This document specifies a test method for measuring in situ the sound absorption coefficient of road surfaces for the one-third octave band frequencies ranging from 250 Hz to 1 600 Hz under normal incidence conditions. If necessary for practical applications the diameter of the tube can be reduced to 80 mm. This will increase the upper boundary of the frequency range to 2 000 Hz one-third octave band (see 5.4) but reduces the area under test.

The test method is intended for the following applications:

—     determination of the sound absorption coefficient (and, if of interest, also the complex acoustical impedance) of semi-dense to dense road surfaces;

—     determination of the sound absorption properties of test tracks according to ISO 10844^[2] or other similar standards and test surfaces defined in national and international type approval regulations for road vehicles and their tyres;

—     verification of the compliance of the sound absorption coefficient of a road surface with design-specifications or other requirements.