Does the wind 'blow' sound?

[rix]

Often heard it said that you can hear different things depending on what way the wind is blowing, and I guess I've blindly accepted it, however is there any truth or science behind it?

If not, why is it that some days the M11, probably a 1/4 mile from my house is quite noisey, where as at others I can't hear it at all?!

[jmorgan]

Sound needs to get to your ear to vibrate the doings inside your skull via the diaphragm. The air vibrations generated in air need to move from the source to you ear 'ole. If the wind is blowing against that sound wave then it will sound different to if it is coming in with the wind.

Tis the way I have always thought of it if that makes sense and is in any way correct?

[DoubleSix]

When the air/wind is still, sound will travel much further. Sound will also be disrupted by wind etc

Had some very still days recently and you could clearly hear kids playing on the school fields some distance away which you never normally can.

[Eric Mc]

Since sound is generated in air, of course wind direction and other atmospheric conditions will have a major effect on how sound travels.

[MartG]

layers of air at different temperatures can refract soundwaves, making them act in odd ways - e.g. under the right conditions a road may sound quiet 100m from it but noisy twice as far away

[Nightmare]

Eric Mc said:

Since sound is generated in air, of course wind direction and other atmospheric conditions will have a major effect on how sound travels.

hardly answering the question though! Wind does NOT blow sounds waves anywhere...the air will, as other people have said, interact with it in a number of ways, but you couldn't direct a sound somewhere by putting a fan behind it if you wanted to.....

[Hooli]

Nightmare said:

Eric Mc said:

Since sound is generated in air, of course wind direction and other atmospheric conditions will have a major effect on how sound travels.

hardly answering the question though! Wind does NOT blow sounds waves anywhere...the air will, as other people have said, interact with it in a number of ways, but you couldn't direct a sound somewhere by putting a fan behind it if you wanted to.....

Surely you can, slightly.

If I understand it correctly then sound travels faster over the ground downwind as it's doing the speed of sound + windspeed.

[rix]

Although, I guess, relative to the speed of sound a 60mph gust isn't going to make a perceptible difference!

[Mr2Mike]

Nightmare said:

hardly answering the question though! Wind does NOT blow sounds waves anywhere...the air will, as other people have said, interact with it in a number of ways, but you couldn't direct a sound somewhere by putting a fan behind it if you wanted to.....

You can't "blow" the sound along, but the boundary between fast and slow moving air will refract sound so it can travel further if the conditions are correct.

[Simpo Two]

Wind certainly affects sound. The traffic noise from the main road near my boat travels much further downwind than upwind, maybe by a factor of 5.

If sound is not 'blown' by the wind then it must be attenuating it somehow.

[Flibble]

rix said:

Although, I guess, relative to the speed of sound a 60mph gust isn't going to make a perceptible difference!

The speed of sound is around 760 mph (depending on temperature) so 60 mph is a fair proportion of that. You can hear the Doppler effect on cars travelling at those sorts of speeds so I don't see why a gust of wind wouldn't be able to affect it.

[Simpo Two]

Of course... a 760mph chunk of sound travelling into a 60mph headwind only does 700mph groundspeed!

And so maybe because it goes slower, it attentuates en route so that by the time it gets there it's proportionately quieter...?

[annodomini2]

Flibble said:

rix said:

Although, I guess, relative to the speed of sound a 60mph gust isn't going to make a perceptible difference!

The speed of sound is around 760 mph (depending on temperature) so 60 mph is a fair proportion of that. You can hear the Doppler effect on cars travelling at those sorts of speeds so I don't see why a gust of wind wouldn't be able to affect it.

And air pressure.

Speed of sound @ 30,000' is ~678mph, as the air pressure is rougly 30 kPa, vs 101 at sea level.

[Flibble]

annodomini2 said:

And air pressure.

Speed of sound @ 30,000' is ~678mph, as the air pressure is rougly 30 kPa, vs 101 at sea level.

Apparently not: http://en.wikipedia.org/wiki/Speed_of_sound#Detail...

The changes in speed of sound with altitude are from the temperature difference, not pressure.

[jmorgan]

I would have thought air temperature does have a relation to pressure?

[Flibble]

jmorgan said:

I would have thought air temperature does have a relation to pressure?

In an enclosed space, yes, in the atmosphere, not really.

[annodomini2]

Flibble said:

annodomini2 said:

And air pressure.

Speed of sound @ 30,000' is ~678mph, as the air pressure is rougly 30 kPa, vs 101 at sea level.

Apparently not: http://en.wikipedia.org/wiki/Speed_of_sound#Detail...

The changes in speed of sound with altitude are from the temperature difference, not pressure.

Interesting:

Wikipedia said:

In fact, assuming an ideal gas, the speed of sound c depends on temperature only, not on the pressure or density (since these change in lockstep for a given temperature and cancel out). Air is almost an ideal gas. The temperature of the air varies with altitude, giving the following variations in the speed of sound using the standard atmosphere - actual conditions may vary.

I'm curious how this has been verified and how the statement that the pressure at altitude is purely a function of temperature and is, according to this statement, never the other way around?

I may be wrong, but sounds very like an assumption to simplify the maths rather than empirical fact.

In fact, elements I've read elsewhere would probably contradict this and I'd like to see experimental evidence of the speed of sound being measured with the relevant lower temperatures but higher atmospheric pressures.

I can understand the medium being in a lower energy state at a lower temperature, which may increase the effective resistance of the sound wave to travel, but density of the medium will also affect this, the writer, imo is assuming that the pressure and density are a function of this temperature, which to me doesn't appear logical.

Like I said, I'm no expert and may be wrong, but I'm still sceptical of that statement.

[timbob]

The wind definitely makes a difference. My house is approximately 300 meters from the local church. On a still Friday when they do bell ringing practice you can hear the bells crystal clear. If the wind is swirling, the sound will alternate quite audibly with the gusts. Sometimes you can hear the bells really quite loudly (louder than normal perhaps?), but then the sound will all but disappear completely.

[SpeckledJim]

Simpo Two said:

Of course... a 760mph chunk of sound travelling into a 60mph headwind only does 700mph groundspeed!

And so maybe because it goes slower, it attentuates en route so that by the time it gets there it's proportionately quieter...?

It's proportionately quieter because it has, in effect, had further to travel. If you imagine the sound as a runner, and the air as a travellator, it either helps or hinders progress, at constant running speed.

[Simpo Two]

Bingo.