Advancements in Sound Reflection and Airborne Sound Insulation Measurement on Noise Barriers

Abstract

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 [1]). After some years 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 [2]. 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.