I have noticed when out walking that the sound level of (say) distant motorway traffic or PA system is very significantly effected by my being upwind or downwind of the source. Bearing in mind that the wind speed might be as low as 10mph, and the speed of sound is over 700mph, I was wondering why this should be.
Sound waves are set of compressions and rarefactions travelling through space. The sound waves will be added vectorially to the direction of wind. In simple words if wind is in same direction as sound the net effect of sound waves will be greater, however if wind is in opposite direction to sound the net effect of sound waves will be diminished.
This is due to the refraction in the boundary layer of the wind above the ground.
Have a look here in the chapter "7b: Refraction":
Wave Behavior
Have a look here in the chapter "7b: Refraction":
Wave Behavior
The wind will shift phase for some frequencies more then other resulting in additional cancellation. Wind can also add some modulation effect like dobler effect.
Not only wind direction, but humidity as well.
I now live in the city, but for 40 years in the yard of my rural farm house, I could either hear quite clearly, or barely hear, the interstate highway two miles away or the railroad tracks five miles away. All depended on the weather.
I recall physics class, one of the problems we had to solve was determine the speed of an object by the Doppler shift in its sound. That is where your speed of sound factor comes in. The fact the sound pressure ripples have to fight to overcome a head wind is separate.
I now live in the city, but for 40 years in the yard of my rural farm house, I could either hear quite clearly, or barely hear, the interstate highway two miles away or the railroad tracks five miles away. All depended on the weather.
I recall physics class, one of the problems we had to solve was determine the speed of an object by the Doppler shift in its sound. That is where your speed of sound factor comes in. The fact the sound pressure ripples have to fight to overcome a head wind is separate.
Ton Danley notes outdoors PA systems are affected by wind, unless point source 🙂 Q&A: Tom Danley | audioXpress
" The concert systems that evolved for that market may be the best they know how to make, but they radiate an interference pattern you can hear if the wind blows. Every location has a different sound and radiate sound in the wrong directions. When you can eliminate all that interference, radiates enough acoustic power with one single source, and have more directivity, then it becomes a pretty obvious sonic choice. It’s as close to hi-fi as you can get on a grand scale.
The familiar large sound systems are a huge array of sources, which depend on DSP, and sound worse the larger they are. The Synergy horns work because the source is acoustically correct at the origin."
" The concert systems that evolved for that market may be the best they know how to make, but they radiate an interference pattern you can hear if the wind blows. Every location has a different sound and radiate sound in the wrong directions. When you can eliminate all that interference, radiates enough acoustic power with one single source, and have more directivity, then it becomes a pretty obvious sonic choice. It’s as close to hi-fi as you can get on a grand scale.
The familiar large sound systems are a huge array of sources, which depend on DSP, and sound worse the larger they are. The Synergy horns work because the source is acoustically correct at the origin."
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