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Outdoor Acoustics

Author: N.H. Crowhurst

Have you ever wondered why sound travels much better "downwind" than against the wind? With sound traveling at about 750 miles an hour, a wind of only a few miles an hour will obviously not be able to stop the sound, although the speed of sound relative to the ground does vary with the wind speed.

How the wind bends a train of sound waves.

The wind travels at different speeds at various heights above ground. Air in contact with the ground hardly moves at all, but the higher you go, the stronger the wind. For this reason, the higher part of the sound wave traveling with the wind moves faster than the part near the ground. (The wind speed is added to the normal speed of sound.) This makes the wave lean forward, and bear down on the ground, and the sound heard here is more intense than without the wind.

Traveling against the wind, sound at higher levels moves a little slower than on the ground, the wave leans back. It therefore "takes off" and does not carry to a listener on the ground.

Last Update: 2010-11-03