Sound Absorption Coefficient Values Research Articles

Effect of air gap on sound absorption in layered composite structures produced of sustainable materials

Numerous materials have been produced to isolate the noise that negatively impacts people’s health and productivity at work. Some of these materials are not preferred for usage because they are expensive, inefficient, or harmful to the environment. In this study, composite materials were produced with waste chicken feathers (CF) and polyvinyl acetate (PVAC) binder in different mixture ratios. After CF was washed and cleaned, it was shredded into 2–3 mm lengths with a chopper. Then CF was mixed with PVAC binder and thermal bonding was applied. As a result of the process, composites with a thickness of 10 mm and dimensions of 15 cm × 15 cm were formed. These composite plates are supported by sandwich constructions made of various varieties of polyester-based felt (NW), knitted fabric (KF), leather (L), spacer fabric (SF), and air gap (AG5, AG10, AG15) in thicknesses of 5, 10, and 15 mm. Impedance tubes with four microphones were used to evaluate the sound absorption coefficient and sound transmission loss values of these manufactured structures, and the resulting data were analyzed. According to this; The NW + CFC1 two-layer structure is 0.33 (500 Hz), but when a 15 mm thick air gap layer is added, it is seen that it increases to 0.85 (500 Hz). Other sandwich structures produced also show similar results. The best results were achieved with layered composite structures. Adding an air gap layer between the composite layers to increase sound absorption has improved results, especially at low frequencies. The air gap layer can significantly reduce production costs because it can be used instead of a material layer. The production of textile-based sound insulation structures from the waste material CF is also of great importance in terms of sustainability.

SOUND AND THERMAL INSULATION PROPERTIES OF SANDWICH COMPOSITES MADE OF WASTE KEVLAR® MATERIALS

This paper examines the thermal and acoustic insulation characteristics of sandwich composites with waste Kevlar® fiber-reinforced face materials and polyurethane/paper cardboard cores. Waste Kevlar® short fibers (carding waste) were reinforced into the sandwich composites’ core part in varying ratios (2%, 5%, and 10%). Kevlar® fabric edge waste (waste of weaving process) was used to produce the face materials of sandwich composites. Sandwich composites were also stitched using Kevlar® yarns to observe the effect of the through-thickness reinforcement on sound and thermal insulation properties. The sound insulation test results showed that reinforcement of short Kevlar® fibers into the core parts of sandwich composites somewhat raised their sound absorption coefficients. Because the stitching holes created air spaces for sound vibrations, the sound absorption coefficient values improved. The sound transmission losses of sandwich composites were also increased up to 30 dB after short Kevlar® fiber addition. The thermal conductivity coefficient of sandwich composites decreased, indicating that the addition of Kevlar® fibers increased their insulation properties.

Freeze-cast porous Al2O3/MgO ceramics as potential acoustic sound absorption

In acoustic engineering and architecture, materials called acoustic absorbers are widely used. There are currently numerous options for such materials, and many more are being researched. This study is conducted on porous ceramics produced via the freeze-casting process to propose new solutions with unique properties, like resistance to harsh environments. The freeze-casting method allows for the controlled creation of open-connected porous structures for different class materials through the cryogenic freezing of the suspension. The material samples are produced with Al2O3 (alumina)/MgO (magnesium oxide) material using camphene as solvent. The specimen samples are prepared using three different concentrations of the two solid components (60/40, 72/28, and 90/10 in weight). Each sample concentration achieves different morphology phase compositions and porous structures. Hence, we explore in the paper how those concentration parameters could interfere with acoustic absorption. Further, the samples were characterised using numerical and experimental methods related to sound absorption and microstructure. The 60/40 and 90/10 samples achieve sound absorption coefficient values upwards of 0.7 around the 2000-3000 Hz frequency range. The microstructure characteristics show the porosity gradually changing along its thickness, interfering with their sound absorption properties. Our findings highlight the complexities of characterising porous ceramics and emphasise the significance of understanding some material composition factors affecting sound absorption. Hence, this study provides valuable insights into the intricate nature of porous ceramic freeze-cast materials and their acoustic properties, substantially contributing to the ongoing exploration in this domain.

Investigation into the Acoustic Properties of Polylactic Acid Sound-Absorbing Panels Manufactured by 3D Printing Technology: The Influence of Nozzle Diameters and Internal Configurations.

Sound-absorbing panels are widely used in the acoustic design of aircraft parts, buildings and vehicles as well as in sound insulation and absorption in areas with heavy traffic. This paper studied the acoustic properties of sound-absorbing panels manufactured with three nozzle diameters (0.4 mm, 0.6 mm and 0.8 mm) by 3D printing from three types of polylactic acid filaments (Grey Tough PLA; Black PLA Pro; Natural PLA) and with six internal configurations with labyrinthine zigzag channels (Z1 and Z2). The absorption coefficient of the sample with the Z2 pattern, a 5.33 mm height, a 0.6 mm nozzle diameter and with Black PLA Pro showed the maximum value (α = 0.93) for the nozzle diameter of 0.6 mm. Next in position were the three samples with the Z1 pattern (4 mm height) made from all three materials used and printed with a nozzle diameter of 0.4 mm with a sound absorption coefficient value (α = 0.91) at 500 Hz. The highest value of the sound transmission loss (56 dB) was found for the sample printed with a nozzle size of 0.8 mm with the Z2 pattern (8 mm height) and with Black PLA Pro. The extruded material, the nozzle diameter and the internal configuration had a significant impact on the acoustic performance of the 3D-printed samples.

Characterization of an Arundo donax-based composite: A solution to improve indoor comfort

Arundo donax (giant reed or giant cane) is a widely available, perennial, invasive, non-food crop, present worldwide and employed for several uses, including building practices. Considering the increasing demand for sustainable building materials, A. donax can be an efficient solution. This study investigated its properties as a bio-aggregate mixed with a sodium silicate solution as an adhesive. A horizontal analysis that provided a general characterization of the composite was carried out. The results showed that the A. donax-based composite had an apparent density of 517 kg/m³, thermal conductivity of 0.128 W/(m.K), and high hygroscopicity, with a moisture buffering value of 4.33 g/(m² %RH), property that could be both an advantage for indoor comfort and a drawback. The uncommon sound absorption behaviour can be comparable to granular materials, with the highest sound absorption coefficient values, α, between 600 Hz and 700 Hz. Due to the range and the shape of the acoustic absorption property, this material may be helpful in acoustic treatments for speech noise. The mechanical tests defined flexural and compressive strength, respectively, 0.35 N/mm² and 0.9 N/mm², ensuring applicability. Above all, these tests opened new possible solutions for A. donax-based composite production either alone or in combination with other agro-industrial wastes and justified further tests, such as fire resistance and bio-susceptibility.

Pengaruh Komposisi Partikel Styrofoam dan Resin Epoksi pada Komposit Peredam Suara

<p><em>Styrofoam</em><em> (Extruded Polystyrene) waste can be used as a soundproofing material. This study aims to determine the effect of the particle composition of Styrofoam and epoxy resin on the performance of soundproofing composites. The composition between Styrofoam particles and epoxy resin is 20:20; 20:30; and 20:50 grams. Sound absorption test using PVC impedance tube 100 cm long, 15 cm diameter, and 5 mm thick. The variation in the placement distance of the composite from the sound source is 25; 50; and 75 cm and was measured using the sound level meter application. This type of test sound uses a single tone in the frequency range of 0-600 Hz which is recorded per 5 seconds. Composite performance analysis is reviewed based on media density, composite morphological characteristics of Image-J software, and sound absorption coefficient values. The results showed that the greater the composition had increased the density value of composite particles accompanied by a decrease in pore area in the composite media which resulted in a sound absorption coefficient of 15.61 dB at a composition of 20:50 with a distance of 25 cm from the sound source.</em></p>

Determining mechanical and acoustical behaviors of all-recycled PP sandwich structures with bi-directional sinusoidal corrugated core

By recycling the waste polymer material and using it in weight reduction studies of electric vehicles, a double-sided gain is achieved against environmental pollution. Sandwich structures with prismatic cores obtained by recycling waste polymers can be used in structural applications of light and heavy commercial vehicles and public transportation vehicles that carry cargo and passengers. These sandwich vehicle parts could help to increase the max. range and load-carrying capacity of electric vehicles. In this study, sandwich plates with prismatic egg-box cores were produced with waste Polypropylene. Since the materials are collected from different waste sources, the physical properties (additive ratio, secondary substance determination, density) of the recycled material were measured. Thereafter, hardness, quasi-static flatwise and edgewise compression, and 3-point bending tests were done to determine the mechanical properties of the structure. After that, dynamic compression and 3-point bending tests were performed to determine the strength and impact energy absorption capacity of the structure in collision situations. Finally, impedance tube tests were carried out for the acoustic characterization, which is one of the important parameters affecting interior cabin comfort, and Sound Transmission Loss (STL) and Sound Absorption Coefficient (SAC) values of the structure were determined.

Thermal performance and sound absorption capability of water hyacinth stems-based materials

The main aim of this study was to assess the efficacy of water hyacinth stem as insulation material by analysing its thermal and acoustic performance. Several particleboards and composites were prepared by adding either binders or blending water hyacinth stem with other construction materials. During the preparation of the samples, various factors including sample thickness, average particle size of water hyacinth stem in the samples, degree of compaction, and type of binder used were taken into consideration. Particleboards manually compacted prepared with water hyacinth stem particles size range of 1–2 mm and a 14 mm thickness showed the lowest thermal conductivity coefficient and highest value of the weighted absorption coefficient. Additionally, composites prepared with water hyacinth stem particles mixed with gypsum reached lower thermal conductivity and higher sound absorption coefficient values than those observed for cement-based composites obtained under the same preparation conditions. The values found in this study and those published in the literature for other types of biomass materials suggest that water hyacinth stem has significant potential for use, either alone or in combination with other materials, as a thermal and acoustic conditioning material.

Study on Sound Absorption of Road Acoustic Screens Under Simulated Weathering

The present paper is comparing the results of research studies carried out for three road acoustic screens of different design and different number of damping layers. For the tests, we selected timber or steel screens with a traditional multilayer structure and also one innovative type of simplified design. With respect to particular panels, their sound absorption properties were investigated in the reverberation chamber after they had been subjected to simulated weathering. In the process, two screens were subjected to the aging tests of 50–500 cycles in a special climatic chamber, and the innovative screens were subjected to 1000 cycles. The procedure was repeated every 50 or 100 cycles in order to obtain the changes of acoustic characteristics. The changes taking place in the absorbing material were also investigated with the use of scanning electron microscopy method (SEM). Basing on the obtained results and on the statistical analysis, the capability to maintain acoustic properties by the panels during their service life in natural conditions was estimated. For that purpose, linear statistical models were worked out, which were then applied to estimate the value of the single number sound absorption coefficient after successive aging cycles as well as the predicted time periods of acoustic class changes.

Sound Wave Absorption Coefficient and Sound Velocity in Thermally Modified Wood

The present work analyses the absorption coefficient of sound waves and the speed of sound propagation in thermally modified wood. The high resistance to weathering, fungi, and better dimensional stability, and therefore the broad physical properties of this material, are well known. However, the literature lacks numerous analyses of its acoustic characteristics. During the study, high-density species, such as oak, red oak, and beech were used, in contrast to pine. Pine wood during this test was characterised by a most rapid increase in the sound absorption coefficient value, in the range of 1000–6300 Hz, and reached the highest value from all wood species. Among all species, the highest value of the examined parameter was obtained for beech wood and pine wood, which were 0.213 (at frequency 3 kHz) and 0.183 (at 6.3 kHz), respectively. The sound velocity decreased for all species only in the tangential direction.

Sound Absorption Coefficient Analysis for Composite Made of Agricultural Waste

The background of this study is to reduce and reuse agricultural waste, specifically rice husk and rice straw waste. This research aimed to determine the sound absorption coefficient / noise absorption coefficient (NAC) of a composite material made of rice husk and rice straw so that it can be used as an alternative acoustic material. Rice husk and straw were processed into composite materials using a polyester matrix with a volume fraction of 30:70 and sample thickness variations of 25 mm and 40 mm. In addition to treating variations in sample thickness, samples were made with different cavity holes diameter variations, including flat (without cavity holes), 3 mm, and 4 mm with 10 mm cavity depth. Samples were tested using a type 4206 impedance tube with two microphones according to the ASTM E1050 standard in the 200 – 1600 Hz frequency range. According to the findings of this study, the maximum sound absorption coefficient value of the rice straw composite material is obtained from samples with a thickness variation of 40 mm and a cavity diameter of 3 mm, with α value of 0.87 at a high frequency of 1,600 Hz. Meanwhile, the rice husk composite material's maximum sound absorption coefficient value was obtained from samples with a thickness variation of 40 mm and a cavity diameter of 3 mm with α value of 0.65 at a low frequency of 400 Hz. According to the findings of this study, rice straw composite material and rice husk composite material have different properties as sound absorbing materials and can be used as acoustic materials in a specific frequency range.

Investigation of Depth Variations of the Bamboo Twigs for its Acoustical Performance

This study aims to determine the relationship between variations in the depth of bamboo twigs with the sound absorption coefficient. The sample consisted of 12 bamboo twigs made up of three types of depth variations. Measurement of sound absorption of bamboo twigs using two microphone impedance tubes and B & K Lab shop software version 16. Standardization ISO 10534-2:1998 [1] was used to test parameters between 100 and 1600 Hz. This type of research is a comparative quantitative approach, data processing using Pulse Lab shop version 16 and visualized into a curve graph using Microsoft Excel. The results showed that the bamboo twig material with a depth of 50 mm was better than 25 mm with an absorption coefficient (α) of 0,68 at a frequency of 1600 Hz. While the material with a thickness of 75 mm only absorbs at a frequency of 1100 Hz with a maximum absorption coefficient of 0,57. According to ISO 11654 [2], it shows that bamboo twigs have the potential to be used as sound-absorbing materials. The sound absorption coefficient value of bamboo twigs rises from low to high frequency with increasing twig depth.

Effects of weaving parameters on acoustic and thermal insulation properties of handmade carpets

Carpeting is one of the most efficient approaches to provide both the acoustic and thermal insulation, and improve the comfort of building inhabitants. In the current research work, the acoustic and thermal properties of handmade carpets as one of the commonly used textile products in several countries, especially in Middle-East countries, have been investigated. Aiming to find the optimum weaving condition to maximize the insulation performance of the handmade wool carpets, the weaving variables of knot type, knot density, and pile height were changed. By performing a set of experiments according to the Response Surface Methodology (RSM), the sound absorption coefficient and thermal resistance values were measured for each sample. The statistical analysis showed that the sound absorption and thermal properties of carpets were appropriately described with the linear model. The pile height was the most effective factor for the both sound absorption and thermal resistance responses. Knot density was marginally significant, while the knot type had a negligible contribution. Increasing the height of the pile and knot density led to an increase in sound absorption and thermal resistance. The optimization procedure suggested that within the experimental range, the best acoustic and thermal insulation, can be obtained at knot density of 35 (per 7 cm), and the pile height of 3 cm.

Study of Physicochemical, Flammability and Acoustic Properties of Hookeri raphia Natural from Cameroon

Introduction: The development of new materials is ultimately associated with requirements such as strength, lightness, low production cost, and raw materials from renewable sources, seeking to meet the needs, research, and development of new technologies, which value the qualification of materials from vegetable sources as natural fibers. Method: In this context, this study aimed to characterize the main physicochemical properties of the natural raffia fiber and its flammability and thermo-acoustic characteristics. These characterizations were performed using several techniques, such as chemical composition analysis, density, moisture adsorption, SEM-EDS, FTIR, and TGA/DTG. Result: The results showed that the morphology of the raffia fiber presents a similar shape to the beehive. The Elemental analysis of the natural fiber of raffia shows that carbon and oxygen contents are predominant, representing a proportion of more than 90%. Furthermore, the results suggest that the fiber is composed of lignin, hemicellulose, cellulose, tannin, and extractives, with cellulose in a proportion of 80%. Conclusion: TGA presents a profile similar to large parts of untreated vegetable fibers. The acoustic test showed excellent sound absorption coefficient (α) values at high frequencies, while the flammability test showed that natural raffia fiber is a good flame retardant.

Conductive Three-Dimensional Lamella Network for Improved Sound Absorption and Heat Transfer

Recently, the quality of life of human has been increasingly threatened by noise caused by various surroundings. To prevent damage from noise, research is being conducted on materials that are capable of both blocking noise in a wide frequency range and transferring frictional heat generated from the noise blocking. In this study, using porous melamine foam (MF) as the basic material, a three-dimensional (3D) lamellar structure with excellent sound absorption and thermal conductivity was manufactured using the dipping process and vapor deposition polymerization, respectively. The 3D lamella structure shows excellent sound absorption performance in a wide frequency range of 250–6300 Hz, and in particular, has a sound absorption coefficient value of 0.96 at 4000 Hz. Due to the coating of the structure using polypyrrole as a conductive polymer, it has a higher thermal conductivity value (0.286 W m–1 K–1) than MF (0.033 W m–1 K–1). This structure also has high structural stability and elastic recovery performance, so it has the same mechanical performance, even after 500 repeated deformations.

Optimization of sound absorbing material by using Taguchi and ANOVA

At present, target on eco-friendly acoustic material is decorated to diminish impact on environment due to adoption of synthetic material in acoustic application. In this paper, Taguchi method is enforced to find optimum parameters for sound absorbing coefficient of coconut fiber-based sound absorbing material. The influence of the various process parameters, i.e. Thickness, density, air gap and fiber percentage (%) on sound absorption coefficient (SAC) was studied. The settings of the parameters were determined by using Taguchi’s experimental design method. Orthogonal arrays (L25) of Taguchi, the signal-to-noise (S/N) ratio, the analysis of variance (ANOVA), and regression analyses were employed to find the optimal process parameter levels and to analyze the effect of these parameters on sound absorption coefficient values. Confirmation test with the optimal levels of parameters was carried out in order to illustrate the effectiveness of the Taguchi optimization method. Optimum parameters were found by using Taguchi method are which have 50 mm thickness, 0.0002539 g/mm3 density, 70% fiber percentage and 0 mm air gap. Also significant parameters are found which are thickness and density having p-value less than 0.05 and followed by fiber percentage and air gap. By using optimum parameters sound absorption coefficient is increased to 0.98 at frequency 2800–3500 Hz.

Contribution of Side Surfaces to the Effectiveness of Automotive Sound-Absorbing Materials

When developing noise-reducing structures for passenger, engine and luggage compartments of motor vehicles, an objective assessment of their sound-absorbing properties is important. The method of measuring the reverberation time of a diffuse sound has found the widest distribution. This method provides sufficient reliability and repeatability of measurement results. However, often the values of reverberation sound absorption coefficient are exceeded relative to the actual values. The article investigates the influence of side surfaces of sound-absorbing materials on equivalent sound absorption. The frequency range of effective absorption by side surfaces is indicated. An updated formula for approximate calculations is given.

Thermal and Acoustic Performance of Green Polyethylene/Cork Composite for Civil Construction Applications

In this study, green high-density polyethylene (GHDPE) composites with 5, 10 and 15% natural powdered cork (CP) with and without 5% maleic anhydride (PE-g-MA) were developed in order to evaluate the potential of these materials for civil construction applications. The composites were produced in a co-rotating twin-screw extruder and injection molded. An impedance tube was used to determine the acoustic behavior of the composites, which were then used as ceiling tiles in prototypes of provisional constructions in order to study ascertain their performance with respect to thermal comfort in the City of Teresina, PI - Brazil. Our data indicates that composites sound absorption coefficient values are good between 500 and 1200 Hz, especially for those with a higher percentage of cork, with the lowest absorption rate observed for composites containing PE-g-MA. The composites used in the prototypes provided a decrease in the internal temperature of the built structure.

Analisis Karakteristik Akustik Dan Dinamik Micro-Perforated Panel Dengan Struktur Honeycomb Mengunakan FEM

This study focuses on the discussion of the correlation of acoustic and dynamic characteristics of hybrid panels, namely Micro-perforated Panel (MPP) and Honeycomb (HC) structures. Acoustic characteristics in experimental studies are obtained by the sound absorption coefficient and Sound Transmission Loss. Meanwhile, the dynamic characteristics are obtained by the mode and frequency response analysis of numerical simulation methods. The results of these two characteristics serve as a benchmark for the development of experimental data studies/analysis. The purpose of this study is to obtain dynamic characteristics using mode and frequency response analysis through the finite element method. The development of this experimental study/analysis data is to overcome the drawbacks of experimental testing. The weakness obtained from experimental studies is that the stages are complicated and require a very large amount of money. The method in this study was carried out by numerical simulation using the finite element method using the Ansys 2019 R3 program. The results of this study obtained dynamic characteristics from the development of experimental study analysis methods using numerical simulations through the finite element method. Numerical simulation on the hybrid panel provides efficiency at the experimental testing stage. The results of the mode and frequency response analysis obtained by numerical simulation methods have similarities in the frequency range of high and low frequency values of sound absorption coefficient and soundtransmission loss.

Desert cotton and areca nut husk fibre reinforced hybridized bio-benzoxazine/epoxy bio-composites: Thermal, electrical and acoustic insulation applications

Due to increasing environmental concerns, significant attention has been gained for seeking out alternative sources for deforestation and to reduce as much as possible for the utilization of petroleum-based chemicals. In the present work hybrid bio-composites have been developed using epoxy resins (DGEBA-isophoronediamine and DGEBA-phenalkamine) and hybridized blend of bio-based cardanol-diaminodiphenylmethane (C-ddm) benzoxazine and DGEBA-isophoronediamine (bio-benzoxazine: epoxy resin 50:50 wt%)reinforced with desert cotton (DC) and areca nut husk fibres (ANF) separately under appropriate experimental conditions, in order to utilize them for high performance thermal, electrical and acoustic insulation panel applications. Mechanical behaviour, thermal conductivity, thermal resistance, electrical surface resistivity, electrical volume resistivity, sound absorption coefficient and sound transmission loss were studied as per standard methods. Results obtained from different studies infer that hybrid blended cardanol benzoxazine composite panels reinforced with desert cotton sandwich areca nut husk fibre (DC-sw-ANHF) possess appreciable thermal resistivity and electrical volume resistivity and the corresponding values are 0.22141 M2 k/w, and 1.888 × 1010 Ω, respectively. Data obtained from acoustic studies, indicate that all the fibre reinforced composites possess more than 0.7 value of sound absorption coefficient at 6400 Hz. The composite panel specimens developed using both desert cotton, and areca nut husk fibre reinforced with hybridized blend of bio-benzoxazine/epoxy resin can be used as insulation materials in the field of building construction.