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Old 12-03-2013, 21:20   #1
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Doppler Effect or Not?

If you have a point source of sound, e.g. a fog horn, and the wind is coming toward you, will the sound be higher pitched as with the Doppler effect?

How 'bout if the wind is going away from you, will the sound be lower?
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Old 12-03-2013, 21:43   #2
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Quote:
Originally Posted by jongleur View Post
If you have a point source of sound, e.g. a fog horn, and the wind is coming toward you, will the sound be higher pitched as with the Doppler effect?

How 'bout if the wind is going away from you, will the sound be lower?
Yes of course. Just like an approaching train at a crossing. But from what I understand, the human ear cannot detect the shift if the speed of the medium (wind) or emitter (fog horn) or receiver (your body) is less than 2 knots relative of any one to the other
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Old 13-03-2013, 00:56   #3
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Re: Doppler Effect or Not?

Actually, I think that there will *not* be a Doppler shift if the sound source and your ears are in the same airstream. Depending on the wind direction, the sound will arrive sooner or later, but the frequency will be unaffected.

Interesting to think about the amount of shift for a particular speed difference. Sound travels about 768 MPH (667 Kts). The human ear/brain can typically detect a shift of 1/100 of an octave (2% frequency change). This gives us a "detectable" speed of 0.02 * 677 = 13 kts. I would have expected lower, so I wonder if my math (or assumptions) are off?

Here's a link to a sound clip of the Golden Gate Bridge foghorns: *
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Old 13-03-2013, 01:04   #4
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Re: Doppler Effect or Not?

No,..... it will be louder if the breeze is blowing from the fog horn to you and softer if the breeze is blowing from you towards the foghorn.
The Doppler effect only occurs when the source and the receiver are moving relative to each other...like the steam train coming towards you...pitch is higher...and away from you ...pitch is lower.
If the emitter and receiver are not moving relative to each other there is no Doppler effect.
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Old 13-03-2013, 02:22   #5
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Re: Doppler Effect or Not?

Interesting thought experiment

I'm with Alan, it's all relative. With the wind going towards the foghorn, as far as the wind is concerned the pitch goes up a bit, but as the wind is going away from the observer, between the observer and the wind the pitch goes back down by the same amount.

Now if it was a particularly breezy day with the wind moving at the speed of sound, would you ever hear the fog horn?
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Old 13-03-2013, 07:32   #6
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Re: Doppler Effect or Not?

AS far as the wind is concerned ...yes...if you the observer was moving with the wind...true...stationary observer, stationary foghorn...no

Again stationary observer, stationary foghorn....wind at speed of sound....coming towards you it would be deafening...going away from you...you wouldn't hear it
but the pitch wouldn't change...that only happens when the observer nd the foghorn are mving realtive to each other...nothing to do with the wind speed.
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Old 13-03-2013, 09:46   #7
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Re: Doppler Effect or Not?

Yes, I agree with Alan also. Simple little thought experiment.
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Old 13-03-2013, 10:20   #8
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Well, I agree with whomever agreed with physics. The relative speeds of the emitter, the medium, and the receiver contribute to the Doppler effect. The Doppler effect was first described by a Christian Doppler regarding to the change in the color spectrum of stars moving at different speeds relative to the earth. It was later applied to sound waves moving through air and water on earth by Ballot. Doppler effect is about pitch changing, not strength of signal. And whoever asked about if the speed was faster away from the observer than sound, would you ever hear it? No. And if the source or the medium is moving toward you at twice the speed of sound, you would eventually hear the sound (or music, or speech) backwards
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Old 13-03-2013, 10:43   #9
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Re: Doppler Effect or Not?

If you hear the music backwards at twice the speed of sound, doesn't that mean that if you travel twice the speed of light, you go backwards in time? Kind of flies in the face of the time dilation. Sorry for the thread drift but,many years ago, I spoke to a crowd of about 100,000 people. The crowd was so large, they had strung speakers about every 100 yards or so, so when I spoke, I heard my voice coming from each speaker delayed by a 10th of a second or so, until the last speaker, it was about a full half second before I heard my voice. I marveled at how long it took my voice to reach the last speaker, since I had always thought electronic sound traveled at the speed of light. It was a full day before I realized it was the time for the sound from the speaker to reach my ears, not the time for the signal to reach the speaker. (yes, I did feel pretty stupid)
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Old 14-03-2013, 14:58   #10
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Re: Doppler Effect or Not?

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If you hear the music backwards at twice the speed of sound, doesn't that mean that if you travel twice the speed of light, you go backwards in time? Kind of flies in the face of the time dilation. Sorry for the thread drift but,many years ago, I spoke to a crowd of about 100,000 people. The crowd was so large, they had strung speakers about every 100 yards or so, so when I spoke, I heard my voice coming from each speaker delayed by a 10th of a second or so, until the last speaker, it was about a full half second before I heard my voice. I marveled at how long it took my voice to reach the last speaker, since I had always thought electronic sound traveled at the speed of light. It was a full day before I realized it was the time for the sound from the speaker to reach my ears, not the time for the signal to reach the speaker. (yes, I did feel pretty stupid)
In some sound-reinforcement systems they actually put a delay in the mid and back-of-house speakers, so the sound from the speakers arrives at the audience at the same time as the sound from the stage. Of course the reflected sound that eventually gets back to the stage now has even *more* delay.

Once more, I think that as long as the source and the listener are stationary relative to each other, the pitch will not be affected regardless of the windspeed.

Think of this: On your boat, sailing with 30kts apparent wind, when the helmsman is shouting up to the bow, or vice versa, the voices don't sound doppler-shifted. I've been in an open-air railroad observation car, going pretty fast, and again no perceived doppler shift when yelling from one end of the car to the other.
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Old 14-03-2013, 15:13   #11
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Re: Doppler Effect or Not?

Doppler effect

Pronunciation: /ˈdɒplərɪfɛkt/


Definition of Doppler effect
noun


Physics
  • an increase (or decrease) in the frequency of sound, light, or other waves as the source and observer move towards (or away from) each other. The effect causes the sudden change in pitch noticeable in a passing siren, as well as the red shift seen by astronomers.
Oxford dictionary...anybody could have looked this up
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Old 14-03-2013, 15:53   #12
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Re: Doppler Effect or Not?

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Oxford dictionary...anybody could have looked this up
The definition of the Doppler effect was never in question. The question was whether sound being coupled into a moving medium also experiences a Doppler effect. While I think the answer is "no", the dictionary definition hardly precludes this possibility.
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Old 14-03-2013, 16:46   #13
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Re: Doppler Effect or Not?

Interesting .....I think the relative speed of the medium is a factor, the density of the medium is a bigger factor. Moving air is less dense (bernuli effect) relative to the same air when the wind settles down, so I think the pitch wound be lower in moving air, I dont think the direction of the movement is a factor except for the intensity of the sound. (assuming the air is the only thing moving)
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Old 14-03-2013, 17:00   #14
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Re: Doppler Effect or Not?

Think of this:

If the wind is moving from the point source towards the observer (listener), as the waves are generated, they are stretched out, appearing like a lower pitch. (longer waves = lower pitch, shorter waves = higher pitch). That's the first part of the effect.

Then, as the wind moves by the observer, the waves that have been stretched out, "hit" the observer faster with a shorter interval between them, because the wind is moving those waves faster, ergo, higher pitch, bringing the pitch back to how it was as generated.

Nicht var?
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Old 14-03-2013, 17:21   #15
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Re: Doppler Effect or Not?

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The definition of the Doppler effect was never in question. The question was whether sound being coupled into a moving medium also experiences a Doppler effect. While I think the answer is "no", the dictionary definition hardly precludes this possibility.
The answer IS NO !
The definition does preclude that possibility...the moving medium has no effect on pitch.
It is ONLY the relative motion of the source and receiver that produces the Doppler effect.....by definition...that is what the Doppler effect is.

And whatever you make like to "think"..that's it...no argument
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