A practical method to determine the sound power of railway rolling noise using one-microphone recordings

Noise immission level depends not only on the sound power level of noise source(s) but also the associated propagation attenuation, which in turn depends on the distance, the source height(s), the receiver height, the terrain profile, the ground impedance(s), and the weather conditions. To collect all these information for determining the propagation attenuation will lead to a complicated measurement procedure, which is desired to simplify.In the European Imagine project we propose a practical method to determine the sound power of railway rolling noise using one-microphone recordings. Using a standard measurement position (7.5m from the track centre and 1.2m above railhead) the time history of the sound pressure level of a train passage will be recorded. When choosing the special time interval Tp and calculating the equivalent sound pressure level for this time period, the corresponding sound power level can easily be obtained by using the tabled constants. Applying this method to determine the sound power level one needs only to record the sound pressure level of train passages. The measurement procedure is much simplified.To limit errors this method requires a railway bed of a height between 0 and 2m above a roughly flat terrain that the ground impedance value(s) is not less than 200 kPas/m^2. Wind speed should be less than 5 m/s and a train length not shorter than 70m. In real life these requirements can easily be satisfied so the method is really practical