Microphone array measurements for the identification of mobile noise sources

A modern parameter in the global quality assessment of high speed trains is the noise emission. An innovative method for the identification and comparison of mobile acoustic sources was implemented: the microphone array. Basis of the method is the “beamforming algorithm” that from a measure of the acoustic pressure in several points allows to investigate the position and the characteristics of the sound source. This source can be either fixed or moving respect to the array making the method capable of separating different sources among a general noise signal perceived during a vehicle pass-by. The method was developed using numerical models and proved to be effective testing it on site with different known sound sources both fixed and moving. After these tests an application of the pass-by noise measurements generated by a rail convoy was investigated. The occasion was given by an experimental campaign settled for the evaluation of noise and vibration emission of a standard ballast superstructure, within an European research program(“HIPERTRACK”). Results showed the capability of the method to distinguish multiple sound sources. The method showed the possibility to identify the noise emitted by a single wheelset. In this paper an analysis of the noise emitted by the wheel-track interaction of different convoy typologies on the same ballast superstructure has been performed and results will be discussed. A comparison between noise and vibration recorded on the rail showed a good agreement. Time/frequency analysis was finally implemented to identify the spectrum of the emission associated with every single bogie.