Sound Propagation over Ballast Surfaces

Abstract

Sound emission measurements of railway vehicles are usually performed with microphones close to the railway line. In case of double-track lines and vehicles on the distant track ground reflections develop mainly above the ballast bed. The uncertainty of estimated sound power based on microphone signals depends on the accuracy of considered propagation effects. It is found that ground reflection over ballast has to be understood as an extended-reaction process. With the application of a simple geometrical model for a ballast structure good agreement between measurement and calculation could be achieved. The model was validated for a large set of loudspeaker measurements conducted at the occasion of the development work of sonRAIL, the new Swiss railway noise calculation model.