On the repeatability of reflection index measurements on noise barriers

Long sequences of repeated measurements of Reflection Index measurements, following an improved version of the CEN/TS 1793-5, have been performed on a noise barrier, in order to evaluate the repeatability of the method. The considered improvements take into account the geometrical divergence, the sound source directivity, the use of a square microphone array instead of a single microphone and improved signal analysis in order to get an optimal signal subtraction of the free field response from the reflected one. The measurements have been done in laboratory on a real scale noise barrier, alternatively made very reflective or very absorptive. In some cases a disturbing fan was switched on close to the microphones. Variations of the Reflection Index values due to the unavoidable displacements of the sound source and of the microphone array from their nominal positions, to turbulence noise added by the fan are analyzed.