Metro car body noise: main sources and countermeasures
Noise in urban rail vehicles comes from five areas: track vibration, braking, motors, structure-borne transmission and aerodynamics. Noise control is a systems job and has to be considered item by item.
Five kinds of source
Track vibration noise: vibration from wheel–rail contact travels along the track and is stronger in curves, at crossings and at switches. Braking noise: both mechanical and electric braking make noise, as does friction between brake and wheelset. Motor noise: from magnetic-field vibration, cooling fans and so on. Structure-borne noise: car-body vibration travels through the structure, and onboard equipment adds to it. Aerodynamic noise: more pronounced as speed rises.
Matching controls
Use sound-absorbing materials and damping coatings inside the car body to absorb and remove noise; optimise the braking system and braking strategy; optimise motor design and reduce motor vibration; optimise the body structure, for example windows and doors, and reduce air-conditioning noise; optimise the body shape and cut air resistance to lower aerodynamic noise.
How to view the damping coating
A damping coating mainly deals with the vibration of body panels and the noise they radiate, and is only one part of the system scheme. Whether it fits has to be judged against the specific source, frequency and body construction.