Trains actually don't make that sound. The rails make it. A rail is not a single metal piece but a series of rail pieces with certain length. ... The sound is generated because of the lateral movement of the wheels and subsequent connection/friction with the tracks.
Train noise is vehicle noise created by trains. Noises may be heard inside the train and outside. Various parts of a train produce noise, and different kinds of train wheels produce different amounts of noise. Noise barriers can attenuate the noise.
Subways, Light Rail transit and freight trains can send loud train noise into neighborhoods. Organizations such as the World Health Organization and the U.S. Environmental Protection Agency have set guidelines for noise level decibel limits for Rapid Transit
Train noise can be a type of environmental noise. When a train is moving, there are several distinct sounds such as the locomotive engine noise and the wheels turning on the railroad track. The air displacement of a train or subway car in a tunnel can create different whooshing sounds.
Trains also employ horns, whistles, bells, and other noisemaking devices for both communication and warning.
Trains propelled by electric traction motors often produce electromagnetically-excited noise. This high pitch noise depends on the speed and torque level of the machine, as well as on the motor type. Variable frequency drives use Pulse-width modulation technique which introduces additional current harmonics, resulting in higher acoustic noise. The switching frequency of the PWM can be asynchronous (independent of the speed), synchronous (proportional to the speed), but always results in acoustic noise varying with speed.
Flange Squeal is the sound of the flanges of the metal train wheelset turning on the train track.
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