Noise & vibration damping
Noise and vibration damping systems on railway vehicles reduce the sound energy radiated from wheel-rail contact, structural resonances, and mechanical sources to comply with exterior emission limits and improve the onboard acoustic environment.
Wheel-rail rolling noise is generated by surface roughness at the contact patch exciting vibrations in the wheel and rail, which then radiate as airborne sound.
Rolling noise and the wheel-rail interface
At speeds above 60 km/h it is the dominant exterior noise source for electric traction units and coaches. Its intensity depends on three factors: wheel roughness, rail roughness, and the dynamic stiffness of the wheel and rail structures.
Wheel dampers address the wheel contribution directly. Ring dampers — constrained rings of viscoelastic material fitted in a groove on the inner face of the wheel rim — attenuate vibration at frequencies above approximately 2,000 Hz, where wheel radiated noise is most significant. Constrained-layer damping patches applied to the wheel web achieve similar attenuation at frequencies above 2,000 Hz.
Resilient wheels, in which the wheel rim is connected to the hub through an elastomeric insert rather than a rigid steel disc, are standard on tramway and metro vehicles operating in urban environments with tight curves. The resilient element attenuates both rolling noise and curve squeal.
Brake block technology and freight noise
Freight wagon rolling noise is strongly influenced by tread brake block material. Cast iron blocks roughen the wheel surface through repeated braking contact, increasing rolling noise by 8–10 dB(A) compared with wheels maintained by disc brakes or composite blocks.
TSI Noise (EU 1304/2014) sets pass-by noise limits that cast iron-braked wagons cannot meet, requiring composite K-blocks on all new wagons. Retrofitting existing wagons with LL-blocks achieves equivalent noise reduction and is the primary mechanism through which the European freight fleet is being brought into compliance.
Structural damping and secondary sources
Interior noise in passenger vehicles is controlled through structural damping of the carbody shell, resilient mounting of mechanical equipment, and acoustic absorption in interior panels.
Carbody shells use constrained-layer damping materials applied to steel or aluminium panels to suppress resonance in the frequency range 100–500 Hz where structural radiation is most significant. Underfloor equipment — traction converters, compressors, cooling fans — is mounted on anti-vibration isolators that attenuate transmission of mechanical vibration to the carbody.
TSI NOI sets interior driver’s cab noise limits measured under EN 15892:2011. Exterior pass-by noise is measured under EN ISO 3095:2013 at 7.5 m from the track centreline.