Beamforming technology helps reduce train noise

Reducing pass by noise of Spanish train

Railways in Spain are set to become quieter thanks to beamforming technology being used to analyse acoustic profiles of passing trains.

High-speed train manufacturer, Construcciones y Auxiliar de Ferrocarriles (CAF) has boosted its ability to reduce the noise generated by its trains, helping to make high-speed travel more viable for commuters and operators alike, with the latest beamforming technology.

High-speed trains are one of the eco-friendliest ways to travel thanks to their extremely high capacity and efficiency, but their big drawback is that they are very loud. CAF Research and development Engineer, Isaac Gutiérrez explains: “Aerodynamic noise is the most important noise contributor to the overall pass-by noise level and is the most challenging to measure and understand. We were looking for the most accurate way to do this in order to make relevant adjustments to our train design and meet the European TSI requirements.”

CAF contacted sound and vibration specialist, Brüel & Kjær, to discuss possible methods and – following a consultation – the company’s acoustic beamforming technology was identified as the best tool for CAF. Using a portable array of microphones, this technology locates noise sources in high definition, even on moving objects. It displays sound as colour-coded contours overlaid on an image of the test object.

As the acoustic dynamic range of a high-speed train passing by is very wide (it goes from almost complete silence to extremely high noise levels in just a few seconds) the beamforming technology’s wide dynamic range is ideal for recording both low and high noise levels at an immense sampling rate.

Along with assistance from Brüel & Kjær, CAF’s team set up a beamforming system with pass-by sites across the Spanish countryside. The project resulted in noise maps indicating sound pressure, pressure contribution density and sound intensity for the train as a whole and for individual parts of the train.

Isaac commented: “From studying the noise maps, we have determined that we, for example, could modify the shape of the carriages to change the direction of the air passing between them. By making this modification, we were able to reduce the exterior noise by 3 to 5 dB(A). We are confident that no other noise measurement system could have helped us achieve this.”

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