Search Results (160)

Electric propulsion motors are more efficient than internal combustion engines, but they generate high-frequency tonal noise, which can be perceived as annoying. Acoustical materials are typically suitable for high-frequency noise, making them ideal for acoustic noise mitigation. This paper investigates the effectiveness of three acoustical materials, namely, 2″ Polyurethane foam, 2″ Vinyl-faced quilted glass fiber, and 2″ Studiofoam, in mitigating the acoustic noise from an induction motor and a variable frequency inverter. Acoustic noise rates at multiple motor speeds, with and without the application of acoustical materials, are compared to determine the effectiveness of acoustical materials in mitigating acoustic noise at the transmission stage. Acoustical materials reduce acoustic noise from the induction motor by 5–14 dB(A) at around 500 Hz and by 22–31 dB(A) at around 10,000 Hz. Among the tested materials, Studiofoam demonstrates superior noise absorption capacity across the entire frequency range. Polyurethane foam is a cost-effective and lightweight alternative, and it is equally as effective as Studifoam in mitigating high-frequency acoustic noise above 5000 Hz. Full article

The development of new sound absorbing materials and the transition to net zero emissions production have become inseparable. This paper investigates a new type of composite sound absorbing material made of waste tyre textile fibre (WTTF) and different binders: polyurethane resin (PU), polyvinyl acetate (PVA), and starch (POS). Non-acoustic and acoustic parameters were studied, and life cycle assessment was performed for the considered composite sound absorbing materials. The airflow resistivity was determined according to the ISO 9053-1 standard, while the sound absorption coefficient was determined according to the ISO 10534-2 standard, and the LCA was performed based on the ISO 14040 and ISO 14044 standards. Composite sound absorbing materials subjected to sound absorption coefficient tests showed results in the range of 0.04 to 0.99 and peaking in the frequency range of 800 to 2000 Hz, while airflow resistivity varied between 17.4 and 83.6 kPa⋅s/m². The combination that gave the highest sound absorption coefficient was experimentally found to be PU composite material. Life cycle assessment results revealed that the lowest potential impact on the environment is obtained when composite materials are produced using starch as a binder and its total potential impact on the environment varied between 0.27 and 0.55 Pt, while the highest potential impact was observed by PU composites (0.33 ÷ 0.64 Pt). The results obtained experimentally and by LCA modelling revealed great attractiveness and promising development of composites using WTTF and different binders’ potential for sound absorbing applications. Full article

Porous sound absorption ceramic is one of the most promising materials for effectively eliminating noise pollution. However, its high production cost and low mechanical strength limit its practical applications. In this work, low-cost and in situ mullite whisker-reinforced porous sound-absorbing ceramics were prepared using recyclable construction waste and Al₂O₃ powder as the main raw materials, and AlF₃ and CeO₂ as the additives, respectively. The effects of CeO₂ content, AlF₃ content, and sintering temperature on the microstructure and properties of the porous ceramics were systematically investigated. The results showed that a small amount of CeO₂ significantly promoted the growth of elongated mullite crystals in the resultant porous ceramics, decreased the growth temperature of the mullite whiskers, and significantly increased the biaxial flexural strength. When 2 wt.% CeO₂ and 12 wt.% AlF₃ were added to the system, mullite whiskers were successfully obtained at a sintering temperature of 1300 °C for 1 h, which exhibited excellent properties, including an open porosity of 56.4 ± 0.6%, an average pore size of 1.32–2.54 μm, a biaxial flexural strength of 23.7 ± 0.9 MPa, and a sound absorption coefficient of >0.8 at 800–4000 Hz. Full article

Sustainability in construction is a growing concern due to the significant polluting waste generated before, during, and after a building’s life cycle. The use of natural materials can significantly reduce the environmental footprint in obtaining, manufacturing, transportation, execution, use, maintenance, and demolition of the building, especially when locally sourced. Natural fibers, in particular, can be used in room acoustics, offering good acoustic absorption while meeting sustainability goals. The objectives of this paper are to evaluate cabuya fiber, grown in Ecuador, as an acoustic absorbing material and to introduce a novel approach using machine learning to simulate the material’s acoustic properties. Eight samples of cabuya fiber, bound with a solution of water and Ca(OH)₂, were prepared with thicknesses between 12 and 30.6 mm. The sound absorption coefficients (SACs) were calculated using an impedance tube, following international standards. A Gaussian regression model was built for the predictions. The results showed that the 30.6 mm sample achieved maximum absorption coefficients of 0.91 at 2 kHz and 0.9 at 5 kHz. The model predictions are very accurate, with a mean square error of just 0.0002. These findings offer valuable insights into using cabuya fiber and advanced predictive models to enhance building acoustic performance and reduce environmental impact. Full article

This article presents a metal matrix composite material consisting of NiTi wires embedded in nitrile butadiene rubber (NBR) that preserves NBR’s inherent acoustic characteristics while enabling acoustic modification through the NiTi phase transition induced by stress and temperature. The macroscopic mechanical parameters of transversely isotropic NiTi-NBR composite materials are derived by means of a secondary bridging model that takes into account interfacial phases. On this basis, the acoustic impedance properties and absorption coefficient of composite materials were examined as a function of NiTi volume fraction using the transfer matrix method. The accuracy and effectiveness of the theoretical method were verified by comparing the calculated results with finite element simulation. The research results indicated that regulating the volume fraction of NiTi can lead to the anticipated value of the input impedance of composite materials, improving impedance matching with media like water and rubber, which offers novel insights and a theoretical foundation for the development of underwater sound-absorbing materials. Full article

This study investigates lightweight and efficient candidates for sound absorption to address the growing demand for sustainable and eco-friendly materials in noise attenuation. Juncus effusus (JE) is a natural fiber known for its unique three-dimensional network, providing a viable and sustainable filler for enhanced sound absorption in honeycomb panels. Microperforated-panel (MPP) honeycomb absorbers incorporating JE fillers were fabricated and designed, focusing on optimizing the absorber designs by varying JE filler densities, geometrical arrangements, and MPP parameters. At optimal filling densities, the MPP-type honeycomb structures filled with JE fibers achieved high noise reduction coefficients (NRC) of 0.5 and 0.7 at 20 mm and 50 mm thicknesses, respectively. Using an analytical model and an artificial neural network (ANN) model, the sound absorption characteristics of these absorbers were successfully predicted. This study demonstrates the potential of JE fibers in improving noise mitigation strategies across different industries, offering more sustainable and efficient solutions for construction and transportation. Full article

The automotive industry is rapidly advancing toward the electrification of vehicles. Battery electric vehicles present unique challenges in heat and noise control due to the absence of an internal combustion engine. These challenges arise from the stringent operating temperature requirements of batteries and the distinct characteristics of their power sources, such as differences in rpm and mounting positions compared to traditional engines. To address these issues, porous sound-absorbing materials and porous insulation materials are commonly employed. Conversely, there is an increasing demand for materials that are both lightweight and compact yet capable of providing excellent sound absorption and thermal insulation. Although porous sound absorbers and insulators are similar, they differ in the microstructure required to achieve high performance, specifically in the size and connectivity of their fluid phases. This increases the challenge of integrating superior sound absorption and insulation properties within the same material. In this study, computational microstructure modeling was employed to develop a non-woven fabric composed of flattened ellipsoidal particles with nanoporosity. This innovative material demonstrates exceptional thermal insulation and sound absorption characteristics attributable to its nanoporosity and high tortuosity. Full article

In recent years, multi-functional lecture halls have developed rapidly and become a symbol of contemporary public spaces and places. This kind of spatial facility that brings together the advantages of land intensiveness and multi-functional integration also faces feedback such as poor acoustic effects. However, current research rarely involves the architectural design perspective, which is actually the root consideration of this problem; that is, how to set up corresponding spatial layout measures to optimize acoustic performance in a relatively economical and simple way. This study uses the academic lecture hall of the School of Architecture and Planning of Yunnan University as a case to try to solve these problems. The research is based on holistic considerations, starting from site selection, architectural design, aesthetic considerations, and environmental noise assessment, and combining simulation results with actual measurement results. Using a prediction–comparison–verification method, key acoustic parameters such as speech intelligibility, loudness, and reverberation time were calculated and evaluated to understand the acoustic design problems of the hall. The study found that the out-of-control reverberation time was the main cause of poor acoustic feedback, and based on this, optimization and transformation were carried out from an architectural perspective. Finally, a renovation suggestion was made that the application of sound-absorbing materials on the rear wall can achieve better acoustic effects inside the hall. Among the space combination methods, the combination of “rear wall, central ceiling, and front ceiling” has the best effect. Practical insights are provided for improving the acoustic performance of the multi-functional lecture halls while taking into account the acoustic design and feasible requirements. Full article

Passive noise control techniques are an effective way of mitigating environmental noise pollution caused by industrial activities, assisting with long-term sustainability in workplace health and safety. Excessive noise from various sources such as mining, construction, manufacturing, air blasting and large-scale gas and dust explosion investigations is challenging as it produces a high level of noise. Excessive explosion noise can have a significant impact on the surrounding environment and people. To suppress the noise to satisfactory levels for nearby occupants, several layers of acoustic barriers are employed. The effectiveness of each level of acoustic barrier is presented. A bottom ash granule base layer with a 300 mm thickness reduced the peak noise levels (136 dBA) by approximately 33 dBA. In the next stage, an autoclaved aerated concrete (AAC)-based 200 mm acoustic barrier was introduced, which suppressed 24 dBA of noise. The inside of the AAC acoustic barrier was finally covered with a 50 mm thick noise attenuation composite material layer constituted of a sound barrier and a sound absorber, and this composite material attenuated the noise level by 6 dBA. The entire noise suppression mechanism was found to be an effective way to suppress gas and dust explosion noise and satisfy the requirement of the occupant and sound level. Full article

This study focused on manufacturing efficient automobile sound-absorbing materials through alkaline treatment and dimple processing of recycled polyethylene terephthalate (rPET) nonwoven fabric. The rPET nonwoven fabric was produced with a sound-absorbing material through compression molding. It was improved through the development of porous sound-absorbing materials through alkaline treatment and resonant sound-absorbing materials through dimple processing. As a result of morphological analysis, alkaline treatment showed that pore size and air permeability increased according to temperature and concentration increase conditions. On the other hand, dimple processing caused a decrease in air permeability and a decrease in pores due to yarn fusion, and as the dimple diameter increased, the sound-absorbing coefficient increased in the 5000 Hz band. Finally, it was judged that effective sound absorption performance would be improved through a simple process through alkaline treatment and dimple processing, and thus there would be applicability in various industrial fields. Full article

In the last decade, various asphalt paving materials have undergone investigation for sound attenuation purposes. This research aims to delve into the innovative design of sustainable road pavements by examining sound absorption in rubber-modified asphalt mixtures. More specifically, the impact of alternative sustainable materials on the sound absorption of asphalt mixtures across different temperatures, precisely crumb rubber (CR) derived from recycling of end-of-life tires, was investigated. The acoustic coefficient and its Gaussian fit parameters (Peak, BandWidth, and Area Under the Curve) were evaluated. Five different types of asphalt mixtures were studied, encompassing dense, discontinuous, and open mixtures with 0%, 0.75%, and 1.50% CR incorporated through the dry process (DP). The results of sound absorption indicated a slight influence of crumb rubber at temperatures ranging from 10 °C to 60 °C, particularly in mixtures with high void content. On the other hand, as expected, the void content proved to be highly correlated with sound absorption. These findings facilitated the establishment of predictive models that correlate acoustic absorption spectra with the characteristics of asphalt mixtures. As a result, these models will be valuable in the design of the next generation of sound-absorbing pavements. Full article

The automotive industry needs to improve energy efficiency rapidly to achieve carbon neutrality while creating a safe, secure, and comfortable driving environment for customers. Porous sound-absorbing materials and porous thermal insulators are typically used to satisfy these requirements despite limitations in mass and space. While these porous materials are similar, the microstructures they offer for high performance differ in the size and connectivity of their fluid phases, which enhances the difficulty of achieving excellent sound absorption and thermal insulation in the same material. In this study, a hydrophobic cellulose nanofiber–poly(methylsiloxane) xerogel composite was developed using computational microstructure modeling. This porous material has high porosity and excellent thermal insulation and sound absorption properties. Full article

Noise pollution is a major threat to the health and well-being of the entire world; this issue forces researchers to find new sound absorption and insulating material. In this paper, the sound absorption coefficient and vibration damping factor of panels manufactured from Cyperus pangorei rottb and ramie fiber reinforced with epoxy resin are explored. Cyperus pangorei rottb grass fiber and ramie fiber are widely available natural fibers. Cyperus pangorei rottb grass fiber is used in mat manufacturing, whereas ramie is widely used as a fabric. Using both of these fibers, six variant panels using a vacuum resin infusion process (VRIP) were fabricated. The panels were named C, R, CR, RCR-Flat, RCR-Curved, and RCR-Perforated. All the panels were tested for the sound absorption coefficient using an impedance tube with a frequency ranging up to 6300 Hz. Modal analysis was carried out by using the impulse hammer excitation method. A micro X-ray computed tomography (CT) scan was used to study the voids present in the panels. The results were compared among the six variants. The results show that the RCR-curved panel had the highest sound-absorbing coefficient of 0.976 at a frequency range between 4500 Hz to 5000 Hz. These panels also showed better natural frequency and damping factors. The presence of internal voids in these panels enhances sound absorption properties. These panels can be used at higher frequencies. Full article

This study aims to tackle the challenge of high noise levels on balconies while preserving natural ventilation. Eight innovative balcony designs, incorporating elements like diffuser edges, undulating ceilings, Helmholtz resonators, grooves, or sound traps, were evaluated via finite element (FE) modeling. The insertion loss results showed that for many balcony designs, noise reduction in the balcony could deteriorate beyond an elevation of 8 m. However, the front jagged and full wavy ceiling designs were shown to be more robust in noise attenuation across balconies on different floors. The jagged ledge and grooved parapet designs yielded an overall 1.5 dBA lower SPL at the exterior regions, compared to other designs, which implies that the designs are less acoustically detrimental to nearby residential blocks as they tend to diffract and absorb incident noise. The jagged ledge design is more effective for lower floors while the jagged ceiling design is more effective for higher floors. A combination of the protruded jagged ledge for the lower floor and jagged balcony ceiling for the higher floor would result in the lowest noise ingress over three stories of residential units: this would be capable of achieving more than 3 dB noise reduction and would offer viable options for improving balcony noise mitigation, by providing valuable insights to architects and designers seeking practical solutions for outdoor noise reduction. Our study highlights that whereas the spectrum characteristics of acoustic absorption materials may be less tunable, and where reduced head space is traded for thicker material for greater ab-sorption and added affixation and maintenance cost, the jagged ledge and ceiling curvatures can actually be shape-tuned, say for every 3 to 4 floors up the high-rise to more effective reduce noise ingress and possibly improve the architecture façade outlook. Full article

Porous materials have emerged as one of the most widely employed sound-absorbing materials in practical applications, owing to their excellent sound absorption properties and lightweight nature. Unsaturated porous materials have the potential to achieve superior sound absorption effects and significantly reduce mass. However, current research on the sound absorption performance of unsaturated porous materials is limited. This paper used a modified transfer matrix method (MTMM), which relies on matrix dimensionality reduction, to analyze the sound absorption characteristics of unsaturated porous materials under various boundary conditions. The study also examines the impact of different parameters, such as material thickness and saturation, on sound absorption performance and compares the results. The findings indicate that when a solid elastic plate is attached to an unsaturated porous elastic plate, the absorption coefficient decreases while the transmission loss increases. Additionally, reducing the thickness of the plate and increasing its porosity and saturation levels lead to an increase in the absorption coefficient and a decrease in the transmission loss. Full article