Search Results (321)

Nowadays, in order to follow the trends and principles of sustainability, natural materials are often investigated in acoustics and noise prevention. Hemp fibre is a sustainable alternative to conventional sound-absorbing or insulating materials. The aim of the research is to investigate the acoustic properties of different types of hemp fibre. Five different types of hemp fibre were tested: bleached, cottonized, boiled cottonized, well-stripped decorticated, and short, not combed decorticated fibres. The hemp fibre samples were varied in thickness from 20, 40, and 60 mm and density from 50 to 250 kg/m³ in steps of 50 kg/m³. The sound transmission loss of the material was measured using an impedance tube. In order to predict the sound absorption properties of the samples, the airflow resistivity of the hemp fibre was determined. Based on the theoretical calculations proposed by Delany, Bazley, and Miki, a theoretical analysis of the sound absorption of hemp fibre was performed. In order to determine the dependence on different fibre types, all fibres were examined using SEM. It has been found that hemp fibre can be used as an insulating or sound-absorbing material in noise prevention, as a sustainable alternative to conventional materials. Full article

Seabed topography exerts a profound influence on underwater acoustic propagation, and the coupling effect between bottom acoustic properties and the source–receiver geometric configuration remains insufficiently quantified, particularly in seamount shielding scenarios. To address this gap, in this study, the BELLHOP ray model was integrated with Earth topography 1 (ETOPO1) topographic data and Hybrid Coordinate Ocean Model (HYCOM) hydrological data for seamounts east of Taiwan. Transmission loss (TL) of 300 Hz sound waves was simulated across four typical bottom types (rock, coarse sand, silt, and clay) under varying source depths (50–1000 m) and receiver depths (50–500 m). The maximum sonar detection range was delineated using an 80 dB TL threshold as the criterion for effective detection. The key findings reveal that the bottom properties are the primary factors that reduce the detection range: the maximum detection range over rock bottom exceeds that over clay by more than 8-fold. Notably, a shallow source–shallow receiver configuration mitigates the acoustic shadow effect induced by seamounts, whereas deep receiver deployment (≥500 m) diminishes the discriminative impact of bottom types on the propagation behavior. Furthermore, a segmented empirical prediction formula was established, which reconciles both the physical mechanisms (e.g., bottom reflection-absorption and seamount shielding) and engineering applicability. This formula provides a robust theoretical basis for evaluating sonar performance in complex seabed topography settings, thereby facilitating optimized underwater detection strategies in seamount-dominated marine environments. Full article

Reducing the consumption of energy-intensive cement and promoting the resource utilization of industrial waste are two critical challenges that should be urgently addressed to achieve the goals of carbon neutrality and green sustainable development in the building materials field. Among these, the massive stockpiling of industrial waste such as fly ash and silica fume poses serious threats to the environment and human health, making their efficient utilization an urgent need to alleviate environmental pressure. This study employs the ice-template method to incorporate fly ash and silica fume as functional components into a cement-based system, fabricating a novel composite material. This material features a layered porous structure, which not only reduces cement usage but also results in a lighter weight. The introduction of the ice-templating method successfully constructed an anisotropic lamellar structure, leading to significant enhancements in flexural strength and toughness—by approximately 26.6% and 30%, respectively, vertical to the lamellae compared to conventional dense cement. Meanwhile, the hybrid blend of silica fume and fly ash effectively improved the deformability of the material, as evidenced by a notable increase in compressive failure strain. These excellent behaviors of mechanical properties are attributed to the formation of a multi-scale microstructure characterized by “macroscopically continuous and microscopically dense” features. Moreover, this specific microstructure offers greater advantages in sound absorption performance. The acoustic impedance tube tests demonstrate that the noise reduction coefficient of the novel cement-based material incorporating fly ash and silica fume is improved by 82%, holding promising applications in noise reduction for the construction and transportation fields. This research provides a feasible pathway for the high-value application of industrial solid waste in low-carbon materials. Full article

To address the issue of sound absorption valleys in open-cell aluminum foam and enhance mid-to-high frequency (800–6300 Hz) performance, we developed a novel pore-penetrating 316L stainless steel fiber–aluminum foam (PPFCAF) composite using an infiltration method. The formation mechanism of the pore-penetrating fibers, the resultant pore-structure, and the accompanying sound absorption properties were investigated systematically. The PPFCAF was fabricated using 316L stainless steel fiber–NaCl composites created by an evaporation crystallization process, which ensured the full embedding of fibers within the pore-forming agent, resulting in a three-dimensional fiber-pore interpenetrating network after infiltration and desalination. Experimental results demonstrate that the PPFCAF with a porosity of 82.8% and a main pore size of 0.5 mm achieves a sound absorption valley value of 0.861. An average sound absorption coefficient is 0.880 in the target frequency range, representing significant improvements of 9.8% and 9.9%, respectively, higher than that of the conventional infiltration aluminum foam (CIAF). Acoustic impedance reveal that the incorporated fibers improve the impedance matching between the composite material and air, thereby reducing sound reflection. Finite element simulations further elucidate the underlying mechanisms: the pore-penetrating fibers influence the paths followed by air particles and the internal surface area, thereby increasing the interaction between sound waves and the solid framework. A reduction in the main pore size intensifies the interaction between sound waves and pore walls, resulting in a lower overall reflection coefficient and a decreased reflected sound pressure amplitude (0.502 Pa). In terms of energy dissipation, the combined effects of the fibers and refinement increase the specific surface area, thereby strengthening viscous effects (instantaneous sound velocity up to 46.1 m/s) and thermal effects (temperature field increases to 0.735 K). This synergy leads to a notable rise in the total plane wave power dissipation density, reaching 0.0609 W/m³. Our work provides an effective strategy for designing high-performance composite metal foams for noise control applications. Full article

Pumice aggregate, with its highly porous structure, offers excellent lightweight and insulating characteristics; however, its excessive water absorption and weak interfacial bonding often limit its mechanical and durability performance in concrete applications. To overcome these drawbacks, this study developed a polymer-coated pumice aggregate (PCPA) concrete by applying a thin polyester layer onto the aggregate surface to enhance matrix–aggregate adhesion and reduce permeability. The mechanical, thermal, and acoustic performances of PCPA were systematically evaluated. Results revealed that polyester coating led to a notable improvement in compressive strength (up to 25%) and significantly reduced weight loss after freeze–thaw cycles. Furthermore, PCPA samples exhibited enhanced resistance to thermal degradation, maintaining structural stability even at 600 °C, and achieved a 40% higher sound absorption coefficient at 630 Hz compared to uncoated pumice concrete. These findings demonstrate that polyester coating effectively addresses the inherent limitations of pumice concrete, offering a promising approach for producing lightweight concretes with superior durability and multifunctional performance. Full article

This study presents a predictive model for estimating the sound absorption coefficient of perforated and non-perforated wooden panels, based on experimental data. Measurements were conducted on four wood species: fir wood (Abies alba), pine wood (Pinus sylvestris), pedunculate oak (Quercus robur), and sessile oak (Quercus petraea) in three panel thicknesses (11 mm, 18 mm and 25 mm), with perforation ratios of 0%, 10%, and 20%. The normal-incidence absorption coefficient was measured using the impedance tube method in accordance with ISO 10534-2. Measurements were performed in a 100 mm impedance tube, selected to match the specimen dimensions; therefore, the analysis is limited to the valid plane-wave frequency range of this tube, between 250 and 1600 Hz. Previous studies have shown that both panel thickness and perforation ratio significantly influence mid- and high-frequency absorption. Our results confirm that increased panel thickness and perforation enhance absorption, consistent with findings reported for micro-perforated and porous wood panels. Based on the measured values, we developed first-order regression functions linking the absorption coefficient to material density, thickness, and perforation percentage. The resulting equations allow reverse estimation of one or more physical parameters to meet target acoustic performance requirements. This data-driven approach provides a practical tool for designing wooden absorbers with predictable behavior and complements existing analytical models for acoustic optimization. Full article

Low-frequency noise, the most critical noise frequency band affecting human physical and mental health, poses a significant challenge for effective control in spatially constrained building environments. The shunt loudspeaker offers a novel solution to control low-frequency noise. Unlike traditional methods, it does not rely on large cavity depth but only requires the adjustment of parameters or structure of the shunt circuit. However, most shunt loudspeakers utilize analog shunt technology, which leads to instability and inaccuracy owing to the negative impedance converter circuit and parasitic impedance in analog electronic components. The paper proposes a tunable low-frequency sound absorber utilizing a combined array of hybrid digital–analog shunt loudspeakers. The theoretical model was established based on the electro-mechanical–acoustic analogy method and parallel impedance method. Numerical simulations and experimental studies were performed to verify the proposed model. The results demonstrate that the proposed absorber can achieve excellent low-frequency sound absorption capability by designing only a few digital filter parameters, while simultaneously enhancing the stability and accuracy of the system. This study presents a promising innovative method for low-frequency noise control at sub-wavelength scales, providing a space-efficient solution. Full article

Accurate prediction of sound propagation in porous and dissipative media remains challenging when classical models struggle to capture the microscopic material characteristics. This work introduces the Enhanced Numerical Equivalent Acoustic Material (eNEAM) framework, extending the original NEAM formulation by combining analytical and numerical approaches. The analytical formulation provides closed-form expressions for effective impedance, complex wavenumber, and absorption coefficient under normal incidence, with and without thermo-viscous effects, enabling a direct validation against impedance-tube data and efficient initialization of finite-difference time-domain (FDTD) simulations. A parameter optimization strategy, focused on the thermolabile coefficient (${\Psi }_B$), significantly improves low-frequency absorption predictions. Robustness studies reveal that even substantial variations in model parameters generally remain within an optimal ±10% range. Additionally, a comparison between models with and without thermo-viscous losses was performed and shows that differences are negligible at macroscopic scales, which can be useful to reduce computational costs. Following computational time reduction, the adaptive mesh refinement technique employed also reduces time costs by over 50% in 1-D FDTD simulations, even without GPU acceleration. Taken together, these developments demonstrate that eNEAM provides a versatile, accurate, and computationally efficient framework for modeling porous materials, bridging experimental characterization, analytical formulations, and numerical simulations while maintaining robustness against parameter variations. Full article

Porous concrete is widely recognized as an eco-friendly pavement material; however, existing studies mainly focus on its use as a base course, and systematic investigations on porous concrete specifically designed for heavy-traffic pavements and multifunctional surface performance remain limited. In this study, a novel multifunctional porous concrete with integrated noise reduction and drainage performance (PCNRD) was developed as a top-layer pavement material, addressing the performance gap in current applications. A comprehensive evaluation of the surface properties of porous concrete was performed based on tests of the sound absorption, void ratio, permeability, and wear resistance. The results demonstrate that the porous concrete exhibits excellent sound absorption (sound absorption coefficient 0.22–0.35) and high permeability (permeability coefficient 0.63–1.13 cm/s), and superior abrasion resistance (abrasion loss ≤ 20%) within an optimized porosity range of 17–23%. Furthermore, an optimized pavement thickness (8–10 cm) was proposed, and functional correlations among key surface performance indicators were revealed for the first time. Based on a uniform experimental design, four key mix parameters (water–cement ratio, cement content, silica fume content, and cement strength grade) were examined using strength and effective porosity as dual control indices, leading to the development of a novel mix design method tailored for PCNRD. This study not only fills the technical gap in high-performance porous concrete for heavy-traffic pavement surfaces but also provides a practical scientific framework for its broader engineering application. Full article

With the increasing demand for sustainable building materials, it has become essential to identify sustainable alternatives to conventional sound absorbers, particularly in the context of waste reduction and the circular economy. The aim of this study was to compile and describe a structured dataset of sound absorption coefficients for laboratory-produced panels made from recycled textile materials. Five types of panels were developed using cotton, polyester, wool, linen, and a mixed composition of textiles. A biopolymer binder was applied to ensure structural stability of the materials. Following careful sorting, shredding, and homogenization of the textile waste, test specimens were prepared and examined under controlled laboratory conditions. The sound absorption coefficients were measured using an AFD 1000 impedance tube in accordance with the ISO 10534-2 standard, across a frequency range from 6.25 to 6393.75 Hz. For each material, three repeated measurements were performed, and mean values were calculated to ensure accuracy and reliability. The resulting dataset contains structured values of sound absorption coefficients, which can be applied in building acoustics modeling, comparative studies with conventional insulation materials, and the development of new sustainable products. In addition, the data can be used in educational contexts and machine learning applications to predict the acoustic properties of recycled textile composites. Full article

This review provides a comprehensive overview of modern experimental and numerical methods for characterizing the sound absorbing properties of dissipative sound-absorbing materials. Experimentally, we summarize both in situ techniques (e.g., pulse reflection, two-microphone, p-u probe, and spatial Fourier transform method) and laboratory methods (e.g., impedance tube, transfer function, and reverberation room methods), discussing their principles and applications. For the numerical methods, we detail the development and refinement of empirical models (e.g., Delany–Bazley, Miki, Komatsu), theoretical models (e.g., Johnson–Champoux–Allard), and computer numerical methods, along with methods for obtaining flow resistivity, including empirical formulas, experimental measurements. Furthermore, we review recent advances in machine learning approaches (e.g., generalized regression neural networks, radial basis function neural networks, and artificial neural networks) for predicting the sound absorption coefficient. This work aims to serve as a methodological reference for the research, development, and performance evaluation of dissipative sound-absorbing materials. Full article

Multi-purpose gymnasiums are typically designed for sport events and large-scale gatherings. However, the gymnasium investigated in this study lacked sufficient consideration of acoustic performance during its design phase, resulting in severe echo problems, long reverberation time and poor speech intelligibility. These acoustic deficiencies limit its ability to host major events, reduce utilization efficiency and cannot be resolved by simply adjusting the sound reinforcement system. Conventional renovation strategies usually involve sound-absorbing materials on walls or ceilings, which are costly, labor-intensive and time-consuming. The case gymnasium discussed in this study has the particular advantage that its ceiling structure already provides partial sound absorption. To lower renovation costs and minimize construction workload, this research builds upon the existing ceiling structure and evaluates five renovation schemes through comparative analysis, proposing a renovation approach that remains economical while providing substantial performance benefits. The study calibrates the acoustic model through comparison between measurement and simulation in ODEON V16.0 software, and the validated model was further used to predict acoustic parameters under full occupancy across different schemes. Post-renovation field measurements confirm the reliability and accuracy of the proposed approach, offering a valuable reference for similar gymnasium acoustic retrofitting projects. Full article

The development of sound-absorbing coatings for underwater structures has attracted significant attention due to their critical role in stealth and noise mitigation. While much of the recent research has focused on novel materials and complex configurations, the present study adopts a fundamentally different approach by establishing theoretical bounds on acoustic absorption that are independent of specific designs. Assuming only linearity and viscous damping, we model coatings using discrete mechanical elements characterized by mass, stiffness, and damping parameters. These models incorporate practical design constraints on added mass and hydrostatic compression of the coating. To identify configurations that maximize average acoustic absorption over a frequency range, we employ a Particle Swarm Optimization Algorithm that performs a global search over the constrained parameter space. A method for constraining the search space, which can be extended to any optimization algorithm, is presented and illustrated by examples. Perhaps surprisingly, our findings reveal that complex topologies yield only marginal performance gains compared to simpler configurations. For the canonical mass-spring-damper model, we derive closed-form approximations for absorption in the low-, mid-, and high-frequency regimes. These results establish performance ceilings for each topology, providing a benchmark for evaluating and guiding future material and structural innovations in underwater acoustic coatings. Full article

Inspired by the concept of antennas in electromagnetics, this study proposes a novel acoustic metamaterial using Archimedean spiral structures. Unlike traditional resonant absorption structures, the present structure does not rely on resonant cavities but consists of multiple channels bent according to specific geometric parameters. The absorption mechanism is attributed to the combination of Fabry–Pérot (FP) resonance and viscous loss effects at waveguide boundaries. A theoretical model based on the transfer matrix method has been established and validated through numerical methods. Furthermore, the present study investigated the relationship between absorption performance and geometric parameters through theoretical analysis and numerical simulations, achieving efficient absorption across a wide frequency range and at low frequencies by adjusting these parameters. Additionally, samples have been fabricated using additive manufacturing techniques and experimental validation confirmed the accuracy of the theoretical and numerical simulations. The structure designed in this paper is expected to be applied to the engineering field with the need of broadband sound absorption. Full article

Nanofibers, with their lightweight structure and superior sound absorption, are promising materials for noise control in automotive and architectural applications. However, due to the complex porous structure of nanofibers, established acoustic models often fail to accurately quantify the microstructure’s influence on sound absorption characteristics, resulting in substantial prediction errors. To determine the sound absorption characteristics of nanofibers, an equivalent fiber network model was developed using the multiscale finite element analysis (MFEA) method based on SEM images of nanofibers. The slip boundary condition (SBC) was then applied to calculate the microstructural parameters necessary for macroscopic characterization. The sound absorption coefficients of nanofibers were characterized using three acoustic models, and the results were compared with the experimental data. The predictions of the Limp frame model agreed well with the experimental data within the 500–6400 Hz frequency range. Through use of the multiscale model developed in this study, a deterministic relationship between microstructure and acoustic properties was established, revealing that the inertial interactions between sound waves and the nanofiber skeleton, as well as the slip boundary effect at the nanofiber surfaces, are among the primary mechanisms contributing to the flow resistance and superior sound absorption performance of nanofibers. Full article