Structure-borne noise of urban rail vehicles: sources, frequency distribution and control
Structure-borne noise is vibration that travels through the car-body structure and is then radiated as noise; it is a key part of urban rail vehicle noise.
Where the noise comes from
Vibration from wheel–rail contact travels through the vehicle structure; vibration from onboard equipment such as air conditioning and motors travels through it too; and the vibration of structures such as wall panels and floors produces noise as well.
Frequency distribution
The distribution is wide: low-frequency wheel–rail vibration noise at 20–200 Hz as well as high-frequency equipment noise at 1–5 kHz. The frequency of wheel–rail noise depends on speed and track condition, and that of equipment noise on how the equipment runs.
Control approach
Wheel–rail vibration: optimise the contact conditions, for example with good wheel and rail materials and improved design, to reduce vibration at the source; use damping materials such as water-based damping coatings to reduce its spread. Equipment noise: optimise equipment design to cut running vibration, and add damping material to existing equipment. Vehicle structure: optimise the design, raise stiffness and damping, and add damping material to reduce vibration spread.