Insertion Loss Of Noise Barriers Research Articles

Insert loss experiment and acoustic impedance theoretical study on the noise barrier with MPP-QRD top structure

The effective edge processing is the key to the performance of noise barrier. To prevent the sound diffraction within the low-medium frequency range, the quadratic residue diffuser (QRD) was combined with microperforated panel (MPP) in this study. The impedance of MPP with different parameters and QRD structure with N = 7 was calculated respectively and the matching degree of the composite structure was obtained. The insertion loss of noise barriers with different MPP-QRD top structures was field measured and compared to the equi-height vertical noise barrier. The results show that the degree of impedance matching between microperforated panels and quadratic residue diffusers is significantly correlated with their performance as the top structure of noise barrier. The acoustic impedance matched MPP-QRD top structure can significantly improve the insertion loss of the vertical noise barrierwith the same height. When the microperforated panel perforation is 3 %, the thickness is 0.8 mm, and the aperture is 0.6 mm, performance of the MPP-QRD structure is the best, the relative insertion loss can reach 4.07 dB.

Estimation of insertion loss for noise barrier with multichannel sound reproduction technology

A method based on the wave field synthesis is proposed to estimate the insertion loss of a noise barrier under the complex diffracted sound field due to the characteristics of the noise source and the transmitted sound through the barrier. This method is equivalent to evaluating the acoustical performance of the noise barrier in a reproduced sound field. There are two advantages of the proposed method. First, by storing the radiated sound of various noise sources as a database in advance, the insertion loss for them can be obtained. Second, the impulse responses from multipoint can be measured by changing one loudspeaker position sequentially, so it does not necessarily require many loudspeakers. In order to validate this method, numerical simulation was performed for a diffracted sound field consisting of a point source and a rigid barrier. Moreover, the insertion loss of simple noise barriers for one loudspeaker was estimated under the primary and synthesized sound field conditions experimentally. As a practical example, the insertion loss of the same noise barriers for a moving automobile was also estimated. The results show that the estimation error is within a few decibels in the frequency band where spatial aliasing does not occur.

Optimisation of railway noise barrier design using finite element and boundary element modelling methods

The prediction of environmental noise barrier insertion loss (IL) is commonly undertaken from widely available empirical methods derived from measurements and geometrical acoustic approximations. The accuracy of these methods is limited when analysing non-standard design parameters, such as geometry; characteristics and location of sound absorbing materials; or diffraction effects close to the barrier. This article presents a new methodology to optimise the design of a railway noise barrier using a simplified numerical method. The numerical method is based on a two-dimensional hybrid finite element and boundary element analysis. The numerical method has been calibrated and tested against measurements of high speed trains. The model assumes an infinitely long train with pre-defined sound sources (e.g. rolling source, body aerodynamic, etc.). The numerical model quantifies the effect of various parameters upon the barrier IL including material properties; area and location of sound absorbing materials; diffraction over the barrier top; and analysis of energy build-up between train and barrier. These parameters are not easily quantifiable using standard methods and hence the innovation aspect of the methodology. The outcome of this study can be used to optimise and improve confidence in the detailed design of complex noise barriers.

Determination of Insertion Loss of noise barriers in Spanish roads

The evaluation of the effectiveness of noise barriers have addressed, in some research studies, the intrinsic characteristics of barriers, such as noise absorption or transmission; in other studies, it has been based on the global characteristics of Insertion Loss (IL), which is defined as the difference in the noise level before and after the installation of the barrier. IL is an extrinsic characteristic of noise barriers, depending largely on the site in which the barrier is placed. This research investigated the in situ effectiveness of existing noise barriers by using the indirect IL method established in the international standard ISO 10847:1997. Measurements were performed at thirty sample sites, distributed among the three most frequent types of material found on Spanish roads (earth berms and concrete and metal walls).The results revealed moderate IL values. Results at a distance of 25 m were clearly below the expected effectiveness of a noise barrier. The IL values for the three types of barriers were similar. The best noise reduction effect was in the frequency range of 125–8000 Hz, at which the traffic noise is dominant. In most cases, the dimensions of the barriers did not seem to have been determined taking into account diffraction requirements.

Finite Element Method for the Estimation of Insertion Loss of Noise Barriers: Comparison with Various Formulae (2D)

Noise barriers are a critical part of noise mitigation in urban and rural areas. In this study, a comparison of the insertion loss calculations of noise barriers via the Finite Element Method (FEM) and various formulae (Kurze–Anderson, ISO 9613-2/Tatge, Menounou) is presented in the case of two-dimensional acoustic radiation problems. Some of the cases explored include: receiver in the illuminated zone, in the shadow zone, in the shadow border, source in medium, long, short distance from the barrier, source and receiver near barrier, and source above the barrier. Comparisons of the results indicate that FEM results comply well (less than 1 dB in each case) with Menounou’s formula which in turn complies with the analytic solution (MacDonald Solution). In certain cases, the differences between FEM and Menounou’s formula compared to Kurze–Anderson and ISO 9613-2/Tatge formulae are substantial (source and receiver near the barrier (10 dB) and source near the barrier and receiver in the shadow border (5 dB)). Similar differences are also confirmed by the analytic solution. The findings suggest that FEM can be applied effectively for the precise estimation of the insertion loss of noise barriers. Especially in cases where ISO 9613-2 formula shows large deviations from the analytic solution (e.g., near barrier), possible applications may arise in cases such as balconies, facades, etc. Furthermore, the study supports the idea that FEM could possibly be effectively utilized in real life applications for microscale urban acoustic modeling as a viable alternative to expensive noise prediction software.

Study of metadiffusers in broadband improvement of noise barrier performance

In previous studies, installation of Schroeder diffusers on top of noise barriers has been shown to improve effectiveness of noise barriers. However, since these diffusers have thickness of the order of design wavelength, they become very bulky, costly and less practical to use. Their use for lower frequency applications is thus limited. Metadiffusers are subwavelength diffusers, capable of creating similar diffusion characteristics, but their thickness can be 10 to 20 times lower than conventional diffusers. In addition, the absorption performance can be improved by incorporating coupled Helmholtz resonators to further increase noise barrier insertion loss. The reduced thickness and incorporation of Helmholtz resonators enables better performance for a broader range of frequencies, which was not possible with a conventional sound diffuser. It was observed that both 1-D and 2-D metadiffuser designs installed on top of noise barriers improve the performance upto 5dBA in the shadow zone. A combination of number sequences such as maximum length, quadratic residue, primitive root, Luke, ternary, etc. with Helmholtz resonators tuned to different frequencies has also been reported in this study.

Improved Methods for In-situ Measurement Railway Noise Barrier Insertion Loss

Many countries which seek to understand the acoustic performance of railway noise barriers have established standards for the conduct of in-situ experiments. However, there are no universally acknowledged receiver positions for the evaluation of the barrier performance, a fact which may be leading to uncertainty over the noise reduction capabilities of available barriers. In terms of the descriptor of the barrier performance, the general recommendation is the A-weighted sound pressure level, although the latter is considered to underestimate low frequencies for railway noise barrier. Thus, in this study, the comparison of receiver positions and the descriptors among existing Chinese, ISO and European standards were investigated. Based upon a combination of diffraction theory and standards, a rearrangement of receiver positions and one-third-octave-band analysis were proposed. In addition, in line with improved methods, an in-situ measurement of insertion loss for a 1.5m high railway noise barrier was designed and conducted. The results of the experiment validate as effective and applicable the new receiver positions. These results also suggest that one-third-octave-band analysis is indispensable.

Calculation of Noise Barrier Insertion Loss Based on Varied Vehicle Frequencies

A single frequency of 500 Hz is used as the equivalent frequency for traffic noise to calculate the approximate diffraction in current road barrier designs. However, the noise frequency changes according to the different types of vehicles moving at various speeds. The primary objective of this study is the development of a method of calculating the insertion loss based on frequencies. First, the noise emissions of a large number of vehicles classified by speed and type were measured to obtain data the noise spectrum. The corresponding relation between vehicle type, speed, and noise frequency was obtained. Next, the impact of different frequencies on the insertion loss was analyzed and was verified to be reasonable in experiments with different propagation distances compared to the analysis of a pure 500 Hz sound. In addition, calculations were applied in a case with different traffic flows, and the effect of a road noise barrier with different types of constituents and flow speeds were analyzed. The results show that sound pressure levels behind a barrier of a heavy vehicle flow or with a high speed are notably elevated.

Deriving correction functions to model the efficiency of noise barriers with complex shapes using boundary element simulations

The boundary element method (BEM) is a commonly used method to compute the insertion loss of noise barriers having arbitrary cross-sections. For large scale three-dimensional problems, however, the BEM is not feasible. On the other hand, standardized calculation methods for noise mapping are efficient, but shapes other than the straight barrier cannot be properly calculated. Attempts to merge these two approaches by using BEM to derive correction functions based on geometrical quantities such as source and target angle as well as the path length elongation between source and receiver caused by the barrier were usually focused on a small set of barrier types, dimensions, absorptive configurations, source or receiver positions. The main objective of this study is to investigate which functions based on the most common geometrical parameters are well suited for approximating the efficiency of different types of barriers, dimensions and absorptive configurations. To achieve this, numerous combinations of 7 different barrier types, different heights and widths as well as 3 different absorptive configurations were simulated using the 2D BEM for 8 different source positions. The octave-band-wise efficiency, i.e. the frequency-dependent gain in insertion loss compared to an equally high, fully reflective straight barrier was used as a basis for the correction functions. Linear as well as polynomial models were compared yielding a polynomial of third degree in the source and fourth degree in the target angle as the best model. Effects on the error using uniform sampling in the target angle instead of a uniform receiver grid as a basis for the correction functions are also investigated. Furthermore, wide-band efficiencies based on standardized traffic emission spectra are calculated showing small errors compared to single-band errors, in particular in the high-frequency range. A linear interpolation scheme is suggested to deal with barriers having dimensions not simulated in this work.

Insertion Loss of Noise Barriers on an Aboveground, Full-Scale Model Longwall Coal Mining Shearer

The U.S. mining industry struggles with hazardous noise and dust exposures in underground mining. Specifically, longwall coal mine shearer operators are routinely exposed to noise levels at 151% of the allowable daily dose, and approximately 20% exceed regulatory dust levels. In the current study, a partial barrier was mounted on the full-scale mock shearer at the National Institute for Occupational Safety and Health Pittsburgh Research Laboratory. A simulated, full-scale, coal mine longwall shearer operation was employed to test the feasibility of utilizing a barrier to separate the shearer operator from the direct path of the noise and dust source during mining operations. In this model, noise levels at the operators' positions were reduced by 2.6 to 8.2 A-weighted decibels (dBA) from the application of the test barriers. Estimated insertion loss underground was 1.7 to 7.3 dBA. The barrier should be tested in an underground mining operation to determine if it can reduce shearer operators' noise exposure to below regulatory limits.

Simulation of noise barrier insertion loss using the boundary element method

Within a project of the European Commission "Calm Tracks & Routes" the performances of different styles of noise barriers were investigated. Additionally new methods for increasing the absorption were investigated. A central theme was to investigate the mitigation of curved walls with high absorption coefficients, because studies made before the project gave the hint that noise barriers curved away from the source should give satisfying insertion loss. Due to the curvature the view in the landscape is hindered to a lesser degree compared to straight noise barriers. The investigation of the noise barriers was done by boundary element methods. An absorptive model for grassland was added and implemented into Green's functions. Due to the existence of smeared sources the application of the fast multipole method was not possible and the simulations were limited to the two-dimensional case. It became obvious that the distance of the source is important for the mitigation of curved noise barriers with respect to straight ones. Therefore different wall types and source positions were investigated. The results of the numerical simulation were compared to measurements in situ and in a large anechoic chamber.

Improving Traffic-Noise Model Insertion Loss Accuracy Based on Diffraction and Reflection Theories

This paper investigates the physical mechanisms related to highway noise barrier insertion loss, and evaluates the accuracy of insertion loss of the existing traffic-noise model, TNM 2.5, compared to STAMINA 2.0 and field measurement data. To quantify the accuracy of either TNM or STAMINA, a new Highway Noise Prediction program, HNP 1.0, was developed. The findings of the study show that from the perspective of diffraction theories, STAMINA 2.0 and HNP 1.0 predict more accurate insertion loss than TNM 2.5 based on the measurement data, and TNM 2.5 over-predicts the insertion loss by approximately 3 dBA when compared with STAMINA 2.0. By applying the assumptions used in HNP 1.0, an average of 2.5 dBA reduction of insertion loss with TNM 2.5 can be achieved. These improvements in noise prediction accuracy of insertion loss have major implications for environmental planning.

A study of sound intensity control for active noise barriers

Active noise control systems have been applied to increase the insertion loss of noise barriers where the squared sound pressure or the total acoustic energy density is used as the cost function in previous works. The absolute value of the mean active sound intensity is chosen as the cost function to obtain extra sound insertion loss in the dark area of a hybrid active noise barrier system in this note. The strategy of minimizing the near-field sound intensity at discrete locations along the edge of the passive barrier is shown to be able to provide better far-field noise reduction than that of minimizing the squared sound pressure control. Both numerical simulations and off-line experiments are carried out with a three-channel demonstration system, where the locations of the secondary sources and the error sensors are optimized and comparisons are made between the extra sound pressure attenuation of the sound intensity control and that of the squared sound pressure control.

Investigation on Insertion Loss of Noise Barrier for High-speed Moving Sound Source

Investigation on Insertion Loss of Noise Barrier for High-speed Moving Sound Source

A boundary element method for the calculation of noise barrier insertion loss in the presence of atmospheric turbulence

Atmospheric turbulence is an important factor that limits the amount of attenuation a barrier can provide in the outdoor environment. It is therefore important to develop a reliable method to predict its effect on barrier performance. The boundary element method (BEM) has been shown to be a very effective technique for predicting barrier insertion loss in the absence of turbulence. This paper develops a simple and efficient modification of the BEM formulation to predict the insertion loss of a barrier in the presence of atmospheric turbulence. The modification is based on two alternative methods: (1) random realisations of log-amplitude and phase fluctuations of boundary sources and (2) de-correlation of source coherence using the mutual coherence function (MCF). An investigation into the behaviours of these two methods is carried out and simplified forms of the methods developed. Some systematic differences between the predictions from the methods are found. When incorporated into the BEM formulation, the method of random realisations and the method of MCF de-correlation provide predictions that agree well with predictions by the parabolic equation method and by the scattering cross-section method on a variety of thin barrier configurations.

경계요소법을 이용한 간섭형 방음벽의 설계

This paper investigates the insertion loss of nosie barrier with a interference device, The efficiency of the conventional interference-type noise barrier depends on specific frequency, Thus this study is performed to improve the efficiency of the nosie barrierin the range of broadband frequency. by changing the shape of interference device and adding the channel with various depths, The boundary element method (BEM) is used to predict the insertion loss of noise barrier. Two-dimensional boundary element model is created to simulate the performance of long barrier with a line source.

A reduced-scale railway noise barrier's insertion loss and absorption coefficients: comparison of field measurements and predictions

In situ testing determined the insertion loss ( IL) and absorption coefficients of a candidate absorptive noise barrier (soundwall) to abate railway noise for residents of Anaheim, CA. A 4000 m barrier is proposed south of the tracks, but residential areas to the north have expressed concerns that barrier reflections will increase their noise exposure. To address these concerns, a 3.66 m high by 14.6 m long demonstration barrier was built in the parking lot of Edison Field, Anaheim, as part of a public open house, thereby allowing for acoustical measurements. Insertion loss ( IL) was measured in third-octave bands assuming 1/2-scale construction. The IL for three, scaled railway noise sub-sources (rail/wheel interface, locomotive, and train horn) was measured at six, scaled distances. The highest total, A-weighted IL, after corrections for finite-barrier and point-source speaker effects was 22 dB(A) for rail/wheel noise, 18 dB(A) for locomotive noise, and 20 dB(A) for train horn noise. These results can be compared favourably to IL predictions made using algorithms from the US Federal Rail Administration (FRA) noise assessment guidelines. For the actual barrier installation, shielded residential receivers located south of the project are expected to see their future noise exposures reduced from an unmitigated 78 CNEL to 65 CNEL. Absorption coefficients were measured using time delay spectrometry. At lower frequencies, measured absorption coefficients were notably less than the reverberation room results advertised in the manufacturer's literature, but generally conformed with impedance tube results. At higher frequencies the correspondence between measured absorption coefficients and reverberation room results was much improved. For the actual barrier installation, unshielded residential receivers to the north are expected to experience noise exposure increases of less than 1 dB(A). This factor of increase is consistent with a finding of no impact when assessed using FRA guidelines for allowable increases of noise exposure.

Investigation for insertion loss of noise barrier for sound source moving at high speed

Investigation for insertion loss of noise barrier for sound source moving at high speed

Investigation on insertion loss of noise barrier for high-speed moving sound source

Investigation on insertion loss of noise barrier for high-speed moving sound source

Numerical study on the insertion loss of noise barrier for coherent/incoherent line source

Numerical study on the insertion loss of noise barrier for coherent/incoherent line source