Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: paul.fr on 04/05/2007 23:28:17

Title: Shouting in the wind.
Post by: paul.fr on 04/05/2007 23:28:17

If one shouts into a strong wind, does the sound carry farther?

Title: Shouting in the wind.
Post by: another_someone on 04/05/2007 23:40:29

I assume when you are talking about shouting 'into' a wind, you actually mean shouting downwind, not the usual meaning of the term, which is to shout upwind.

It depends on what you mean by the sound carrying further.

The sound itself may well carry further, is a very narrow sense (although, in reality, the sound anyway carries out to infinity), but the problem is not the sound, but the level of noise (how much of the sound you can hear over the ambient noise), and I would suspect that a strong wind would create much higher noise levels that would more than offset the effect of the sound travelling further.

Title: Shouting in the wind.
Post by: paul.fr on 04/05/2007 23:47:08

Ok, lets say when i shout to a friend he can hear me 200m away, but not at 250m. If i then shout into a wind that is blowing from my direction towards my friends would he now be able to hear me 250m away?

Title: Shouting in the wind.
Post by: daveshorts on 05/05/2007 01:00:58

If there is no wind the sound waves will radiate in circles (technically spheres)  around the source (you) like ripples on a pond. If the wind is blowing then it is a bit like throwing a stone into a moving river, the circular ripples will move with the river / wind. So if there are no issues with noise produced by the wind, your voice should be louder 50m downwind than 50m upwind.

Title: Shouting in the wind.
Post by: Batroost on 05/05/2007 11:27:06

Quote

(although, in reality, the sound anyway carries out to infinity),

Well, until the sound vibrations are no larger than the (thermal) energies of the gas molecules, anyway. There ought to be a standard model for this?

Quote

Ok, lets say when i shout to a friend he can hear me 200m away, but not at 250m. If i then shout into a wind that is blowing from my direction towards my friends would he now be able to hear me 250m away?

The other effect you'd be able to measure is that the frequency of the sound your friend would hear would be slightly lower than the sound you'd made. This is beacuse the moving air into which you are shouting would stretch-out the sound waves slightly.

Title: Shouting in the wind.
Post by: lightarrow on 06/05/2007 22:31:54

Quote from: daveshorts on 05/05/2007 01:00:58

If there is no wind the sound waves will radiate in circles (technically spheres)  around the source (you) like ripples on a pond. If the wind is blowing then it is a bit like throwing a stone into a moving river, the circular ripples will move with the river / wind. So if there are no issues with noise produced by the wind, your voice should be louder 50m downwind than 50m upwind.

Yes, the source intensity is higher in the direction and versus of the wind. In simple terms: if there is no wind, after 1 second all the energy of a short sound pulse is spread on a sphere around you with radius 340 metres. If there is a wind with speed v towards right, after 1 second that energy is shifted to the right, with respect to the sphere of the first case.
The sphere has became an "elongated sphere" shape, so there is more energy in that solid angle --> larger intensity.