Directivity of Railway Rolling Noise

Paper in proceeding, 2007

Directivity is an important parameter to describe a sound source. For railway rolling noise this becomes a complicated issue because its vertical and horizontal directivities depend on many factors. In this paper a complete procedure to determine the vertical and horizontal directivities of railway rolling noise in one-third octave bands has been proposed. The procedure consists of two parts: (1) to define the vertical and horizontal directivities both for track and wheel radiations; (2) to determine the effective vertical and horizontal directivities for the total railway rolling noise. For practical reasons it is better to include the shielding effect of the car-body, also the low barriers when they are present alongside a track. Since this shielding effect dominates, the inclusive vertical directivity of railway rolling noise can vary with train types, and will also be different when influenced by low barriers (such as viaducts). The horizontal directivity of railway rolling noise is determined by the horizontal directivities of the track and wheel radiations, and weighted by the relative importance of the two sub-sources which is described by the track and vehicle transfer functions. In general, the horizontal directivity of railway rolling noise varies with different vehicle-track combinations.