Frequency/Penetrating power ???

[YT2095]

the speed of sound at sea level and whatever temp is known and has a number or a constant.

 

sound uses air as the medium in my example, I want to know Why you can hear a sound some distance away when the wind is blowing the air across the path of that sound?

 

how come I can still hear across several rooms when there is a Fan blowing across the path, it even works if you use a cardboard tube to listen through.

 

since air is the carrier, surely the sound should stop if that air that`s carrying that sound is moved away by an airflow, and yet it isn`t!?

 

what`s going on?

[iNow]

First guess? The pressure wave travelling through the air is significantly faster than the fan or wind, so the effect of these aren't noteworthy. Perhaps the sound is somewhat redshifted, but I can't believe a box fan would be strong enough to push back all of the bouncing molecules being carried by that pressure wave at roughly 340 m/s.

 

Also, the fan and/or wind are not creating a vacuum, so while some air is displaced there is still more than enough to transmit the pressure wave of sound.

 

 

This is just a guess though.

[YT2095]

Thnx, 340m/s is great!

 

so I stand 340m away from you on a beach, the wind is blowing at 10m/s across our sound path, you shout at me, should I be able to hear you, or will the sound be 10 metres to one side of me?

and will this change if you use a High frequency or a Low frequency?

[insane_alien]

the sound would be 10m to the side only if you used the sonic equivalent of a laser to broadcast the sound.

 

fortunately we broadcast in all directions so accuracy isn't so much of an issue.

[YT2095]

well yes, and I agree, but why do some sound frequencies travel better than others under the same conditions?

[swansont]

I'm guessing the response of the atoms isn't a constant over all frequencies. Different absorption rates and possibly having speed depending on frequency (dispersion) or not.

[YT2095]

I wondered if it was like Photon behavior, VLF and ELF will penetrate almost anything, as will Gamma and yet microwaves are easily stopped as is UHF or and top end VHF as well as Light etc...

to my understanding a Photon is a Photon and that`s that, and yet alter the frequency and you get different behaviors for penetrating power.

 

could Sound work in a similar way?

[swansont]

For photons, materials have certain frequencies where they absorb. For sound, I can imagine that different atoms respond better or worse to the vibrations, depending on their mass and the mass of things around them. And there could also be resonances where the energy at one frequency is absorbed and down-converted more or less efficiently, resulting in loss.

[Externet]

A similar case would be

 

Would a stone thrown on a river make waves that will reach the shore anyway even when the current is transporting the water mass down the river?

[insane_alien]

well as long as the current of the water isn't 'supersonic' for the surface waves. if the winds are over 330m·s^-1 round YT's bit then he has a bit more to worry about than whether the guy across the street can hear him.

[alan2here]

What a kick-ass example Externet.

 

Observation:

We tend to look at all frequency's of EM waves and only the very lowest of the sound wave frequency's.

[YT2095]

I`m happy with either scenario, both address my question equally well.

[Externet]

Alan - Not here to kick any ass, and less YT's . Am here to learn.

 

Just another point of view perhaps more visualizable than audio and air. If the waves reach the stone thrower's shore, should explain the independence between both medium and wave propagations. YT's question is a good valid one, and electromagnetic waves and mechanical waves do not behave equal.

Miguel

[Rocket Man]

ever watched a jet fly over head and listened for it's location? it sounds way behind the point you see it.

standing on a beach with a cross wind, the sound seems to come from down wind. from yt's example, the sound appears to come from roughly 10m downwind of the speaker

[Externet]

A sound wave propagates at 340 m/s ; air from a fan across may move at say 3.4 m/s for easy figures. We have 100:1 ratio.

 

A wavefront from a stone thrown on a river may propagate at about 50 cm/s ; for the same ratio of 100:1 would mean the current flowing at 5 mm/s -relatively very slow - With such speeds, is easy to visualize the wave will reach the shore in front of the thrower in good intensity.

 

Perhaps that (ratio) is why the sound does make it across the crosswind. If the river was much, much faster, as 1m/s , the wave would not reach the shore in front of the thrower, but way down the river. (equivalent of sound not being heard) Seems a fast enough air speed would prevent hearing the sound. Just trying to find an explanation.

 

Miguel

[iNow]

Seems a fast enough air speed would prevent hearing the sound.

Sound is, in simple terms, a vibration. Air speed plays a role, in that it displaces the medium through which sound propogates, but really something must "absorb" the sound (dissipate it's vibration) in order to prevent it from being heard.