A Measurement Procedure for the Sound Emission of Railway Sources Including Source Separation

Abstract

A measurement method for railway noise, which yields spectral source levels for rolling noise including three-dimensional directivity information, is presented. Additionally, emission values for secondary sources as traction noise or aerodynamic noise are gathered. The method is based on two microphones and an intensity probe. The latter is placed in a way to suppress sound intensity stemming from the rail-wheel area and therefore allows secondary sources to be measured that are masked by rolling noise in the overall sound exposure. The method has been tested with a loudspeaker placed on a freight train. Various combinations of train speeds and amplitudes of the loudspeaker signal showed the ability of the method to identify secondary sources that were up to 15 dB below rolling noise with high accuracy. In a further step, traction noise from a high power traction unit was identified and the results were compared with array measurements. The tests proved the method's ability to yield input information for complex railway noise models. The fact that the method can be applied at comparably modest expense in comparison with other elaborated measurement procedures seems to be promising for further applications.