In situ measurement of the acoustic performance of a full scale tramway low height noise barrier prototype

The acoustic performance of a full scale low height barrier prototype meant to attenuate tramway noise is measured in situ. The prototype is made of an inverted L-shape assembly of pressed wood boards covered on the source side with fibrous absorbing material, and has been set up temporarily in a residential area in the town of Saint-Martin-d'Hères, near Grenoble (France), through which a tramway line passes. A series of pass-by level measurements were made at a close receiver location corresponding to the typical height of human ears, with and without the device. The tram speed has also been measured using an auxiliary microphone located very close to the track. A significant variability in pass-by levels has been found between the different trams, even when applying an approximate correction for speed. However it is shown that the barrier provides on average an attenuation of more than 10 dB(A) for the trams closest to the barrier, during the whole pass-by. Spectral analysis of the recorded signals is also carried out to estimate the barrier insertion loss more accurately. Furthermore, comparisons between measurements and BEM calculations show that numerical predictions can yield rather good estimates of the actual in situ performance, within a few dB(A).