Sound Diffraction Over Noise Barriers with Added Devices Installed on the Top Edge (original) (raw)
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Sound insulation measurements on noise barriers across their entire extension: a preliminary study
Proc. Inter-Noise 2020, Seoul, Paper 5_4_994, 1-10, 2020
EN 1793-6 allows measuring the in-situ sound insulation of installed noise barriers at selected positions, but it would be desirable to check the quality of the installation or the decrease in performance over time over the whole length of a noise barrier. For this purpose it is necessary to carry out measurements along the entire extension of the noise barrier and not just at few positions taken as representative. This work presents a preliminary study of a quick method for evaluating airborne sound insulation along the entire length of a noise barrier and finding weak points, like assembly errors. Preliminary measurements were made by moving in the horizontal direction a linear antenna of microphones, kept vertical, along the entire width of the barrier in 0.25 m steps. On the opposite side of the barrier (noise source side) a loudspeaker was held in axis with the microphones, at fixed height, for each step. The entire surface of a 9 m wide, 4 m high sample barrier was analysed. Processing the measured impulse responses between the loudspeaker and the microphones, global images of the local airborne sound insulation can be obtained in each frequency band.
Determination of Acoustic Properties of Noise Barriers
2016
Recently major improvements in the measurement methods for determining the in-situ values of noise barriers have been implemented. Laboratory and in-situ measurements have been compared. The results are not directly comparable, due to differences between the diffuse, omnidirectional sound field in the laboratory and the limited incidence angles that occur in the field. Additionally, new measurement methods have been developed by the University of Twente and SoundInSight, which are suitable to determine the acoustic properties of noise barriers in-situ, for any complex sound field.
Advancements in sound reflection and airborne sound insulation measurement on noise barriers
The in-situ measurement of sound reflection and airborne sound insulation characteristics of a noise barrier in Europe are currently performed following the CEN/TS 1793-5 European standard guidelines (last revision published in 2003 [4]). After some years and a large number of barriers measured, the original method has been significantly enhanced and validated in the frame of the EU funded QUIESST project, WP3 [5]. The sound reflection measurement method has been improved using a square 9-microphone grid not rigidly connected to the loudspeaker, an optimized alignment algorithm of free-field and reflected impulse responses, including fractional step shifts and least squares estimation of the best relative position, and a correction for geometrical divergence and sound source directivity. Each single measurement is then validated by means of the Reduction Factor calculation. The airborne sound insulation measurement method has not been markedly changed since 2003, because the procedure is robust and easily applicable as it is, but some problems may still be encountered when measuring highly insulating noise barriers, due to a poor signal to noise ratio of the transmitted impulse response. In those cases it is difficult to realize just after the measurement whether the obtained data are valid or not. A method, applicable on site, to overcome this problem is described here. It is based on the Signal to Noise Ratio estimation of critical parts of the acquired impulse responses and gives a strong validation criterion.
Experimental evaluation and optimization of the acoustic properties of a noise barrier
2002
The latest Italian laws and U.E. Directives on noise pollution have prompt attention on the acoustic performances of materials; in this field noise barriers are among the most commonly used systems to reduce noise from roads or railways, also in urban areas. The paper illustrates the measurement results obtained at the Acoustics Laboratory of the University of Perugia on a new noise barrier sample. The barrier is made of perforated metal panels, filled with rockwool; there is also the possibility to insert in the barrier transparent panels, made of PMMA (Polimetylmetacrylate). Sound insulation properties have been measured in two coupled reverberating rooms, according to ISO 140-1[1], 140-3 [2], 717-1 [3], EN 1793-1 [4] and 1793-2 [5]; measurements have been carried out for two different barriers, one all made of metal panels, the other one with an insertion of PMMA panels. Sound absorption properties of the metal panels have been measured in a reverberating room, according to ISO/D...
ACOUSTIC INTRINSIC PERFORMANCES OF NOISE BARRIERS: ACCURACY OF IN SITU MEASUREMENT TECHNIQUES
Laboratory and in situ methods have been used for measuring intrinsic performances of noise barriers, as prescribed by the European standard series EN 1793. The use of in situ techniques is promising, but their accuracy has to be duly verified, even in comparison with well-known standardized procedures. Sound insulation and reflection properties have been measured through a MLS-based technique in an outdoor test field. The paper analyzes the procedures that mainly influence the accuracy: correction for wave spreading and time windowing. Repeatability of the in situ method for sound insulation is satisfying and its results look consistent with simple prediction models. Nevertheless, in situ data can be overestimated at low frequencies, due to the overlapping of the transmitted and diffracted components. The method has to be carefully employed when the sample shows apertures as slits or holes, unless a different kind of sound propagation is assumed at the receiving side. A good agreement was found between in situ and laboratory sound insulation data, while in situ and laboratory absorption properties show poorer correlation.
The Journal of the Acoustical Society of America, 2000
In the frame of the 1994-1997 Standard, Measurement and Testing program, the European Commission funded a research project, named Adrienne, to define new test methods for measuring the intrinsic characteristics of road traffic noise reducing devices in situ. The research team produced innovative methods for testing the sound reflection/absorption and the airborne sound insulation characteristics of noise barriers. These methods are now under consideration at CEN Í‘European Committee for StandardizationÍ’, to become European standards. The present work reports a detailed verification of the test method for airborne sound insulation over a selection of 17 noise barriers, representative of the Italian and European production. The samples were tested both outdoors, using the new Adrienne method, and in laboratory, following the European standard EN 1793-2. In both cases the single number rating for airborne sound insulation recommended by the European standard was calculated. The new method proved to be easy to use and reliable for all kinds of barriers. It has been found sensitive to quality of mounting, presence of seals, and other details typical of outdoor installations. The comparison between field and laboratory results shows a good correlation, while existing differences can be explained with the different sound fields and mounting conditions between the outdoor and laboratory tests. It is concluded that the Adrienne method is adequate for its intended use.
In situ measurements of Reflection Index and Sound Insulation Index of noise barriers
Barriers employed for road traffic noise reduction can be characterized by two indices: reflection index for sound reflection and insulation index for airborne sound insulation. They can be measured following the method described in CEN/TS 1793-5 standard, based on impulse response measurements employing a pressure microphone. The method mandates for averaging results of measurements taken in different points in front of the device under test and/or for specific angles of incidence, employing the obsolete MLS signal for performing the measurements, which can cause severe artefacts due to nonlinearity and time-variance of the system. Furthermore, the CEN/TS 1793-5 standard presents some geometric problems, which could arise if the barrier does not reach a minimum height or if it has a very rough (scattering) surface. During the reflection index measurement on a barrier of limited height, the reflected sound can be contaminated by the ground reflection, compromising the fairness of the whole result. Also the insulation index can be affected by the height of the noise barrier, since the sound passing above the device under test can become mixed with the sound passing through it. It has been noticed how these practical problems, jointly with the assumption of a surface reflecting specularly in the final formula, can significantly over/under estimate the laboratory values of both the indices. Results of in situ tests based on CEN/TS 1793-5 will be shown in comparison with results obtained through a different approach, based on sound intensity measurements, and with the traditional tests performed in the lab.
The Journal of the Acoustical Society of America, 2013
The sound reflection and the airborne sound insulation of noise barriers can be measured in-situ according to CEN/TS 1793-51,2,3,4. The procedure, based on impulse response measurements close to the noise barrier and in the free field, is robust and easily applicable; it allows to get the results in real-time just after the measurements, in situ or in laboratory, applying a well defined post-processing to the raw data. Some errors may anyway occur: for sound reflection, when the signal subtraction procedure1 leaves a small residual; for airborne sound insulation, when the barrier under test is highly insulating and so the transmitted signal is very low. This kind of problems is not always easy to recognize when on site. The European standard explains the measurement procedure in details, but a criterion for validating the measurements and prevent the acquisition of possible invalid data is missing. The authors analyzed many measurements on different noise barriers, performed on outdoor test sites during an inter-laboratory test organized in the frame of the European project QUIESST5,6,7, having among its objectives the improvement of the CEN/TS 1793-5 measurement method. The analysis of this large amount of data suggested that the above mentioned measurement problems may be identified and corrected evaluating the signal-to-noise ratio (SNR) of critical parts of the impulse responses being processed. These criteria are rigorously described here for the first time and illustrative examples are presented.
The Decrease of Noise with Acoustics Barriers
sra.ro
In this paper is presented the effect of one barrier of length infinite, situated along the speedway, having effect of acoustics protection over a populated area situated behind it. The barrier doesn't cover up an area of acoustic shadow, due to sound diffraction over the superior edge. It's made a parallel between two choice variants of acoustics barriers using the sound damping calculation, from behind of barrier.