PROCEDURE FOR MEASURING THE SOUND ABSORPTION OF ROAD SURFACES IN SITU

As low-noise surfaces become an option more and more common in traffic noise control, a test method is required for measuring i situ the sound absorption of road surfaces. The method can be used for the determination of the absorption coefficient of road surfaces currently in use, as well as for the comparison of design specifications with current performance data after completion of the construction work. The paper presents a method, to be included in a future ISO standard, based on the use of a sequence of impulses as test signal. This allows the acquisition of the impulse response of the material under test in situ. Depending on the selected test signal, it is possible to obtain valid results in presence of high level of non-stationary background noise. While an absolute calibration of the measurement system is not needed, a reference measurement is recommended. The paper presents the comparison of the results obtained on a porous pavement, by two institutions (DIENCA and LCPC) using different test signals and post-processing softwares. The results show an encouraging good reproducibility and compare well on a wide frequency range with the predictions of a theoretical model of the acoustic behaviour of porous surfaces.