular structure and lignin content. As a result, the maximum sound absorption coefficient at normal incidence was higher than 0.90. For a comparison, multiwall carbon nanotube (MWCNT) and micro graphite (mGr) particles were also used as the nucleation agent during the foaming process, respectively, which were more effective on the hetero-nucleation effect. The mechanical property and thermal stability of various foams were measured as well. Lignin showed a fire retardant effect in PS composite foam.