A rolling tyre will radiate noise in all directions. However, conventional measurement techniques for the sound absorption of surfaces only give the absorption coefficient for normal incidence. In this paper, a measurement technique is described with which it is possible to perform in situ sound absorption measurements for oblique incidence. The measurements are performed with a small microphone array, the 8p-probe, and the theory is based on the local plane wave assumption.udIn this paper, an approach is proposed to determine whether a surface behaves as a locally reacting surface or a nonlocally reacting surface, which is an important characteristic for optimising asphalt pavements for noise reduction and for modelling techniques.udMeasurements at various angles of incidence are performed to demonstrate this approach as well as measurements of the absorption coefficient at normal incidence to validate the 8p-probe with impedance tube measurements.
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