On Wed, 17 Jun 2009 10:12:09 +0100, Joe Egginton
wrote:

Weatherlawyer wrote:
On Jun 17, 12:55 am, "jbm" wrote:
The movement of the trains continually drags in air from outside. Stand
on any platform, and you can feel the movement of air as the trains approach
and recede.

I wonder how the air dynamics of trains has been analysed for the
effect it has on acoustics. The sound of an approaching train vss the
sound of a receding one give credence to the theories about red and
blue shift.

I imagine the vortex tunnels that they form in passing at speed in
excess of 60 mph would trap sounds of some frequencies while the
tunnels last.

Might that be why the louder, deeper sounds persist so long after the
passing of a train? That one has always puzzled me.

The maximum speed of undergound trains is 20mph.

About 40-50MPH in the tube tunnels.


--
Regards, Paul Herber, Sandrila Ltd. http://www.sandrila.co.uk/