# A Simple Method to Estimate the In Situ Performance of Noise Barriers
###### Abstract  
Noise barriers are usually classified attending to their intrinsic acoustic characteristics. This is standardized by the European Standards EN 1793, parts 2 and 6, in which a single parameter, \(DL_{R}\) or \(DL_{SI}\), is defined in order to quantify the sound insulation performance of noise barriers. However, the final performance of a noise barrier, quantified by the so-called insertion loss, \(IL\) is not only dependent on the insulation provided by the noise barrier, but it is as well affected by geometrical aspects and the acoustic characteristics of the environment where these noise-reducing devices are placed. In this work, we explore the relationship between the insertion loss and the acoustic insulation by means of numerical methods. Moreover, the authors propose a simple way to predict the insertion loss from a purely acoustic numerical simulation in which this parameter is obtained for a completely rigid noise barrier, and knowing the noise barrier's sound reduction index, in one third octave bands. noise barriers; performance; numerical simulation +
Footnote †: journal: Applied  
0000-0002-4000-33300-3300-3300-3300-3300-3300-3300-3300-3300-3300-3300-3300-3300-3300-3300-3300-3300-3300-3300-3300-3300-3300-3300-3300-3300-33300-3  
where \(L_{i}\) are the values of the normalized traffic noise spectrum, given by the standard EN 1793-3 [3], and \(R_{i}\) are the one third octave band values of the sound reduction index of the noise barrier, described in standard EN 10140-2 [4]. Following the recommendations of this measurement standard, it is valid only in the case of reverberant conditions, i.e., the sound field impinging the noise barrier is diffuse. Nevertheless, it is still used in some countries due to the problems associated with in-situ measurements, i.e., ambient noise, complicated signal processing, need for microphonic arrays, etc. A second method to quantify the sound insulation provided by the noise screen is described in the standard [2]. This standard describes an in-situ test method in which measurements are carried close to the barrier. An appropriate temporary windowing (Adrienne temporal windows) is used to avoid the problems associated with edge diffraction. The single-number quantity to estimate the overall sound insulation defined in that standard is the following:  
\[DL_{SI}=-10\ \log\left[\frac{\sum_{i=m}^{18}10^{0.1L_{i}}10^{-0.15I_{i}}}{ \sum_{i=m}^{18}10^{0.1L_{i}}}\right]\text{dBA} \tag{2}\]  
where \(L_{i}\) are the values of the normalized traffic noise spectrum, given by the standard EN 1793-3 [3] and \(SI_{i}\) are the one third octave band values of the sound insulation index derived from in situ measurements. One of the problems associated with this standard is the existence of a limiting frequency below which measurements are unreliable due to the limited length of the Adriane window used to avoid edge diffraction. The height of the barrier determines the value of this cut-off frequency. In any case, the final performance of the screen is not only dependent on the acoustic insulation but also on the particular geometry (shape of the ground, position of the sound source and listeners, and shape of the noise barrier) and other aspects, such as the ground acoustic absorption.