Sound Absorption Properties Research Articles

Sustainable sound absorption using shredded plastic particles: Adjusting low-frequency acoustic performance with particle size

This study investigates the sound absorption properties of shredded recycled plastic particles, with a focus on how particle size influences low-frequency acoustic performance. Given the growing environmental challenge posed by plastic waste, this research aims to repurpose such materials into effective, sustainable sound absorbers, contributing to both noise reduction and waste minimization efforts. The sound absorption coefficients and normalized surface impedances of different size fractions, ranging from 45 µm to 3 mm, were measured using the standard two-microphone impedance tube method in accordance with ISO 10534-2. The analysis revealed that smaller particle sizes significantly enhance low-frequency absorption, though at the expense of the maximum absorption coefficient across a broader frequency range. This trade-off underscores the importance of particle size in designing materials tailored to specific acoustic applications. Results indicate that optimal sound absorption shifts towards higher frequencies for larger particle sizes, while finer particles are more effective at lower frequencies. The ability to customize the acoustic properties of shredded plastic particles by selecting appropriate particle sizes is a key outcome of this study. Microscopic examination of the particles revealed a correlation between particle morphology and acoustic performance, with irregular shapes contributing to enhanced sound energy dissipation. The findings suggest that shredded recycled plastic particles are a viable and sustainable option for creating customizable sound-absorbing materials, particularly in applications where low-frequency noise reduction is critical. This research not only advances the understanding of acoustic performance in recycled materials but also supports broader sustainability goals by offering an innovative use for plastic waste in industrial and architectural noise control solutions. In conclusion, this study provides a foundation for the development of eco-friendly, effective sound-absorbing materials from recycled plastics, emphasizing the importance of particle size in achieving desired acoustic properties.

POLYESTER APPAREL CUTTING WASTE AS SOUND INSULATION MATERIAL

This study developed an insulation structure using waste from apparel cutting and examined its sound insulation capabilities. Shredded polyester apparel cuttings served as the primary material for this structure. Results indicate that the insulation made from apparel waste exhibits superior sound absorption properties compared to conventional sound and thermal insulators. The average sound absorption ranged from 54.7% to 74.7% across frequencies from 250 to 2000 Hz. This research proposes a method to reduce environmental pollution by repurposing polyester apparel waste for insulation in roofs and internal walls.

Acoustic, Mechanical, and Thermal Characterization of Polyvinyl Acetate (PVA)-Based Wood Composites Reinforced with Beech and Oak Wood Fibers.

Considering the growing need for developing ecological materials, this study investigates the acoustic, mechanical, and thermal properties of wood composites reinforced with beech or oak wood fibres. Scanning electron microscopy (SEM) revealed a complex network of interconnected pores within the composite materials, with varying pore sizes contributing to the material's overall properties. Acoustic characterization was conducted using a two-microphone impedance tube. The results revealed that the fibre size significantly impacts the sound absorption coefficient, demonstrating that the highest sound absorption coefficient of 0.96 corresponds to the composites reinforced with oak wood fibres with a size of 2 mm in the low-frequency range of 1000-2500 Hz. Mechanical testing revealed a significant reduction in compressive strength as fibre size increased from 0.4 mm to 2 mm, correlating with the observed changes in sound absorption and thermal properties. Thermal analysis indicated thermal conductivity (λ) values ranging from 0.14 to 0.2 W/m·K, with a notable increase in conductivity as fibre size decreased. It was shown that composites reinforced with beech or oak wood fibres with a size of 2 mm are recommendable for insulation materials due to the lowest thermal conductivity of 0.14 W/(m·K). Oak wood composites with a fibre size of 0.4 mm recorded the highest heat capacity, which is 54.4% higher than the one corresponding to the composites reinforced with the largest fibres. The results regarding heat diffusion rates are also reported. The findings about the effects of fibre size and pores on thermal, acoustic and mechanical properties provide valuable insights for designing sustainable materials, offering potential applications in industries where balanced performance across multiple properties is required.

Comparison of the Influence of Polypropylene (PP) or Polybutylene Terephthalate (PBT)-Based Meltblown and Polyester/Polyamide-Based Hydroentangled Inner Layers on the Sound and Thermal Insulation Properties of Layered Nonwoven Composite Structures.

Thermal and sound insulation play a vital role in today's world, and nonwoven composite structures including microfiber layers provide efficient solutions for addressing these demands. In this study, the sound and thermal insulation properties of nonwoven composite structures, including single-layer meltblown, multilayer meltblown, hydroentangled, and nanofiber nonwoven inner layers, were compared statistically by using Design Expert 13 software. The inner layer type and outer layer type of the composite structures were considered as independent variables, and thickness, bulk density, air permeability, sound absorption coefficient, and thermal resistance of composite structures were evaluated as dependent variables during statistical analyses. The effects of layer types on dependent variables were investigated comparatively, and the best inner and outer layers for high sound and thermal insulation were determined. It was concluded that the developed nonwoven composites including hydroentangled and three-layered meltblown layers demonstrated superior sound absorption properties at low (changing between 48% and 70%) and moderate (ranging between 77% and 96%) sound frequencies, respectively, when compared to composites and materials including single-layer meltblown or nanofiber nonwoven structures reported in prior studies. Additionally, it can be inferred that the composite structures obtained in this study exhibited thermal resistance properties (0.49 to 0.73 m2K/W) comparable to those of commercial thermal insulation materials.

Investigation of factors affecting the sound absorption behaviour of 3D printed hexagonal prism lattice polyamide structures

The aim of this work is to investigate the sound absorption properties of open-porous polyamide 12 (PA12) structures produced using Selective Laser Sintering (SLS) technology. The examined 3D-printed samples, fabricated with hexagonal prism lattice structures, featured varying thicknesses, cell sizes, and orientations. Additionally, some samples were produced with an outer shell to evaluate its impact on sound absorption. Experiments were conducted using the transfer function method with an acoustic impedance tube in the frequency range of 250 Hz and 6400 Hz. The results showed that the studied geometric factors significantly affected the sound absorption of the PA12 samples. In some cases, the hexagonal prism lattice structures demonstrated relatively high sound absorption properties. Thanks to their properties such as lower weight, recyclability, and resistance to moisture and chemicals, these structures become competitive with commonly used sound-insulating materials, making them promising candidates for sound absorption. Furthermore, numerical simulations using Ansys software confirmed that the sound absorption properties of the open-porous material structures generally increased with higher specific airflow resistance. The findings highlight the advantages of 3D printing technology in producing complex, highly customizable porous structures for noise reduction applications.

Eco-Friendly, Sound Absorbing Materials Based on Cellulose Acetate Electrospun Fibers/Luffa Cylindrica Composites.

Sound absorption plays a crucial role in addressing noise pollution that may cause harm to both human health and wildlife. To tackle this environmental issue, the implementation of natural-based sound absorbing materials attracts considerable attention in the last few years. In this study, sound absorbing, eco-friendly composites are produced by combining a 3D natural sponge namely Luffa Cylindrica (LC) with cellulose acetate (CA) microfibrous layers that are fabricated through electrospinning. Electrospun microfibers can effectively absorb sound waves due to their unique properties such as high porosity, small diameter, and large surface area. The individual components and the resulting composites, exhibiting various configurations, are characterized in respect to their morphology, porosity, density, and sound absorption properties. More precisely, the sound absorption coefficient is determined through the standing wave ratio method within the range of 500-4000 (Hz) frequency. The most promising materials consist of a multilayer combination of LC with CA microfibrous layers, which creates new prospects in the development of such materials for sound absorption applications.

Preparation of polymer hollow microsphere filled epoxy resin-based syntactic foam material and its performance analysis

To explore sound-absorbing and flame-retardant materials that meet the requirements for double-shielded and double-insulated Faraday cages, polymethyl methacrylate (PMMA) microspheres were incorporated into epoxy resin-based syntactic foam materials for testing and analysis. The addition of PMMA microspheres was found to enhance the electrical, mechanical, sound-absorbing, and flame-retardant properties of the syntactic foam, providing a potential reference for applications in high-voltage hall shielding and sound absorption. Syntactic foams with four concentrations of PMMA microspheres (0%, 0.5%, 1%, and 2%) were prepared. High-voltage breakdown testing, impedance tube testing for sound absorption coefficient, cone calorimetry for flame-retardant performance, and tensile and bending tests were conducted. Results showed that as the concentration of PMMA microspheres increased, improvements were observed in the tensile, bending, flame-retardant, and sound absorption properties of the syntactic foams, while breakdown strength decreased. These findings provide valuable insights into the application of syntactic foam materials in double-insulation, double-shielded Faraday cages.

Cellulose-Based Acoustic Absorber with Macro-Controlled Properties

Cellulose-based materials are now commonly used, including in the field of acoustic comfort. Often presented as a less environmentally impactful alternative to traditional acoustic absorbents (such as melamine, glass wool, etc.), these cellulose-based materials are more frequently derived from recycling, undergoing, in most cases, a technical process that allows these cellulose fibers to be obtained, thus inheriting the acoustic properties of the latter, with limited or even non-existent control. This paper proposes a manufacturing process that allows for the production of cellulose foam with precise control over its porosity, pore size, and interconnections. In addition to exhibiting good sound absorption properties, this process also enables the fabrication of gradient-porous structures and other hybrid materials, which can result in remarkable sound absorption properties.

Design, Preparation, and Analysis of the Acoustic Performance of Waste Hemp/PLA Fiber Sound-Absorbing Composites with Different Bionic Structures

Noise pollution is becoming more and more serious, and the environmental friendliness of building materials could be better. To solve these problems, waste hemp fibers were used as reinforcement and polylactic acid (PLA) fibers as matrix. Sustainable biodegradable sound-absorbing composites with different bionic structures were prepared by carding and hot press molding process. The sound absorption properties of bionic structural composites with smooth surface,triangular wedge surface, trapezoidal prismatic surface, sinusoidal wave surface,cylindrical pit surface, and rectangular raised surface were tested. Composites were 30mm in thickness and 100mm in diameters.The bionic sound structure models was constructed according to the extracted bionic structure. The sound performance of the sound-absorbing composites was analyzed by finite element method simulation. The effects of bionic structure and sound characteristic parameters on the sound absorption performance of the composites were investigated and the sound absorption mechanism of the sound composites with bionic structures was revealed. Then the model of the cylindrical pit surface was used as a research object further to optimize the sound absorption performance. The results revealed that the optimized bionic structural composite materials had a sound absorption performance grade of II, with a sound absorption average (SAA) coefficient in the mid-frequency range of 27.16% higher than that of the smooth surface composites. The noise reduction coefficient was 0.603, and the SAA coefficient was 0.583.The results not only find a new way to recycle the waste hemp fibers, but also provide an experimental basis and theoretical basis for the optimization of sound absorption composites in building applications.

The Sound Absorption Performance of Laser-Sintered Composite Biomimetic Wood Porous Structures.

This study investigates the development of biomimetic sound-absorbing components through laser sintering technology, drawing inspiration from wood's natural porous structure. Using a pine wood powder/phenolic resin composite, various specimens were fabricated with different structural configurations (solid, fully porous, and varying straight-pore ratios) and cavity thicknesses. Sound absorption performance was evaluated using the impedance tube transfer function method. The effect of different composite structures, placement orientations, and cavity thicknesses on sound absorption performance was evaluated. The results demonstrate that solid laser-sintered samples exhibit inherent sound absorption properties due to microscopic pores, with absorption coefficients exceeding 0.234. The biomimetic wood-like structure, featuring multi-scale porosity at both microscopic and mesoscopic levels, shows enhanced broadband sound absorption, particularly in mid-high frequencies, with characteristic double-peak absorption curves. The study reveals that absorption performance can be optimized by adjusting structural parameters and thickness, enabling targeted frequency-specific sound absorption. This research establishes the feasibility of creating multi-frequency sound-absorbing materials using laser-sintered biomimetic wood structures, providing a foundation for future applications and development in acoustic engineering.

Multifunctional acoustic and mechanical metamaterials prepared from continuous CFRP composites.

The imperative advance towards achieving "carbon neutrality" necessitates the development of porous structures possessing dual acoustic and mechanical properties in order to mitigate energy consumption. Nevertheless, enhancing various functionalities often leads to an increase in the structural weight, which limits the feasibility of using such structures in weight-sensitive applications. In accordance with the outlined specifications, a novel structural design incorporating carbon fiber reinforced polymer (CFRP) composites alongside mechanical and acoustic metamaterials has been introduced for the first time. This innovative construction exhibits a lightweight composition with excellent mechanical and acoustic characteristics. Experimental findings demonstrate that with meticulous planning and fabrication, CFRP composite structures can achieve a balance of lightweight construction, high strength, exceptional energy absorption, and remarkable resilience. By introducing membrane and reasonable cavity design, the structure can produce low broadband noise reduction performance by a local resonance effect and impedance matching mechanism of metamaterials. The structural sound insulation capability breaks traditional mass law, resulting in an exceptionally broadband sound insulation peak (bandwidth of nearly 1000 Hz). Furthermore, the sound absorption characteristic of the structure surpasses that of the melamine sponge at frequencies below 300 Hz, demonstrating superior low-frequency sound absorption properties. The proposed structure provides new approaches for the design of multifunctional lightweight superstructures.

Identification of Mechanical and Sound Absorption Properties of Porous Concrete Containing Different Amounts of Palm Oil Clinker

Palm oil clinker (POC) is an industrial waste by-product of the palm oil industry that is usually dumped into landfills. This paper identified the mechanical and sound absorption properties of porous concrete (PC) when different amounts of porous POC aggregates were used. In addition, an ultrasonic pulse velocity (UPV) test was performed to explain the specimen porosity which affected the properties of concrete. POC with a size of 2.36 mm – 6.7 mm was used at 25%, 50%, 75%, and 100% as a substitute for river sand. Compressive strength, density, and UPV decreased as the percentage of POC increased. Replacement of 100% POC reduced the strength by 62%, density by 30%, and UPV by 16% as compared to without POC. A reduction in the UPV value indicated an increase in the porosity of concrete due to the macropores in POC aggregates. The highest improvement of 673% in average sound absorption coefficient for 100% POC as compared to PC which used sand at 250 Hz – 1250 Hz for 75 mm specimen thickness. Compressive strength data showed that specimens with 100% POC exceeded the minimum limit fora PC barrier layer. Therefore, 100% POC with 75 mm thickness had the potential to be applied as a barrier component.

Optimization of sound absorption of recycled Nylon fibrous materials

A semi-empirical model for the assessment and an optimization procedure of the sound absorption coefficient of compressed nonwoven fibrous materials made from recycled Nylon fibers (RNF) is developed. In general, the prediction of the sound absorption properties of materials requires the measurement of non-acoustic parameters by specialized characterization tools that are not always within reach of most laboratories. The objective of the proposed model is to establish empirical relationships between these non-acoustic parameters and the bulk density of RNF materials. These empirical relationships are then substituted into a conventional acoustic model for porous materials, namely, the model of Johnson-Champoux-Allard. The proposed model accurately predicts the sound absorption coefficients of compressed RNF materials based solely on bulk density, thickness, and frequency. This prediction is validated through impedance tube measurements. Moreover, the model is used with a proposed optimization producedure to identify the ideal density and thickness for maximum sound absorption at a specific frequency. Impedance tube measurements on optimized configurations confirm the effectiveness of this optimization process.

Multifunctional composite paper fabricated by graphene oxide/tannin decorated carbon fiber with excellent electromagnetic interference shielding, antibacterial and sound absorption properties

Considering the distinctive oxidative coupling characteristic of tannin acid, it was used as an interfacial interlayer to build a nano-coating structure on the surface of carbon fiber (CF)using amino-modified graphene oxide (GON) via Schiff base reaction. Furthermore, a kind of multifunctional composite paper (PTCF/GON) with excellent electromagnetic interference shielding, antibacterial and sound absorption properties was fabricated using surface modified CF (TCF/GON) and plant fibers. The increased active groups on the surface of TCF/GON improved its hydrophilicity and enhanced its dispersibility in water, which facilitated to form an effective interconnected conductive network of composite paper via traditional wet forming process. Composite paper fabricated by 30 wt% surface decorated CF (PTCF1.5/GON1.2) achieved an electromagnetic interference shielding effectiveness as high as 43.4 dB in X-band, shielding 99.9 % of incident electromagnetic energy. Meanwhile, PTCF1.5/GON1.2 exhibits good sound absorption performance in specific frequency bands, with a sound absorption coefficient of 0.98 around 1180 Hz. Besides, PTCF1.5/GON1.2 also exhibited excellent antibacterial properties. This strategy provides an economical and practical method for manufacturing multifunctional electromagnetic shielding materials with superior performance.

Study on the sound absorption characteristics and noise reduction mechanism of coconut-shell-activated carbon particles and coconut fiber composite biomass sound-absorption materials

Abstract Sound-absorbing materials are widely used in the field of automotive industry. Biomass materials are abundant in the nature, some of which have natural sound absorption and noise reduction properties. Biomass sound-absorption materials are green and pollution-free, which have obvious noise reduction effect on middle- and high-frequency noises, a large specific surface area, a light weight and strong sound absorption effect. The purpose of this paper is to prepare new types of biomass composite sound absorbing material. In order to analyze the sound absorption and physical properties of biomass sound-absorbing materials, the noise reduction performance of different structures of biomass sound-absorbing materials was analyzed. In this paper, the biomass sound-absorbing materials coconut-fiber- and coconut-shell-activated carbon particles were used to make samples. A coconut-shell-activated carbon sound-absorption material (CSAC) was made. The cylindrical holes were made and filled with coconut fiber materials to form composite sound-absorbing materials (CSAC-F). The acoustic performance of an impedance tube was tested based on the acoustic absorption coefficient, whose physical performance was studied by means of a scanning electron microscope (SEM), Brunauer, Emmett and Teller (BET), x-ray diffraction (XRD), a Fourier transform infrared spectrometer (FTIR), thermogravimetric analyzer (TGA) and other detection methods. In contrast, the sound absorption effect of CSAC-F was better in the middle- and low-frequency range, whose microstructure was analyzed and its mechanism of noise reduction was studied. This study will provide a new way for the research and development of sound-absorbing materials in the automotive industry, and biomass sound-absorbing materials have potential applications in the noise absorption and vibration control of automotive interior.

Development and validation of a new asphalt mixture to reduce tyre-road contact noise in interurban areas

Road transport is one of the most important sources of noise emissions having a serious impact on human health. Thus, the objective of this study is to develop an innovative asphalt mixture that decreases noise from tyre and pavement interaction on highways with average speeds of about 80 km/h. To achieve this, a series of mechanical and functional tests were conducted both in the laboratory and at the Gustave Eiffel University Accelerated Pavement Testing (APT) facility. The new experimental mixture achieves a balance between high void content and low macro-texture (wavelengths of 5–50 mm), which improves noise reduction while maintaining good mechanical performance. This is achieved thanks to its two-layer structure, with a top layer of reduced maximum aggregate size (4 mm) and a thickness suitable for optimum sound absorption. Various mechanical tests, including the particle loss test and the water sensitivity test, along with functional evaluations focusing on texture, flow resistivity and sound absorption properties, were performed. Measurements on the APT were taken at three different stages of the pavement service lifetime during the testing phase. The outcome was the production of an asphalt mixture that reduced noise up to 6.8 dB in comparison to an asphalt concrete road.

Influence of variable sound-absorbing devices on room acoustical parameters of reverberation and intelligibility in medium-to-large multipurpose halls.

Multipurpose halls are designed to host various performances. However, achieving the ideal reverberation time (RT) for each of the different performance types can be challenging. This study investigates five halls of various sizes to determine the effects of sound-absorbing devices on variable RTs in multipurpose halls. The composition and sound absorption properties of the finishing materials were investigated in areas where sound-absorbing devices were not applied. Further, the changes in the room acoustic parameters of these medium-sized multipurpose halls were analyzed using computer-based acoustic simulations to find a suitable answer among the various solutions tested. By applying sound-absorbing devices (resonant-type) to 25% of the walls and ceilings of the target halls, the absorption and reflection modes displayed a variability range of more than 0.5 s in the bass-mid frequency (250-500 Hz). However, a variable range of 0.18 s was found in the high frequency (2000 Hz). To improve the low variable range in the high frequency, a partial application of a high-frequency high-performance sound absorption banner (porous-type) was used to secure a variable range of 0.35 s in the high frequency. Variable sound-absorbing devices should be considered to achieve effective RT variation for all frequencies.

Multifunctional ANF/ CNT/FCIP aerogels with superior sound and electromagnetic wave absorption and mechanical properties

Aerogels exhibit bright prospect for multifunctional applications in noise reduction, radar stealth, load bearing, etc. Existing aerogels however suffer from poor sound absorption at low frequencies, narrow-band electromagnetic wave absorption and low structural strength. Here, we propose a novel lightweight aerogel composed of aromatic polyamide nanofiber (ANF)/ carbon nanotubes (CNT)/ flake carbonyl iron powder (FCIP) to boost acoustic/electromagnetic absorption and mechanical performance simultaneously. The FCIP additives create surface roughness and enlarge the pore size of the aerogel. As a result of the enhanced viscous energy dissipation by surface roughness and better impedance match achieved due to the enlarged pores, sound absorption at low frequency is significantly improved. Besides, the electrically and magnetically conductive network generated by embedded FCIP brings about effective electromagnetic absorption covering the whole X-band. Moreover, the aerogels undergo an increase in skeleton thickness and pore size by FCIP, resulting in maximum compressive stress increment. Our study provides clear guidance for the performance enhancement of aerogels that advances the development of aerogels for multifunctional applications.

Synthesis of Highly Porous Graphene Oxide-PEI Foams for Enhanced Sound Absorption in High-Frequency Regime.

High-frequency noise exceeding 1 kHz has emerged as a pressing public health issue in industrial and occupational settings. In response to this challenge, the present study explores the development of a graphene oxide-polyethyleneimine (GO-PEI) foam (GPF) featuring a hierarchically porous structure. The synthesis and optimization of GPF were carried out using a range of analytical techniques, including Raman spectroscopy, scanning electron microscopy (SEM), Braunauer-Emmett-Teller (BET) analysis, X-ray diffraction (XRD), and Fourier-transform infrared spectroscopy (FT-IR). To evaluate its acoustic properties, GPF was subjected to sound absorption tests over the 1000-6400 Hz frequency range, where it was benchmarked against conventional melamine foam. The findings demonstrated that GPF with a GO-to-PEI composition ratio of 1:3 exhibited enhanced sound absorption performance, with improvements ranging from 15.0% to 118%, and achieved a peak absorption coefficient of 0.97. Additionally, we applied the Johnson-Champoux-Allard (JCA) model to further characterize the foam's acoustic behavior, capturing key parameters such as porosity, flow resistivity, and viscous/thermal losses. The JCA model exhibited a superior fit to the experimental data compared to traditional models, providing a more accurate prediction of the foam's complex microstructure and sound absorption properties. These findings underscore GPF's promise as an efficient solution for mitigating high-frequency noise in industrial and environmental applications.

Utilizing polydispersity in three-dimensional random fibrous based sound absorbing materials

The distribution of fiber diameters plays a crucial role in the transport and sound absorbing properties of a three-dimensional random fibrous (3D-RF) medium. Conventionally, volume-weighted averaging of fiber diameters has been utilized as an appropriate microstructural descriptor to predict the static viscous permeability of 3D-RF media. However, the long wavelength acoustical properties of a 3D-RF medium are also sensitive to the smallest fibers, this is particularly true in the high-frequency regime. In our recent research, we demonstrated that an inverse volume-weighted averaging of fiber diameters can effectively serve as a complementary microstructural descriptor to capture the high-frequency behavior of polydisperse fibrous media. In the present work, we reexamine the identification of two representative volume elements (RVEs) which relies on the reconstruction of 3D-RF microstructures having volume-weighted and inverse-volume weighted averaged fiber diameters, respectively in the low-frequency and high frequency regimes. We investigate the implication of such a weighting procedure on the transport and sound absorbing properties of polydisperse fibrous media, highlighting their potential advantages. Furthermore, we discuss the challenges associated with this research field. Finally, we provide a brief perspective of the future directions and opportunities for advancing this area of study.