Sound Absorption Layer Research Articles

Acoustic Performance of Porous Mortar and Potential Use for Traffic Noise Mitigation: A Review

Porous mortar (PM) is a porous building material used to reduce noise levels in economic emerging cities to achieve acoustic comfort. This research paper provides a comprehensive review of PM’s sound absorption performance as reported in selected published works. The selection criteria are limited to experiments conducted on specimens with a thickness ranging from 20 to 75 mm, a range suitable for application as a sound-absorbing layer on noise barriers or building walls. This paper explains the underlying principles of sound absorption in PM and outlining methods for assessing sound absorption. This review paper includes the performance of conventional or typical PM with modified PM, considering elements such as mix design and significant factors that influence sound absorption, notably material density, and pore size. Subsequently, this paper reveals on the evaluation of PM’s suitability as a sound-absorbing material, encompassing an assessment of its mechanical properties. In conclusion, the paper identifies the potential of PM as an efficient sound absorber, particularly in the context of mitigating traffic-generated noise.

Sound transmission loss of absorber-barrier-absorber structures with kapok fibers as absorption layers

The sound insulation of the front wall of a car is mainly used to isolate the noise of the engine from being transmitted to the passenger cabin. A front wall is generally a kind of structure of Absorber-Barrier-Absorber (ABA), where A is sound absorption layer and B is sound insulation layer. The sound absorption layer (A) usually consists of porous cotton of superfine fiber or microfiber. In this paper, kapok fiber is used to make the sound-absorbing layer A, and its sound absorption is compared with that of superfine fiber. Microstructure of the two fibers is compared, and it is found that kapok fiber has a large hollow structure. The sound absorbing coefficients of the layer A made with the two fibers are measured and it is concluded that the layer A made of kapok fibers can absorber noise greatly and thus has high sound absorption coefficient. The prototypes of ABA structural are made using two kinds of fibers as layer A, and the sound transmission loss (STL) was measured using reverberation room and anechoic room. The measurement shows that the ABA using kapok fiber as sound absorption layer has better sound insulations, and the STL of ABA using kapok fiber as sound absorption layer is increased by about 3 dB. A model for estimating STL of ABA structure is established and the calculated STL is validated. Using the developed model, the STL of ABA structures with different structural characteristics of Layers A or B is calculated and analyzed.

Experimental Analysis and Simulation of a Porous Absorbing Layer for Noise Barriers

Noise barriers are common noise mitigation measures usually implemented near roads or railways, with proven efficiency. This work presents a study of a porous concrete material incorporating expanded clay as aggregate, to be used on the sound-absorption layer of noise barriers. A theoretical material model is calibrated using experimental data and then used to estimate the diffuse field sound absorption from the normal incidence sound absorption estimation/measurement. Validation of such estimation is performed by comparing to reverberant room measurements. Numerical simulations are carried out using the boundary element method (BEM) and the CNOSSOS-EU calculation method to assess the performance of different types of barriers incorporating this material. L-shaped and vertical barriers are tested, as well as low-height and conventional (taller) barriers, employed in the context of a railway noise scenario. Different results are obtained by the two methods, mainly due to the different underlying physical principles. Good insertion loss values may be obtained using both conventional and low-height noise barriers together with the porous concrete material if a careful choice of its location within the barrier is made.

Investigation of the Underwater Absorption and Reflection Characteristics by Using a Double-Layer Composite Metamaterial

It is well-known that the acoustic stealth of an underwater vehicle composed of a non-watertight structure has been facing severe challenges. The origins of this effect are associated with the fact that the coupling between the water and the mechanical structure is not negligible because both sides are in the water. Along these lines, the idea of forward absorption and backward reflection was proposed in this work to address this issue. More specifically, a composite underwater acoustic metamaterial (AM) was designed based on different layers, namely a sound absorption layer and a sound insulation layer from the outside to the inside. The sound absorption layer was made of a soft rubber matrix with embedded steel scatterers (ESs) to enrich the coupled resonance effects, while the sound insulation layer was composed of hard rubber with a built-in cavity to improve the impedance mismatching between the AM and the water. The impact of the number and thickness of the embedded ESs on the acoustic performance of the AM was also thoroughly investigated via a finite element method (FEM). A fast non-dominated genetic algorithm (NAGA-II) with elite strategy was used to optimize the position and the size of the ESs. The optimization results revealed the high absorption at the forward incidence and the high reflection at the backward incidence. Thus, our work provides a novel and effective approach for improving the acoustic stealth of underwater vehicles composed of non-watertight structures.

Physical Properties and Environmental Impact of Sound Barrier Materials Based on Fly Ash Cenosphere

Traffic noise and solid waste pollution are two major problems that restrict urban development and affect urban environments. In this study, a new kind of cement-based material for sound barriers was prepared using industrial waste fly ash cenosphere to explore the material ratio of the sound absorption, sound insulation, and composite layers and to optimize the material’s properties. The research findings showed that the compressive strength had significant effects on the material properties of the sound absorption layer, with the optimal compressive strength range being 0.2–0.4 MPa. At 0.4 MPa, the material with an aggregate-to-binder ratio of 1.0 had the best comprehensive properties. The sound insulation layer had the best compressive strength of 29.00 MPa at a 45% fiber admixture. The composite had the best sound insulation when the thickness ratio of the sound absorption and insulation layers was 60:40, and the sound transmission loss was 38 dB. The embodied carbon (EC) and embodied energy (EE) of the new fly ash cenosphere across the whole life cycle were 57.57 kgCO2e and 477.08 MJ, respectively, which were 4.8−52.9% and 53.2−82.3% lower than other traditional sound barriers, respectively. Thus, they were environmentally friendly and had satisfactory energy-saving and environmental protection values.

Investigation of Acoustic Impedance of a New Floor Panel Filling Generation

Acoustic comfort is one of the main factors of a man’s comfortable existence in the residence places. Over the past century, a lot of experience has been accumulated in isolating rooms from noise using enclosing structures, but the acoustic regime is deteriorating due to the constant increase in the power and number of noise sources in localities and buildings themselves. Therefore, acoustic comfort is not always provided in the premises even with satisfactory sound insulation of enclosing, as experimental studies have shown. In addition, humanity strives to build structures with the lowest material and labor costs. All this makes us look for more effective solutions for sound insulation and sound absorption. A sound-proof panel made of acoustic resonators ZIPAR is a plate of sound-absorbing material consisting of an outer sealed, sound-absorbing and sound-insulating layers. The air cavities of the sound-absorbing layer are made of upper parts-resonators, in the form of truncated cones, which cross-section decreases in the direction of the outer layer, and the cavities in the sound-absorbing layer have a cylindrical shape; these are the lower parts-deflectors. The data obtained as a result of tests are intended for use as a reference material in the design and installation of noise protection premises, both in new construction and in the reconstruction and minor repairs of existing buildings.

On the issue of reducing the sound level emitted by the intake system of an internal combustion engine

There is currently a problem of acoustic contamination of environment caused by a large number of vehicles. One of the most intense sources of vehicle noise is its power plant - an internal combustion engine, including the exhaust system and the intake of the fuel-air mixture into the working cylinders. When studying the sound field emitted by the intake system of the engine, two components are distinguished: the gas-dynamic sound arising at the cut of the air intake pipe and the structural (body) sound resulting from sound reradiation by the vibrating walls of the body elements. The study of a technique for improving the acoustic characteristics of the engine intake system by making the sidewalls of the packaged component of the intake system in the form of a three-layer structure (mesh bobbin element - porous sound-absorbing layer - acoustically transparent gastight and watertight film) is examined in the article.

Sound absorption behaviors of metamaterials with periodic multi-resonator and voids in water

In this paper, a novel composite acoustic metamaterial comprising of periodic multi-resonator and voids is proposed, in which the periodic multi-resonator and periodic voids are embedded into the sound absorption layer and the sound insulation layer, respectively. The different arrangements for the two layers are designed, and the sound absorption behaviors of the proposed combinations immersed in water are researched using finite element method. In addition, the effects of different arrangements for the two layers, the multi-resonator in sound absorption layer and the void in sound insulation layer on sound absorption behavior of the combinations are also investigated. The numerical results show that the frequency band of sound absorption of the proposed combinations can be broadened effectively due to the coupled resonance generated by multi-resonator and voids. Moreover, the different arrangements for the two layers have significant impacts on sound absorption behaviors of the combinations. The results validate that the sound absorption in the low frequency band can be enhanced effectively by distributing sound absorption layer and sound insulation layer on both sides of steel plate.

Numerical optimization of sound pressure responses for the dash panel based on automatically matched layer and genetic algorithm

The sound insulation performance of the dash panel has a direct influence on the level of sound absorption of the whole vehicle. Therefore, it is necessary to adopt proper optimization strategies to optimize the dash panel and interior sound pressure response. Firstly, damping loss factor was imported into the dash panel and the coupling model of interior acoustic cavity to compute the sound pressure response of the driver. Sound pressure response had multiple peak noises in the analyzed frequency band. With the increase of the analyzed frequency, Contours for the noise of interior acoustic cavity became increasingly dispersed. Secondly, reverberation chambers on both sides were coupled with the dash panel respectively to establish AML model. In this way, the computational transmission loss would be more consistent with the actual situation. AML method can directly obtain transmission loss without extracting the transmission sound power to compute transmission loss through relevant formulas. In reported papers, there are big differences between simulation and experiment in the low frequency because it is difficult to simulate the real boundary conditions. The computational results of this paper were more consistent with experimental results in the whole frequency band, which indicated that it was more effective to use AML method to compute the transmission loss of the dash panel. Then, a sound package was applied to the dash panel to conduct parametric analysis. Results showed that the thickness of the sound-absorption layer could effectively improve transmission loss over 250 Hz. When the thickness of the sound-absorption layer was 15 mm, transmission loss was relatively optimal. In addition, the thickness of the air layer had little influence on transmission loss. Finally, genetic algorithm was also used to optimize the parameters of sound package of the dash panel. Results showed that the optimized dash panel had a higher average transmission loss and total mass, and the average sound pressure response of the driver also decreased. Additionally, the transmission loss and sound pressure response of the driver optimized by genetic algorithm at each frequency point were improved in the analyzed frequency band to obtain a low-noise and lightweight dash panel.

Improvement of sound insulation of doors or windows by absorption treatment inside the peripheral gaps

Slit-shaped gaps included in such building elements as doors and windows are apt to deteriorate sound insulation performance of the wall system. In order to reduce sound transmission through these parts, sound absorption layer is often put inside the gaps. In this study, the effect of such a sound absorption treatment was examined by numerical and experimental studies. In the numerical study, the effect of sound absorption treatment on the gaps existing around doors/windows was examined by applying the FDTD method. To examine the results of the numerical study, a full-scale model experiment was performed using the sound intensity measurement method. A considerably good agreement was found between the results of the numerical study and those of the experimental study. As a result, it has been indicated that the sound insulation defect caused by the sound transmission through the gaps can be much improved by sound absorption treatment inside the gaps. Narrow gaps which exist around the door panel or window sash are apt to deteriorate sound insulation performance of the total wall system. The influence of the acoustical transmission through the gaps or apertures has been theoretically investigated [1-6]. More practical case studies on sound insulation performance of such real building elements with gaps as doors and windows has also been investigated [7-11]. However, prevention of sound transmission through such peripheral gaps has not been reported. In this study, therefore, we examined the effect of sound absorption treatment in narrow gaps with various shapes in cross section. As a case study, in-situ measurement of sound insulation performance of a door panel in an office building was performed under the conditions of with and without absorption treatment.

현장실험을 통한 목조바닥의 구성요소가 충격음 차단성능에 미치는 영향 평가

바닥구조의 충격음 차단성능은 바닥의 구성요소에 의해 많은 영향을 받는데, 그중 목조 바닥구조의 경우 중량의 흡읍층과 바닥구조의 강성이 주요한 영향인자로 고려되어 왔다. 본 연구에서는 국내 시공된 목조 건축물에 대해서 현장 실험을 통해 바닥 구성요소가 충격음 차단성능에 미치는 영향에 대해서 살펴보았다. 목조 바닥의 충격음 차단성능은 상대적으로 낮은 저주파수 대역에서의 음압레벨에 의해 전체적인 성능이 좌우되었으며, 흡읍층과 바닥구조의 강성 보강에 의해 저주파수 대역 음압레벨을 감소시켜 충격음 차단성능을 향상시킴을 알 수 있었다. 특히, 바닥난방을 위해 설치되는 시멘트 몰탈층과 같은 충격음 흡수층과 원래 경간의 중간 지점에 보를 설치하여 장선 경간을 줄여줌으로써 목조 바닥의 강성을 증가시킨 경우에 중량 충격음 차단성능이 크게 향상되었다. Constituents of timber framed floor affect the insulation performance against impact sound significantly. Among them, installation of massive sound absorbing layer and reinforcement of stiffness of timber floor have been considered as major factors that improve the insulation performance against impact sound. Researches on evaluating the effect of floor constitutions have been carried out through the field measurements for timber framed buildings in Korea. It is concluded that the impact sound pressure level at the relatively lower frequency governs the overall insulation performance, and can be improved by the installation of sound absorbing layer and reinforcement of floor stiffness. Especially, the insulation performance against heavy impact sound was improved significantly when the massive cement mortar layer for floor heating system was installed and the stiffness was reinforced by shortening the joist span using additional beam at the mid-position of original span.

GARMENT WITH SPEAKER FUNCTION

A garment with a speaker function is provided. The garment includes a garment body, a bag, and an electret speaker. The bag disposed on the garment body includes a sound-absorbing layer. The electret speaker, disposed in the bag, gives off sounds to a first direction and a second direction at the same time. The sound-absorbing layer absorbs the sound of the second direction. Therefore, the present invention not only provides convenience to the user, but also enhances the acoustic quality of the electret speaker.

Effect of absorption layer on interior sound field of sonar dome

Using the finite element method (FEM) and boundary element method (BEM) and considering the sound absorption layer which is covered on the backing of the sonar dome, the interior field in the dome which is excited by the incident plane wave has been studied. This method is validated by comparing numerical results with that of classic elastic theory. Then the effect of parameters of the sound absorption layer on interior sound field has been analyzed. The numerical calculation results show that uniformity of interior sound pressure is improved when the backing is covered with a sound absorption layer. The thicker the layer is, or the higher the loss factor of layer is, the more uniform the sound field is.

Tunable sound absorbing and air filtering attenuating device

Acoustical attenuating devices (52) and method of forming them. The attenuating devices (52) include an exterior layer (64), a sound absorption layer (66), and multiple perforated layers (68) coupled to the sound absorption layer (66). The perforated layers (68) include a perforated structural layer (70) and a perforated substrate layer (72). The perforated structural layer (70) and the perforated substrate layer (72) provide structural stiffness and define multiple resonating tubes (88) that attenuate sound.

Sound absorbing/sound blocking automotive trim products

Sound absorbing/sound blocking products, including trim products formed from a porous fibrous layer backed by a sound absorbing layer and a sound blocking layer for use within vehicles, and methods of making same, are provided. A porous fibrous layer structure including a fibrous layer backing is heated to achieve a fluid or semi-fluid state and then subjected to vacuum to draw air through the fibrous layer backing to create a porous structure. A layer of sound absorbing and a layer of sound blocking material may be applied to the porous fibrous layer backing to provide improved acoustic properties. An underlayment may further be included to provide selected areas of increased thickness and provide tailoring of sound attenuation.

Lightweight speaker enclosure

A speaker enclosure having a substantially seamless rigid outer skin, a middle sound absorbing layer, and a substantially seamless inner skin results in a lightweight speaker having sound absorbing characteristics. The speaker enclosure is comprised of two basic parts, a box section and a baffle section where each of these sections include a rigid outer skin, the middle sound absorbing layer and a seamless inner skin and are made according to the same method. The outer skin is formed from a layer of sheet molding compound, the middle sound absorbing layer includes pieces of honeycomb material, and the inner skin is formed from a layer of sheet molding compound. The layers of material are placed into a mold and then cured through vacuum bagging and heating thereby producing a strong, lightweight speaker enclosure made of materials which attenuate the transmission and retransmission of errant sound waves in the enclosure thereby reducing distortion of the sound signal produced by the speaker.

Ceiling element for a composite ceiling

The invention relates to a ceiling element (1) for a ceiling (D) consisting of several ceiling elements, comprising a lower metal support (4) which is divided up by links (7) and has holes; and an active sound layer (5) which is arranged in the metal support. Said layer is a sound insulation layer or a sound absorption layer for example, especially in the form of an open-pore foam such as a melamine-resin foam. The active sound layer (5) is bonded to the metal support (4). According to the invention, the adhesive (6) is only applied to the link areas (11) and only the inner surfaces of the link areas (11) are bonded. This guarantees a simple, economical construction.

Noise Reduction in Units for Pneumatic Weaving of Complex Fibres

A method of designing the soundproofing jacket for mechanisms for pneumatic weaving of complex fibres as a nonhermetic screen with process openings is confirmed by the results of experimental studies. The design of the soundproofing jacket with a coating of VD-17-58 vibration-damping mastic allowed reducing the sound pressure level by 14-15 dB (sound level by 5-6 dBA). The sound-absorbing layer of synthetic carpet decreases the noise by an additional 8-10 dB, and incorporation of additional polyurethane foam sound absorbers allowed reducing the noise level to the health standards.

Monitoring air–sea exchange using ambient sound

Wave breaking and precipitation are important processes contributing to the exchange of momentum, heat, water, and gas at the air–sea interface. These processes are also principal generators of high-frequency (over 1 kHz) underwater ambient sound. Furthermore, the bubbles generated by the breaking waves and raindrop splashes can be stirred downward into the ocean mixed layer forming an effective sound absorption layer. When present this layer modifies the ambient sound field, and can thus be detected using passive acoustics. Using the passive sound field as the exploratory tool, more conventional measurements of salinity, temperature, bubbles, wind, and surface waves will be examined. Anomalies in near-surface salinity are explained by acoustically derived rainfall and wind-speed measurements. Acoustically derived rainfall measurements suggest that rain affects the surface wave field. Enhanced injection of bubbles into the mixed layer by rain in the presence of high wind is indicated by changes to the shape of the underwater sound spectrum. [Work supported by ONR Ocean Acoustics and NSF.]

Method and apparatus for acoustical partition

A new and improved method and apparatus for an acoustical partition are presented. The acoustical partition comprises a wall section defining an enclosed space, a frame structure contained within the wall section, and an insulation layer contained within the frame structure such that an air cavity is created at the centermost area within the wall section. The acoustical partition may also include a sound absorption layer placed on a front side of the wall section, and a fabric layer positioned over the sound absorption layer in such a way as to provide an airspace between the sound absorption layer and the fabric layer.