Why does Sound Travel Better with the Wind?
In very basic terms, the velocity at which sound moves is only slightly affected by the speed of the wind. A key to understanding how moving air affects sound lies in the word “moderate.” Many of us have had the experience of hearing sounds created at long distances if the air is still and cool. These sounds will travel at about the same speed and over the same distance if the air is moving at a moderate speed.
First, let’s look at a couple of definitions of sound waves, so we know what we’re listening for. According to Wikipedia, “Sound is a travelling wave which is an oscillation of pressure transmitted through a solid, liquid, or gas, composed of frequencies within the range of hearing and of a level sufficiently strong to be heard, or the sensation stimulated in organs of hearing by such vibrations.”
The Web site, physicsclassroom.com defines it this way: “Sound is a mechanical wave which results from the back and forth vibration of the particles of the medium through which the sound wave is moving. If a sound wave is moving from left to right through air, then particles of air will be displaced both rightward and leftward as the energy of the sound wave passes through it. The motion of the particles is parallel (and anti-parallel) to the direction of the energy transport. This is what characterizes sound waves in air as longitudinal waves.”
General belief holds that we can hear sounds better if they come “downwind,” which means the sounds are coming from the same direction as the wind is blowing. There is not a lot of evidence that the wind actually helps the sound along. As we mentioned earlier, the helping strength of the moving air we know as wind is not really enough to make a significant difference.
Sound moves through our air at about 760 miles-per-hour. A slight breeze from the same direction as the sound would be so small in relation to this speed that it has little effect. We should also consider that if the wind is really blowing, perhaps at a speed of 40 miles per hour or stronger, this is still just a fraction of the speed of sound. Human ears probably won’t be able to detect a difference in how quickly the sound arrives.
Many scientific studies and academic texts introduce another idea to help us understand how sound moves through air. Near the Earth there is turbulence that can prevent waves of sound from moving as quickly and efficiently as it would in completely still conditions. Sound moving against the wind is often forced up and away from our ears, with the opposite being true when the sound is moving with the wind.
For our purposes, sound moves in waves that can be affected by more significant turbulence in the air. In addition, our ability to hear sounds will be affected by the turbulence around our ears.