The Journal of Industry and Technology

Industrial Analytical Instrumentation

Euro Technology

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Automotive and railway engineering

Reducing high-speed train noise for CAF

Pass-by noise is a major constraint on this economical transport, leading a Spanish train maker to adopt beamforming technology.

Leading 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 solutions 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 cars to change the direction of the air passing between the cars. 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."

The full article about CAF's challenges is available at:

Brüel & Kjær in profile
Brüel & Kjær is a world-leading manufacturer and supplier of sound and vibration measurement systems.

Brüel & Kjær help customers measure and manage the quality of sound and vibration in their products and in the environment. Focus areas are aerospace, space, defence, automotive, ground transportation, airport environment, urban environment, telecom and audio.

Brüel & Kjær has an unparalleled portfolio of sound and vibration equipment and is a long-established designer and manufacturer of innovative instrumentation including sound level meters, microphones, accelerometers, conditioning amplifiers, calibrators, noise and vibration analysers, and PULSE software.

Brüel & Kjær also design and manufacture the LDS range of vibration test systems, as well as complete airport and environmental monitoring systems: WebTrak, ANOMS, NoiseOffice and Sentinel.

To see the full range of solutions, systems and products, view website:

Brüel & Kjær runs a variety of training courses - from basic introductions to noise and its effects to more specialised classes teaching customers how to get the most out of their equipment. Free online training courses, conducted by our expert engineers, run throughout the year too.

For all course registration details visit: 
Refer to page 207

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