Implications of the directivity of railway noise sources for their quantification using conventional beamforming

Abstract

This paper investigates the effect of the directivity of railway noise sources on the results of an identification procedure based on beamforming using a microphone array. Usually when performing pass-by noise tests, a single-microphone noise spectrum is obtained for a time window corresponding to the length of the whole train, or of a single vehicle. In this context, a source quantification algorithm should be able to evaluate the contribution of each noise source over this time window. However, different railway noise sources have different directivities, and it is shown that these need to be taken into account to achieve accurate source quantification. By making use of monopoles, dipoles and quadrupoles, it is shown that a different compensation is needed according to the directivity. For the particular case of the noise radiated by the rail, this has a complex directivity pattern that is only partially captured by a microphone array. It is demonstrated that the overestimation of the wheel contribution found in previous research may be attributed to a misinterpretation of part of the rail contribution from the beamforming map.

Acoustic Signature and Impact of High-Speed Railway Vehicles in the Vicinity of Transport Routes

“…The beamforming method consists in processing a spatial-temporal signal recorded by a microphone array. Each microphone of the acoustic array, having a specific position relative to its centre, is assigned a time delay which allows it to focus the signal beam in the direction of acoustic wave propagation [5,19,[23][24][25][26][27]. By using a time delay, the measured signal is the same for all microphones used.…”

Aerodynamic noise of high-speed train pantographs: Comparisons between field measurements and an updated component-based prediction model

“…This was located 10 m from the centre of the track. The design of this microphone array includes 90 microphones (see [40]) mounted on a carbon fibre frame, positioned in the arrangement shown in Figure 6(b).…”

“…The effect of the compensation factor is to rescale the noise spectra estimated from the beamforming output so that they represent sound pressure spectra at the array centre averaged over the length of a single car. More details on the quantification algorithm are given in [40].…”

A Partition Spatial Filtering Method for Acoustic Array Configuration

“…Acoustic array techniques are applied for moving sources, such as cars [1], trains [2], airplanes [3][4][5], and wind turbines [6][7][8]. However, array identifying accuracy and resolution are limited by the array configuration due to complex motion sound characteristics.…”