Sound Absorption Levels Research Articles

The potential of flip-flops waste as an environmentally friendly sound-absorbing material

Abstract Rubber flip-flops waste is a type of waste that is difficult to decompose, it needs to be recycled into useful items to reduce the negative impact on the environment. This research aims to test the sound absorption coefficient of waste flip-flops as a basic material for making environmentally friendly acoustic panels. The method used is simulation and modeling, making samples by mixing flip-flops rubber particles and the binding material as neoprene glue. Tests were carried out on two samples of acoustic panels with particles measuring 3 mm and 7 mm using animpedance tube. The research results show that panels with a particle size of 7mm can achieve a higher level of sound absorption in the frequency range of 200 Hz - 1600 Hz compared to particles measuring 3 mm. The conclusion is that used flip-flops have the potential to become acoustic panels that can absorb sound. This research offers an environmentally friendly solution for managing flip-flop waste and processing it as an acoustic panel product that effectively reduces disturbances.

SCIENTIFIC APPROACHES TO THE DEVELOPMENT OF COMPOSITES MATERIALS FOR REDUCING VIBRATION AND NOISE IN PRODUCTION

Goal. Scientific approaches to the development of composite materials for noise and vibration reduction in the workplace and evaluation of their effectiveness. Methodology. Сomplex of scientific methods for assessing the impact of environmental factors, such as noise and vibration, on the worker was used for the research. Сomparative evaluation of the effectiveness of the developed composite materials with the existing ones was carried out in terms of their ability to reduce noise and vibration at the worker's workplace. Results. New composite materials with an extended spectrum of action have been developed. Their effectiveness in laboratory and production conditions was evaluated. Their effectiveness was evaluated at those workplaces where an increased level of noise and vibration is registered, a comparative analysis of the new vibration-absorbing materials developed by the authors with those existing in laboratory and production conditions was carried out.Conducted studies have shown that «Vibroshtil» and «Vibroshtilmaxi» vibration-absorbing materials are characterized by a higher level of sound absorption compared to both domestic and materials of the same purpose produced in other countries, and are proposed for implementation in production, railway transport and the subway. Conducted studies have shown that «Vibroshtil» and «Vibroshtilmaxi» vibration-absorbing materials are characterized by the higher level of sound absorption compared to both domestic and materials of the same purpose produced in other countries, and are proposed for implementation in production, railway transport and the subway. The comparative evaluation made it possible to prove the effectiveness of the developed composite vibration-absorbing materials for the correction and reduction of noise and vibration levels in workplaces. The results were achieved due to the optimal selection of ingredients of composite materials and their ratio. Scientific novelty. The effectiveness of new composite materials «Vibrostil» and «Vibrostilmax» for reducing noise and vibration levels at workplaces was developed and evaluated, and their effectiveness was evaluated in order to prevent the risk of workers suffering from vibration sickness. Practical significance. The introduction of developed vibration-absorbing materials will reduce the level of noise and vibration in the workplace and reduce the risk of workers suffering from vibration sickness.

ANALISIS TINGKAT REDAM BUNYI DARI BEBERAPA JENIS BAHAN AKUSTIK KAIN PERCA

Research was carried out on the analysis of the sound absorption level of several types of patchwork acoustic materials which aims to find out whether patchwork can be used as a sound dampening material, to determine the sound absorption level of several types of patchwork acoustic materials and to determine the best attenuation level of several types of patchwork acoustic materials. the type of patchwork acoustic material. The background of this research is due to the acoustic quality of the room which has received less attention for the comfort of listeners when they are in a room. The study used variations of sound absorbing materials, namely cotton and denim patchwork. Measurement of the sound absorption coefficient of patchwork is done by making a sample chamber with a length of 13.5 cm, a width of 13.5 cm and a height of 8.5 cm. Sound Level Meter is a tool used to measure the level of sound pressure. Variations in the thickness of the patchwork used were 3, 5, and 10 mm. In measuring the entire inner wall surface of the sample room will be covered with patchwork, then the speaker is placed in the sample room. The sound source comes from speakers with a frequency of 90 dB which is arranged in a frequency range of 125, 250, 500, 1000, 2000 and 4000 Hz. The best damping level of the three materials is a mixture of cotton and denim with a thickness of 10 mm, because the thicker the patchwork layer, the α value obtained is 0.629.

A tunable slit-plate absorber with multiparameter cooperative control

Tunable acoustic metamaterials have a more flexible operating spectrum while still controlling acoustic waves via subwavelength thickness, but their operating range and acoustic absorption performance are limited by a single-parameter tuning mechanism. In this study, we first propose a slit-plate absorber with reconstructed porosity, which has a dynamic continuous tuning capability and is easier to achieve low-frequency resonance. Then, in order to improve its acoustic absorption performance, we study the tuning laws of numerous structural factors as well as their cooperative interaction. Local parameter changes to achieve impedance compensation and isotropic control to enhance frequency shift are presented to greatly improve the tunable range and sound absorption level. A tunable absorber with multi-parameter cooperative control is constructed using this method. The results reveal that continuous tuning of 210–920 Hz is possible at a total thickness of 25 mm, and the sound absorption coefficient in the tuning range is more than 0.8, and the thickness of the structure at 210 Hz is 1/65 of the absorption wavelength. Our work demonstrates a new method for improving the performance of adjustable acoustic metamaterials and promotes the use of acoustic metamaterials in low frequency changing noise environments.

Development of ultra-broadband sound absorber based on double-layered irregular honeycomb microperforated panel

In this study, a broadband sound absorber was developed using a double-layered irregular honeycomb microperforated panel (MPP) structure and a particle swarm optimization (PSO) algorithm to address the issue of broadband sound absorption of MPPs. An acoustic impedance model of the designed sound absorber and an optimization algorithm were implemented to obtain the structural configuration parameters for quasi-perfect sound absorption. The coupling effect between the resonant elements and the optimized structural configuration parameters enabled broadband and high-efficiency sound absorption. The impedance tube experimental results demonstrated an excellent broadband sound absorption level within the range of linear acoustics, and the designed triad and tetrad structures exhibited more than 70% absorption efficiency in the range of 609–4 002 Hz and 518–5 162 Hz, respectively. This study provides a design method and insights into the design, promotion, and application of broadband sound absorbers.

The Application of Nanofibrous Resonant Membranes for Room Acoustics

Solitary sound absorbing elements exist; however, their construction is massive and heavy, which largely limits their use. These elements are generally made of porous materials that serve to reduce the amplitude of the reflected sound waves. Materials based on the resonance principle (oscillating membranes, plates, and Helmholtz's resonators) can also be used for sound absorption. A limitation of these elements is the absorption of a very narrow sound band to which these elements are "tuned". For other frequencies, the absorption is very low. The aim of the solution is to achieve a high sound absorption efficiency at a very low weight. A nanofibrous membrane was used to create high sound absorption in synergy with special grids working as a cavity resonator. Prototypes of the nanofibrous resonant membrane on a grid with a thickness of 2 mm and an air gap of 50 mm already showed a high level of sound absorption (0.6-0.8) at a frequency of 300 Hz, which is a very unique result. Since acoustic elements, i.e., lighting, tiles, and ceilings, are designed for interiors, an essential part of the research is also the achievement of the lighting function and the emphasis on aesthetic design.

Design and study of broadband sound absorbers with partition based on micro-perforated panel and Helmholtz resonator

Micro-perforated panel (MPP) absorber has various merits, so it has great potential for application in the field of noise control. In this paper, the cavity with a variable section partition was designed to solve the broadband sound absorption problem of MPP. Three types of sound absorbers were developed with subwavelength thickness based on the cavity: Micro-perforated panel with built-in Helmholtz resonator (MPPHR), single-layer and double-layer micro-perforated panel backed by the cavity (SL-VMPP and DL-VMPP, collectively referred to as VMPP). The absorption characteristics of three sound absorbers with various partition parameters were investigated by COMSOL Multiphysics software. Furthermore, three types of absorbers were optimized with particle swarm optimization (PSO) algorithm for a superior absorption performance. Finally, the experimental results demonstrate predicted improvements in broadband sound absorption levels when compared to conventional MPP absorber: The MPPHR with a thickness of 32 mm (∼λ/18 at the first resonant frequency) has a half absorption band of up to 1294 Hz, which is nearly 500 Hz wider than the conventional MPP with equal cavity depth. The optimized SL-VMPP and DL-VMPP have an absorption level of at least 80 % in the frequency range of 794–1614 Hz and 632–1954 Hz, respectively.

ПОЛНОСТЬЮ РЕЦИКЛИРУЕМЫЕ ЗВУКОПОГЛОЩАЮЩИЕ ПАНЕЛИ ДЛЯ ШУМОЗАЩИТНЫХ ЭКРАНОВ

There are thousands of kilometers of noise protection screens around the world along roads, railways and near airports. The use of such screens poses some issues. Barriers often lack the required level of sound absorption and have low durability. Screens can be noise-absorbing, noise-reflecting or both. Sound absorbing materials are used to suppress noise at medium and high frequencies. For sound deadening at low frequencies, resonant absorbers are used; they are Helmholtz resonators combined into a single structure. When panels reach the end of their life cycle, they must be recycled. Separating wood, metal, fiberglass or rock wool slabs wrapped in fiberglass is not easy. The production of mineral fiber requires a lot of energy. A selection of materials has been proposed and the properties of fine-grained concretes for the further manufacture of a noise-protective panel have been investigated. The perforated front and blank rear walls are made of fine-grained basalt fiber-reinforced concrete reinforced with alkali-resistant basalt fibers. The results of studies of fine-grained basalt concrete confirmed the effectiveness of the combined use of basalt fibers and superplasticizer Master Glenium 115. The physical and mechanical characteristics of basalt fiber-reinforced concrete are increased by about 70–80 % compared to traditional concrete, which will further increase the durability of imitation noise protection panels.

Development and Evaluation of Acoustic Sound Absorption Composite from Orange Peels Residues and Sachet Water Bags

The goal of this study was produce a device that would reduce the unwanted sound/noise produced by machines encountered in our daily activities using orange peels (agricultural residues) and sachet water bags. These materials were prepared, mixed in 70:30 % ratio and transferred into a two-roll mill (compounding machine), where they were melted at about 150oC temperature before transferring them to a compressing machine that was set at a lower temperature of 130oC. The composite panel was coupled together to form a box where three speakers were connected to MP3 and inserted into the box. Test was carried out to check for the sound absorption levels of the composite using a sound level meter. Results obtained show that ‘A’ weighing filter covers the full frequency range of 0–90 kHz before coupling the absorption box. This could irreversibly damage the auditory system since it fell outside the acceptable range of 0–80 dB frequency sensitivity of human ear. However, the sound level becomes within the acceptable frequency when coupled to the developed absorption box indicating that the composite board using orange peels and empty water sachet is a good sound absorber.

A broadband sound absorber of hybrid-arranged perforated panels with perforated partitions

Several parts of panels with different perforated characteristics and cavity depths are integrated to present a novel hybrid-arranged perforated panel with perforated partitions. Perforated panels in the same layer are divided by perforated partitions. By designing the parameters of the perforated panels and the depths of the air cavities, the sound absorption coefficient (SAC) of the structure can be greatly enhanced. The equivalent circuit method (ECM) is applied to analyze the acoustic impedance of the structure. An acoustic experiment and numerical simulations by the finite element method are carried out to validate the results of the proposed analytical model. From the investigations, it is found that the SAC of the model has not only a wideband but also a high sound absorption level. The hybrid-arranged perforated panel with perforated partitions provides a new way to design sound absorbers for practical applications.

Slanted septum and multiple folded cavity liners for broadband sound absorption

The design of acoustic liners with complex cavities for a wide frequency range of attenuation using numerical method is investigated in this paper. Three novel liner concepts are presented, demonstrating predicted improvements in broadband sound absorption when compared with that for conventional designs. The liners include a slanted septum core, a slanted septum core with varying percentage open area, and a MultiFOCAL concept. A finite element model of a normal incidence impedance tube is developed using COMSOL Multiphysics modeling software to predict the acoustic properties (resistance and reactance) of liners at medium and high sound pressure levels, and to study the impact of variations in the liner design parameters. The impedance tube finite element model incorporates non-linear semi-empirical impedance equations, validated by comparing numerical results with measurements performed on a single-degree-of-freedom liner, with a perforated face sheet, at high sound pressure level. The design variables of the novel liner concepts are optimized using a hybrid automated optimisation procedure. The low-frequency optimum slanted septum core concept with an open area of 4.5% for the face sheet and 18% for the short slanted septum is predicted to have an absorption level of at least 14 dB in the frequency range of 400–1000 Hz for normally incident pure tone excitations at 150 dB. The slanted septum core concept with varying percentage open area, with broadband optimum design variables, is predicted to have good broadband sound absorption levels of at least 10 dB in the frequency range of 570–3800 Hz. Finally, the MultiFOCAL liner concept with optimised percentage open areas is predicted to have an excellent broadband sound absorption levels of at least 14 dB, for pure tone excitations at 150 dB, in the frequency range of 900–5300 Hz. This work will be followed by optimisation of the face sheet geometries of these novel liner designs in order to maximise lined duct attenuation for aircraft engine applications.

Lightweight concrete for frame-monolithic construction

The proposed article is devoted to the study of the properties (strength, impact strength, sound absorption) of lightweight concrete used for frame-monolithic construction. Characterized by the well-known advantages (reduced load on the foundation, reduced consumption of reinforcement, as well as improved heat and sound isolation), lightweight concrete requires additional technological methods to achieve the necessary mechanical characteristics - compressive strength and impact strength. An alternative to the traditional preparation of concrete mixtures is proposed a technology using a high-speed mixer-activator in the presence of ground chamot, superplasticizer C-3 with the introduction of hydrophobic expanded clay gravel up to 75% of the amount of granite crushed stone. The use of mechanical activation leads to an increase in impact strength by 44% compared to the control, and makes it possible to obtain concretes, the sound isolation level of which provides the maximum efficiency of impact noise isolation and is equal to 45.7 - 42.8 dB in three frequencies, and the sound absorption level is 39. 8 - 49.7 dB.

A self-consistent approach for the acoustical modeling of vegetal wools

Vegetal wools have the capacity to store atmospheric carbon dioxyde, one of the main gases responsible for climate change. So, these insulating materials are used as key elements for green buildings. Moreover, vegetal wools present high sound absorption level performances contributing to the acoustic comfort of indoor living spaces. These properties are directly related to the morphology and the size of their vegetal fibres. Thus, to take their microstructural specificities into account for the modeling of their sound absorption properties, a micro-macro homogenization approach based on a cylindrical geometry is developed. This modeling method, based on a mix between Homogenization of Periodic Media (HPM) and Self-Consistent Method (SCM), is called SCMcyl. The macroscopic behaviour laws of materials are rigorously obtained by using HPM. Then, the SCM leads to the establishment of two possible analytical solutions (a velocity approach v and a pressure approach p) under the fundamental assumption of the energy equivalence between a generic cylindrical inclusion, representative of the vegetal wools physical and geometrical properties at microscopic scale, and the homogeneous equivalent medium at the macroscopic scale. The two modeling approaches developed in this paper, SCMcyl−v and SCMcyl−p, can be used to determine the sound absorption of fibrous materials using only two parameters, an equivalent fibre radius value and the material porosity. Finally, these solutions are validated for the vegetal wools case by comparison with experimental measurements.

Sound-Absorbing Polymer Composite Materials for Construction Purposes

The paper presents the results of a study of the influence of the nature fillers (wood flour, wood dust, vermiculite, expanded vermiculite, organoclay) and a polymer matrix (elastomer and thermoplastic) on the sound-absorbing and physico-mechanical characteristics of polymer composite materials. As a result of the studies, it was shown that sound absorption depends on the polymer matrix used - the sound absorption coefficient in the frequency range 2500-5000 Hz is greater for an elastomer-based composite material. It was also found that the nature of the studied fillers, as well as their content, practically does not affect the level of sound absorption of the polymer composite material. Differences appear only at a frequency of 6300 Hz. At high frequencies, expanded vermiculite has shown itself to be the most effective filler in terms of improving sound insulation properties. In the case of using, as a polymer-based thermoplastic, the introduction of a filler does not affect the values of the sound absorption coefficient in the entire frequency range.

Broadening sound absorption coefficient with hybrid resonances

In the last years, a great research effort has been focused on the noise mitigation at low frequencies. Membrane-type acoustic metamaterials (AMM) are one of the most promising solutions to meet the growing demand for low frequency sound absorbers. Typically, acoustic membrane absorbers require large back cavities to achieve low frequency sound absorption, which is usually categorised by a single narrow absorption peak. This paper presents an acoustic resonator unit cell, comprising of a thin elastic silicone plate with an air gap cavity with broadband absorption in a frequency range between 250 and 400 Hz. The broadband and multiple peak sound absorption showed by the proposed resonator is due to hybrid resonances which occur in the frequency range due to coupling of the structural dynamic response of the plate with the acoustic response of the air cavity. A numerical model based on acoustic-structural interaction, validated for experimental data, has been used to explain how the broadening gain in the sound absorption level is strictly related to the hybrid resonances of the unit cell resonator. We demonstrated that hybrid resonances are a function of the geometrical parameters and the ratio between the Young’s modulus and the density of the material plate, thus the proposed resonators absorption frequency range is tuneable at low frequencies allowing a wider broadband not achievable with acoustic membrane absorbers.

Reduction of Noise in The Vehicle Cabin by Using Natural Fibres with Polyurethane and Comparison with Other acoustic Materials

As natural fibres are noise-absorbing materials, biodegradable and renewable by using natural fibres such as betel nut, sugarcane fibres are combing with polyurethane for the automobile application to reduce cabinet noise of the vehicle, which currently contains traditional materials such as foams, glass, metals and plastics that are difficult to recycle. Four samples of natural fibres were prepared with different quantities of betel nut & sugarcane ratios of 35: 35, 50: 20, 55: 15, 60: 10. Polyurethane is common with 30% of all samples. The sound absorption coefficient (SAC) in the material was tested by using impedance tube and compared with other acoustic material like nitrile rubber, nonwoven polyester fabric and glass wool. It was observed that betel nut & sugarcane showing better SAC than other acoustic materials mainly at lower and higher frequency 60% betel, 10% sugarcane & 30% polyurethane showing better sound absorption level.

Effective sound-absorbing material for transport technological machines of railway transport

The article discusses the types and features of the operation of transport technological machines of the railways of the Russian Federation on the example of the most frequently used track machines, and presents methods for noise reducing on the railways of the Russian Federation. The most effective method to reduce the noise arising during the operation of track machines is identified - this is the installation of a steel soundproofing hood (casing) over the electric motor. The calculation of the effectiveness of sound-absorbing materials used for cladding steel bonnet is given. According to the results of the calculation, the material «asbestos felt» turned out to be the most effective, but the other materials under consideration, and in particular, «glass wool», «mineral wool» and «construction felt», turned out to be also applicable to the lining of the steel bonnet, since the calculations revealed the applicable level of sound absorption, which is less than a decibel in terms of noise reduction to the material «asbestos felt».

Modelling of a thermally activated building system (TABS) combined with free-hanging acoustic ceiling units using computational fluid dynamics (CFD)

Thermally Activated Building Systems (TABS) have proven to be an energy-efficient solution to achieve optimal indoor thermal environment in buildings. This solution uses the building mass to store heat and by means of water pipes embedded in the concrete slabs adjust the temperature in the premises. The active surfaces of TABS need to be as exposed as possible, but exposing bare concrete surfaces has a negative impact on the acoustic quality in the premises. Acoustic solutions capable of providing optimal acoustic comfort while allowing the heat exchange between the TABS and the room are desirable. This study focuses on the influence of two types of free-hanging ceiling absorbers (horizontal and vertical) on the cooling performance of the TABS. Different scenarios are investigated for each type of sound absorber. Computational Fluid Dynamics (CFD) simulations are used to illuminate the nature of the heat exchange between the TABS and the room and the occupants. The simulations are validated by comparison with full scale measurements in laboratory conditions. The study shows that for equivalent sound absorption levels, free-hanging vertical sound absorbers have a lower impact on the heat exchange between the room and the TABS compared to free-hanging horizontal sound absorbers. Cold air stagnation between the sound absorber units and the TABS has been identified as the major cause of the cooling performance decrease of the TABS.

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.

Development of Effective Textile-Reinforced Concrete Noise Barrier

Thin-walled, high-strength concrete elements exhibiting low system weight and great slenderness can be created with a large degree of lightweight structure using the textile-reinforced, load-bearing concrete (TRC) slab and a shell with a very high level of sound absorption. This was developed with the objective of lowering system weight, and then implemented operationally in construction. Arising from the specifications placed on the load-bearing concrete slab, the following took place: an adapted fine-grain concrete matrix was assembled, a carbon warp-knit fabric was modified and integrated into the fine concrete matrix, a formwork system at prototype scale was designed enabling noise barriers to be produced with an application-oriented approach and examined in practically investigations within the context of the project. This meant that a substantial lowering of the load-bearing concrete slab’s system weight was possible, which led to a decrease in transport and assembly costs.