Author(s): Fuchs Andreas, Conter Marco , Wehr Reinhard
The number of measured reference positions for the in situ measurement of the sound reflection under direct sound field conditions according to EN 1793-5 for road traffic noise reducing devices (e.g. noise barriers) depends on the surface structure of the device under test. In the current version of the standard a noise reducing device is considered flat, if the depth of its surface structure is smaller than 85 mm and therefore only one reference position of the measurement grid is required. According to this definition, nearly all installed noise barriers along Austrian motorways are considered flat and should be measured with one reference position only. Nevertheless, the statistical analysis of over 50 sound reflection measurements of typically used flat noise barriers shows partly significant differences for the obtained single and third-band values for different reference positions. These deviations may occur for definite surface structures (e.g. concrete wood noise barriers) as well as for planar surface structures like perforated metal plates (aluminum cassette noise barriers). Therefore, to reduce the measurement uncertainty for the repeatability of the measurement procedure according to EN 1793-5 it may be advisable to use more than one reference position for flat homogeneous noise barriers.
Name: Mr Andreas Fuchs