Why does a train sound different as it approaches or on the railway bridge?

Question

Why does a train sound different as it approaches or on the railway bridge?

Answer 1

Heinz and Pres. Eisenhower are absolutely correct if your question is about the sound of the whistle.

As far as the associated rumble present with a moving freight train passing by, when on a trestle the sound waves propagate into thin air.  The distance the sound waves travel through the air drops off exponentially as the distance from the source increases.  This is expressed in a formula known as the "inverse square."  Audio engineers who regularly work with outdoor sound systems are quite familiar with it.

This is another reason for pedestrians to stay off of railroad bridges and trestles.  A train can sneak up on a person.  The same thing happens when there is deep snow on the ground, the snow sucking up sound waves like a very efficient sponge.

So, stay off the tracks and stay alive.

Answer 2

Sound wave refraction...if the surroundings change so will the volume of the noise

D

www.stockmysite.com

Answer 3

Doppler effect.  Due to changing speeds between the train's horn and the observer, the frequency of the sound changes.

In answer to your email:

Slowing to a stop there is a change in speed between the train and you and that change in speed also changes the sound

Answer 4

beats me same horn