Sound Insertion Loss Research Articles

Validation of Noise Barrier Insertion Loss Simulation in Reducing Road Traffic Noise by Site Measurement Data

A noise barrier serves as a method to control noise pollution resulting from road traffic, particularly prevalent in rural areas near heavy traffic routes such as highways. This study focuses on simulating the sound Insertion Loss (IL) of existing noise barriers designed to mitigate road traffic noise around school areas. The primary goal is to assess the precision of the Finite Element Modeling (FEM) program. Utilizing the finite element analysis software, COMSOL, the study models the noise barrier and its surroundings in two-dimensional acoustic radiation problem based on on-site dimensions and parameters. By examining the often-neglected aspect of noise leakage and its impact on noise reduction, the research aims to provide specific guidance for urban planners and architects to optimize noise mitigation in various urban settings. The study reveals a strong agreement between the simulated IL and on-site measurements, with a minimal difference ranging from 0.4 dB to 1.1 dBA on average. Additionally, the research suggests potential improvements to simulation accuracy through adjustments in aperture sizes. The findings demonstrate that finite element simulation can be a valuable tool for designers to assess the effectiveness of noise barriers before construction begins.

Reconfigurable 3D printed acoustic metamaterial chamber for sound insulation

In this study, we propose a new reconfigurable hexagonal-shaped Helmholtz resonator with a slit in each side. Numerical and experimental investigation of a single unit cell and the whole acoustic metamaterial chamber highlights the reliability and feasibility of the proposed metastructure. Highly efficient sound insertion loss can be captured with a simple and easily accessed resonator. By carefully designing rotation support in each unit cell and manufacturing a 3D printed base with periodic holes, the assembled resonators can be easily rotated, and the finite acoustic metamaterial chamber can be tuned to another configuration without the need of reprinting and redesigning the whole structure. The mechanisms of the proposed system are systematically explained by numerical computation (2- and 3-dimensions), band structure analysis, insertion loss and the corresponding experimental measurements. Specifically, the flat bands in the band structure reveal the weak coupling between the neighbouring resonators, and the highly trapped acoustic energy indicates that the bandgap originates from the local resonance mechanism. Thus, even one single unit in the system can efficiently attenuate the noise at mid frequencies, and the effects become better when the number of resonators increases. These phenomena can also be explained by the sound pressure map in the waveguide analysis and the characteristics of the insertion loss. Interestingly, by changing the configuration of the full chamber, the device can keep the insertion loss at a high level, while exhibiting a better ventilation ability. Therefore, with the high degree of freedom of tuning, it is possible to actively control the whole system to simultaneously achieve efficient noise cancelling and free airflow. The reconfigurable, scalable, feasible and controllable system can be easily applied to several practical scenarios like the silent zone in the city center, the ventilated noise isolate device for the machines, and optically transparent ventilation sound-insulating structures.

A multi-physics approach for modelling noise mitigation using an air-bubble curtain in impact pile driving

Underwater noise from offshore pile driving has raised significant concerns over its ecological impact on marine life. To protect the marine environment and maintain the sustainable development of wind energy, strict governmental regulations are imposed. Assessment and mitigation of underwater noise are usually required to ensure that sound levels stay within the noise thresholds. The air-bubble curtain system is one of the most widely applied noise mitigation techniques. This paper presents a multi-physics approach for modeling an air-bubble curtain system in application to offshore pile driving. The complete model consists of four modules: (i) a compressible flow model to account for the transport of compressed air from the offshore vessel to the perforated hose located in the seabed; (ii) a hydrodynamic model for capturing the characteristics of bubble clouds in varying development phases through depth; (iii) an acoustic model for predicting the sound insertion loss of the air-bubble curtain; and (iv) a vibroacoustic model for the prediction of underwater noise from pile driving which is coupled to the acoustic model in (iii) through a boundary integral formulation. The waterborne and soilborne noise transmission paths are examined separately, allowing us to explore the amount of energy channeled through the seabed and through the bubble curtain in the water column. A parametric study is performed to examine the optimal configuration of the double bubble curtain system for various soil conditions and pile configurations. Model predictions are compared with measured data. The model allows for a large number of simulations to examine different configurations of a single bubble curtain and a double big bubble curtain.

Reconfigurable acoustic metamaterial chamber for low-frequency noise mitigation

In this study, a new reconfigurable sonic crystal metamaterial chamber is proposed for noise mitigation. Each element of the sonic crystal is made on non-circular cross-section with built-in Helmholtz resonators. Numerical and experimental investigation of a single unit cell and the whole acoustic metamaterial chamber highlights the reliability and feasibility of the proposed sonic-crystal based meta-structure. Highly efficient sound insertion loss can be captured with a simple and easily accessed resonator. By carefully designing rotation support in each unit cell and manufacturing a 3-D printed base with periodic holes, the assembled resonators can be easily rotated, and the finite acoustic metamaterial chamber can be tuned to another configuration without the need of reprinting and redesigning the whole structure. By changing the configuration of the full chamber, the device can keep the insertion loss at a high level, while exhibiting a better ventilation ability. The reconfigurable, scalable, feasible, and controllable system can be easily applied to several practical scenarios like the silent zone in the city center, the ventilated noise isolate device for the machines, and the fully optically transparent ventilation sound-insulating structures.

Sound Insertion Loss Performance of Baffles with Devulcanized Waste Rubber

In this study, the insertion loss of devulcanized waste rubber baffles was evaluated. Acoustic baffles are suitable for reducing noise from the devices or machines by interfering with their emitting sound waves. Knowledge of the acoustic properties of the material used is of significant importance in ensuring the effectiveness of the acoustic properties of the baffle. Basic properties include airborne sound insulation, which is usually determined during laboratory testing. Baffle consists of sound absorbing and sound insulating materials. In this study, plasterboards were used as sound insulating material and devulcanized waste rubber as sound absorbing material. Devulcanization targets mostly the scission of sulphur crosslinks. Devulcanization techniques that have been explored in rubber recycling include thermos-chemical, microbiological, ultrasonic microwave thermos-chemical devulcanization in a supercritical carbon dioxide medium (scCO2). In this study, two types of rubber granules were devulcanized by grinding method and one other type was chemically devulcanized. Three types of rubber granules were mixed together in increasing 25 % proportion steps and glued with patented polyurethane glue. Total of 15 different composition devulcanized waste rubber granule boards were made. Rubber boards were attached together with the plasterboards. Insertion loss of the different composite baffles was measured in semi-anechoic chamber in a purposefully designed stand in 1/3rd-octave bands. The results showed that the insertion loss of the baffles depends mostly on the rubber granule board density. Increasing the density of the rubber board, insertion loss also increased. 5–6 dB insertion loss difference was measured between the most and the least dense rubber granule board baffles.

Aerodynamic Noise Simulation of a High-Speed Maglev Train Operating inside a Fully Enclosed Sound Barrier

The aerodynamic noise from the new high-speed Maglev train (NHMT) is significant. One way to reduce it is to use a fully enclosed sound barrier (FESB). This paper studies the aerodynamic noise characteristics of the NHMT operating inside a FESB at 600 km/h, taking into account the compressibility of air and the quadrupole sound sources. The transient flow field around the NHMT is simulated by adopting an improved delayed detached-eddy simulation. According to Lighthill acoustic analogy theory, the aerodynamic noise inside and outside the FESB can be simulated using the acoustic finite element method. The sound insertion loss (IL) of the FESB is analyzed by comparing the noise outside the FESB with the noise generated by the NHMT operating on open tracks. The results indicate that the noise is distributed in the streamlined shoulder area of the head and tail car and the wake. The far-field noise belongs to broadband noise, and the noise outside the FESB is similar to an incoherent line source. The IL of the FESB is 25.2 dB(A) at 25 m from the track centerline and 3.5 m above the track surface. Therefore, the noise reduction effect of a FESB is much better than a traditional upright sound barrier.

Use of viscoelastic polymer sheet as an acoustic control treatment in ceramic tiles to improve sound insertion loss

Ceramic tiles are commonly used in non-structural components of a building such as walls, partitions, floors, and roofs. However, due to their high surface hardness and density, ceramic tiles are not an ideal soundproof material. To improve the sound properties, this study introduced the use of a viscoelastic polymer sheet (VPS) as an acoustic control treatment. The VPS was attached to ceramic tiles in 4 different patterns: X, Cross, Corner, and Strip. The ceramic tiles with VPS were tested for the damping property and sound insertion loss (IL) and then compared to the ones without VPS. Results indicated that the attachment of VPS improved the damping property of the ceramic tiles. All tiles with VPS exhibited higher damping loss indexes than the ones with no VPS. The highest damping loss index of 0.017–0.018 was observed in the specimens with VPS in X and Cross patterns. In the case of IL, the performance of all ceramic tiles was indifferent when tested at sound frequencies smaller than 1000 Hz. At the sound frequencies above 1000 Hz, the best performance was observed in the specimen with VPS in the Cross pattern, followed by X, Strip, and Corner patterns, respectively. This concluded that the use of VPS can improve the damping property of a ceramic tile which also leads to the improvement in sound insertion loss.

Experimental investigation of mechanical, acoustic and hybrid metamaterial designs for enhanced and multi-band electric motor noise dissipation

Acoustic metastructures exhibit an unprecedented ability to arbitrarily manipulate the properties of sound waves, including amplitude and phase modulation which has attracted much attention in both the academic and industrial communities. Design of metastructures has been extensively investigated for the purpose of the independent manipulation of acoustic and elastic waves. It is up to now unclear however if the optimal dissipation approach involves locally resonant structural elements, or locally resonant acoustic cavities or a hybrid mix of both noise abatement mechanisms. To study this problem, we investigate numerically and experimentally the noise reduction performance of acoustic and mechanically locally resonant structures and how they perform when integrated into the same application scenario. Taking the noise emission of an electric motor as the excitation regime for our study, the acoustic and mechanical metamaterial structures with respective C-shape and T-shaped resonators are judiciously designed to maximize noise dissipation within two targeted frequency bands where the motor noise peaks. A hybrid structure with a mix of both resonators is also designed. The results demonstrate that all three metastructure designs improved the noise attenuation performance with an additional sound insertion loss of up to 16 dB when compared to a flat wall structure of equivalent mass. The findings in this work demonstrate that significant noise attenuation can be obtained by incorporating these acoustic and mechanical meta-atoms into a wall architecture which may have great potential for real world applications such as surrounding electric motors which tend to emit monotonic and irritating noise.

The exploration of transmission property by using the circular-interface types of porous acoustic metamaterials

Based on the generalised Snell’s law, many planar-interface types of acoustic metamaterials have been proposed and extensively used. However, circular-interface types of acoustic metamaterials (CAMs) that could be applied to aero-engine intakes and aircraft fuselages have not been extensively explored. Porous CAMs have been explored theoretically, numerically, and experimentally to investigate their acoustic properties, such as wave-front modulation and insertion loss, in this research. The analytical equation that governs the sound refraction of cylindrical waves through CAMs is derived based on the principle of stationary phase for the first time. In the numerical study, two types of porous CAMs with various geometries that generate periodically linear phase gradients are applied to circular interface structures. Results indicate that the excitation of high-order wave modes in the transmitted sound pressure field is dependent on the angular distance over one period of porous CAMs. When this parameter goes below critical values, the high-order wave modes in the transmitted sound pressure field will be converted into evanescent surface waves. Consequently, the sound insertion loss of porous CAM is significantly enhanced compared to that of uniform melamine foam of the same thickness. Based on the analytical and numerical study, technical guidance is proposed for designing porous CAMs with defined radii and dominant frequencies, taking compensation factors into account. This study offers a technical method for extending the industrial applicability of acoustic metamaterials from a planar interface to a circular interface.

Acoustic performance of sonic metacage consisting of Helmholtz’s resonator columns with internal partitions

The quest for a quiet environment has led to numerous efforts to shield noise at the source or develop an efficient acoustic proof system. We present a three-dimensional sonic crystal acoustic metacage structure for hybrid purposes of noise shielding and natural ventilation. The metacage prototype comprises sixteen cylindrical sonic crystal column structures (C2 and K2 types) placed at a regular distance along the circular periphery. Each column consists of two semi-cylindrical long cavities with slit channels, which allow the sound wave to enter the Helmholtz cavities and are responsible for sound attenuation. Numerical simulations and experimental measurements are used to demonstrate the efficacy of the acoustic metacage. Experimental measurements display the maximum sound insertion loss values of 20.8 dBA and 11.9 dBA for K2 type sonic crystal metacage, respectively, when the sound source is placed outside and inside the cage. For C2 type sonic crystal metacage, two sound insertion loss peaks with maximum values of 19.8 dBA and 10.4 dBA have been achieved at 2500 Hz when the sound source is kept outside and inside. The numerical results suggest the frequency tuning capabilities by adjusting the metacage size. Also, the modular design features enable the tunable operating frequency to meet different requirements.

Acoustical performance of ventilated aluminum T-slot columns-based sonic cage

This study demonstrates a modular, compact, and lightweight sonic cage for sound mitigation applications. The design prototype utilized the principle of sonic crystals and has been composed of periodically arranged readily available aluminum extrusion T-slot columns. The preliminary design has demonstrated a sound insertion loss peak of 2.94 dB at 2000 Hz, while a broad insertion loss spectrum has been obtained in 630–1000 Hz. Additionally, to improve the low-frequency performance, two additional design strategies utilizing the characteristics of T-slots have been proposed. The experimental results have revealed the significant improvement of sound insertion loss peak values in low-to-mid frequency. With design strategy I, an insertion loss peak value of 10.2 dB was observed at 500 Hz, while with design strategy II, two significant insertion loss peaks of 7.26 dB and 10.33 dB were observed at 800 Hz and 2000 Hz. Moreover, the proposed designs have revealed the tunable insertion loss peaks frequency. The designed insertion loss peaks demonstrated the feasibility of the sonic cage concept for mitigating the noise sources.

Sound insertion loss modelling for spark arrestors using two-port theory with experimental verification

Sound insertion loss modelling for spark arrestors using two-port theory with experimental verification

Experimental study on the insertion loss of multilayer panels featuring a periodic structure

Acoustic panels with different configurations (layered structure with different absorbing materials) are broadly used to attenuate the noise. Multiple panels are preferred due to the presence of multiple air cavities and the repeated reflections which lead to increased sound attenuation. The paper presents an experimental study of sound propagation through multiple panels. A novel design of acoustic panel is proposed by incorporating the sonic crystal in the air cavities of the panel. Sonic crystal (SC) consists of a periodic arrangement of sound hard scatterers which provide the sound reduction in a particular frequency range due to destructive interference in periodic scatterers. The results are based on experimental observations which are supported by the literature. The results show that increasing the number of panels increases the sound insertion loss from the multiple panel structure. However, the panels with air cavity suffer from the sound insertion loss dip, which makes the panel ineffective. The novel acoustic panel (double and triple panel with SC) provides an additional sound reduction due to SC which can be tailored for certain frequency band. For the present case, SC is designed to overcome the insertion loss dip. The novel panel provides an additional insertion loss, reaching a maximum value of 19 and 11 dB, respectively (for the double and triple panel), overcoming the insertion loss dip due to structural vibration.

Sound Insertion Loss of Kenaf and Arenga Pinnata

Heat Ventilation Air Conditioning System (HVAC) is designed to control the environment inside of residential, commercial or industrial buildings by controlling temperature of a room through heating and cooling. However, due to its mechanism, noise is produced in the system and reaches the people inside the building, thus causing distraction, discomfort and uneasiness. There are HVAC silencers in the market; however, the sound absorbing material used is of mineral wool types. In this study, the ducting silencer with the sound absorptive material that made of Arenga Pinnata, Kenaf and composition of these both materials were tested to identify its performance. The experiment was carried out in a testing apparatus that follows the ASTM E477-99 standard. Insertion loss was analysed at the end of the study. From the overall result and comparison, the insertion loss of Kenaf is averagely better than Arenga Pinnata, that is 97.5% higher than Arenga Pinnata. When composition of Arenga Pinnata and Kenaf is used, Kenaf plays important role in sound insertion loss, where when Kenaf composition increase, it increases the sound insertion loss capability.

Sound barriers from materials of inhomogeneous impedance.

Sound barriers are extensively used in environmental noise protection. However, when barriers are placed in parallel on opposite sides of a sound source, their performance deteriorates markedly. This paper describes a barrier made from materials of inhomogeneous impedance which lacks this drawback. The nonuniform impedance affects the way sound undergoes multiple reflections, and in the process traps acoustic energy. A proposed realization of the barrier comprises a closely spaced array of progressively tuned hollow narrow tubes which create a phase gradient. The acoustics of the barrier is theoretically examined and its superiority over conventional barriers is calculated using finite element modeling. Structural parameters of the barrier can be changed to achieve the required sound insertion loss, and the barrier has the potential to be widely used in environmental noise control.

OPTIMAL DESIGN ON ONE-LAYER CLOSE-FITTING ACOUSTICAL HOODS USING A SIMULATED ANNEALING METHOD

High noise levels in a multi-noise plant can be harmful to workers and will not only lead to psychological but also to physiological ailments. Consequently, noise control of industrial equipment becomes vital for workers. The study focuses on shape optimization of space-constrained close-fitting acoustic hoods. In this paper, a sound insertion loss used for evaluating the acoustic performance of an acoustical hood will be adopted. Numerical assessments of case studies for depressing the broadband noise emitted from motor-driven equipment by optimally designing a shaped one-layer close-fitting acoustic hood within a space constrained situation will be introduced. Additionally, simulated annealing (SA), a robust scheme used to search for the global optimum of a one-layer close-fitting acoustic hood by imitating the metal's heating process, was used during the optimization process. Before dealing with a broadband noise, the maximization of sound insertion loss (IL) with respect to a one-tone noise was introduced for a reliability check on the SA method. Also, an accuracy check on the mathematical model was performed. This paper, by using a simulated annealing method, presents an optimally designed one-layer close-fitting acoustic hood to provide a quick and effective method to reduce the noise level of the equipment.

Sound Attenuation Devices for Dogs Barking (Estimation of Aperture Ratio and Experimental Study of Silencer)

This paper reports a natural ventilation silencer for an animal cage having considerable sound insertion loss. Many veterinary hospitals face a serious problem that hospitalized animals are stressed from the barks of other dogs in the hospital. To address this problem, a solution that barely affects caged dogs’ health is required. First, we estimated aperture ratio of the silencer device which was considered by physiological sustainability of dog. Next, we attempted to use a silencer with sound insertion loss by attaching it to an opening side of the cage. We constructed the tested prototype silencers by using the resonance of a rectangular room and a nonwoven fabric. We measured the acoustic characteristics of the silencers that were attached to the real scale model of the animal cage. We also measured their insertion loss by considering the estimated frequency characteristics of the dogs’ barking sound. The result shows that proposed silencers have more than 10 dB insertion loss; therefore, they can maintain respiratory environment of a caged dogs along with good visibility.

Numerical Assessment of Optimal Equipment Allocation and Close-Fitting Acoustical Hoods Within a Multi-Noise Plant Using an Artificial Immune Method

High noise levels in a multi-noise plant can be harmful to workers and can lead to both psychological and physiological problems. Consequently, noise control work on equipment such as acoustic hoods becomes vital. However, research work of shape optimization on space-constrained close-fitting acoustic hoods has been neglected.In this paper, a sound insertion loss used for evaluating the acoustic performance of an acoustical hood will be adopted. A numerical case for depressing the noise levels at the receiving points along the boundary of three kinds of multi-equipment plants by optimally designing a shaped one-layer close-fitting acoustic hood and reallocating the equipment within a constrained space will also be introduced. Moreover, an artificial immune method (AIM) is adopted and coupled with the equations of sound attenuation and minimal variation square in conjunction with a twelve-point monitoring system.Consequently, this paper provides a quick and effective method for reducing the noise impact around a plant by optimally designing a shaped one-layer close-fitting acoustic hood and reallocating equipment within the AIM searching technique.

Noise barriers with varying cross-section optimized by genetic algorithms

The efficiency of a noise barrier largely depends on its geometry. Besides the height of the barrier and its top element form, the cross-section of the barrier contributes to its performance as well. The Boundary Element Method is often used as the numerical tool for simulating the behavior of proposed barrier shapes, both in 2D and 3D spaces. This paper deals with the optimization of barrier cross-section, not only by taking into account its acoustical performance (sound insertion loss), but also considering the economic feasibility of using various materials and various shapes for building the barrier. Therefore, the economic feasibility coefficient is defined and used as a final numerical value for comparing the overall efficiency of barrier design. The optimization process is done by using a genetic algorithm. Five basic forms of barrier elements and five building materials were pre-defined and characterized for the optimization process. The number of candidate units in the starting population was varied in order to examine the influence of population size on the final results. Barrier performance was evaluated for a point sound source in a 3D simulation space, and both its total rating based on the economic feasibility coefficient and its acoustical performance itself were evaluated and compared to a reference concrete barrier of the same height.

예인 음탐기 콘솔의 냉각 배출 홴 소음 저감을 위한 소음기 개발

The indoor noise of the naval vessel is very important related to the optimum environmental conditions for crews as well as the ability of fighting power of antisubmarine. Especially, sonar equipment room is one of the rooms where require to be silent because the informations of the underwater noise are collected and analyzed in there. In this paper, the sound reduction of the TASS console, one of the main noise sources in a sonar equipment room for a typical naval vessel, is described. The noise source of this TASS console is the flowing noise of cooling fan. In order to reduce this kind of noise, the plenum chamber and acoustic elbow were developed. Related to the development of the plenum chamber, the area of the air-outlet and sound absorption of the inner lining were investigated experimentally with the evaluation system of the sound insertion loss. Acoustic elbow was also manufactured and evaluated with the evaluation system of the sound insertion loss. Finally, in order to evaluated the ability of noise reduction of the plenum chamber and acoustic elbow, the indoor noise of the sonar equipment was measured when they were appled to TASS console.