Track vibration noise of urban rail vehicles: frequency distribution and control
Track vibration noise comes mainly from vibration at the wheel–rail contact and is broadband noise. The frequency distribution has to be understood before it can be treated properly.
Frequency distribution
The noise runs from 20–200 Hz in the low band up to 1–3 kHz in the high band; the exact distribution varies with running speed and track condition.
Where each band comes from
Low band: vibration caused by wheel and rail roughness and by centrifugal force on the wheelset in curves, strongly felt by people. Mid band (200–1000 Hz): elastic vibration of the track and wheelset vibration, strongly affected by speed and track condition. High band: high-frequency vibration at the wheel–rail contact and impact noise at switches and crossings.
Control approach
Low band: optimise vehicle and track design, use better wheelset materials, improve track maintenance. Mid band: raise track stiffness, use damping materials and optimise running strategy; a water-based damping coating with good damping can help lower mid-band noise. High band: optimise speed through switches and crossings, improve track condition and use noise barriers.