Comparison between laboratory and in-situ methods for measuring sound absorption properties of noise barriers

The REFLEX project was funded from 2013 to 2014 by the national road and rail Administrations (ASFINAG, ÖBB-Infrastruktur AG), the national Ministries for Transport and for Environment (BMVIT, BMFLUW) and federal states (Upper Austria, Styria, Carinthia, Tyrol and Vorarlberg). The project was led by the Austrian Institute of Technology AIT and involved 8 different Austrian noise barrier manufacturers as well as two scientific partners (AIT and the company TAS). The main scope of the REFLEX project was to investigate the reflection properties of different noise barriers for the specific case of the Austrian market with special attention to neighbouring countries. The research considered laboratory measurements according to EN 1793-1, in-situ measurements in the near field according to CEN/TS 1793-5 and far-field measurements in a distance of 25 meters from the barrier. The results of the laboratory method and the in-situ method were compared to the far-field results. The newly developed QUIESST method was also used to test the different noise barriers. Additionally, also BEM-simulations have been performed in order to validate the results obtained. This paper will focus only on the comparison between the laboratory method according to EN 1793-1 and in-situ methods for measuring sound reflection properties of noise barriers (according to CEN/TS 1793-5 and to the new developed QUIESST method), not only for the so-called single number ratings, but also for the frequency spectra. All analyses have been performed for the standardized noise spectrum for road traffic according to EN 1793-3as well as considering the newly proposed spectrum for railways according to FprEN 16272-3-2.