Doppler Effect

[JimLucas]

Don't want to endanger my SoCC (Society of Confirmed Cynics) membership.

Is this the Society that gives, with each membership, a free subscription to either the Journal of Irreproducible Results, or the Annals of Improbable Research?

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Absolutely not! We wouldn't trust such publications!

 

In fact, we distrust even probable research and reproducible results.

[Chris Timson]

A chance, fair enough.  But not the benefit of the doubt.  I will continue to doubt until I see the result. 

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Sir, I demand satisfaction. I shall meet you at dawn tomorrow on Hackney Marshes. My seconds will call on you later today to discuss the choice of weaponry.

 

Lord St John Timson

[stuart estell]

The previous track record of the Last Word column (and it has been going for a few years now) is that most of the respondents would likely be professors of accoustics who, if they cannot come up with a ready reason, are likely to take it on as a research project. It's an impressive resource. You do the column and the magazine, and me come to that, a disservice.

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Agreed - and I think it was a great idea to write to NS. I look forward very much to any responses from its denizens.

Edited May 26, 2005 by stuart estell

[JimLucas]

Sir, I demand satisfaction. I shall meet you at dawn tomorrow on Hackney Marshes. My seconds will call on you later today to discuss the choice of weaponry.

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Seconds? Y'r gonna need weeks, maybe months.

Besides, my tomorrow morning is already booked.

 

Frankly, Chris, I hope that when they're finished you'll be able to say, "I told you so," and not me. But hope is a far as I'm willing to go until the results are in. Faith and charity are gonna have to wait.

 

Meanwhile, though, I should check the local library for copies of NS, and check out the colulmn.

[Stephen Mills]

I had a shufty at the Last Word portion of the New Scientist website. (Ha! Thanks to you, Chris, I’m the first native Texan ever to utter that initial phrase.) Some of the questions are a bit “out there”, e.g., What would happen to the world if the Earth were hollow below the crust? I hope your question is chosen, but I fear it doesn’t contain enough information. You were faced with some tough choices. As phrased, it is not entirely clear you believe the effect to be specific to, or at least most pronounced on the concertina. On the other hand, if you had made it concertina-specific, most readers would probably say, “Oh, well, I don’t know anything about concertinas.”

 

We’re a little short on hard evidence here. Let me posit some questions for you.

 

(1) I believe someone said concertina reeds were more affected than accordion reeds. Chris, you have both types and a baritone as well. Under what conditions is the effect most pronounced? Is there a specific frequency range where it’s worst?

 

(2) The question of orientation has not quite been addressed to my satisfaction. Chris, you could have Anne sit and play a series of notes on first the side facing the fan, then on the other side. On the English, the notes would thereby be about counterbalanced for pitch. You could also stand nearer the fan than she, and then further away. Does it make a difference? What is the effect of varying the distance you stand from Anne? What is the effect of varying the speed of the fan?

 

(3) Is the interference produced in the concertina, in the air, or in the ear? Some experiments: Record while producing the effect. Turn the fan off. Record the same playing without the fan. Play back the tape. Can you hear the effect on the tape? Can you produce the effect with a tape made without the fan, but played with the fan? This might help determine if the effect is produced by concertina-specific mechanisms or is a purely acoustic phenomenon. It is quite possible the effect might be specific to harmonic balances not reproduced accurately by the taping mechanism, however.

 

Another version of this would be to use headphones and a pickup on the concertina. If the effect is produced “at the concertina”, you should hear it. If the effect is produced as it is transmitted to you, you would not.

 

(4) Determine for sure that Anne’s violin does not produce the effect. Whistle and harmonica data would be useful. Got any brass or wind instruments lying around?

 

(5) Of course, now that you’ve got the recording, get Danny Chapman to do wavelet or Fourier analysis on recordings with and without the fan running.

 

More work than you had in mind? Also, I make no claim I can interpret the evidence were you to collect it.

Edited May 26, 2005 by Stephen Mills

[Chris Timson]

More work than you had in mind? 

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Definitely! However there are a number of interesting suggestions with real merit here. Perhaps after this weekend (which is a public holiday here as I gather it is in the States) we can parcel up the experiments among a few volunteers and report back our results. In other words, a sort of reverse Goran.

 

Chris

[John Wild]

[sir, I demand satisfaction. I shall meet you at dawn tomorrow on Hackney Marshes. My seconds will call on you later today to discuss the choice of weaponry.

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Please forgive me sidetracking from the main topic, but this reminded me of a folk club performer some years ago, who, in a response to an audience heckler said:-

 

"I've got a soft spot for hecklers - it's in the middle of the Hackney Marshes"

 

I've heard similar responses several times quoting Romney Marshes and the Goodwin Sands. I expect equivalent examples exist in other areas.

 

 

- John Wild

[Robin Madge]

I just remembered some possibly relevant information on the "Doppler effect" front.

 

I once recorded myself "doing the bells" using a fixed position microphone about 8 feet in front of me. I could hear the Dopler effect quite clearly.

 

I repeated the recording using Microvox microphones attached to the ends of the concertina. I could still hear the effect.

 

How does that work?

 

Robin Madge

[David Barnert]

I just remembered some possibly relevant information on the "Doppler effect" front.

 

I once recorded myself "doing the bells" using a fixed position microphone about 8 feet in front of me. I could hear the Dopler effect quite clearly.

 

I repeated the recording using Microvox microphones attached to the ends of the concertina. I could still hear the effect.

 

How does that work?

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Are you sure that what you heard was actually a doppler effect? Describe what you heard. If it was the wobbly tone we have been discussing here, it is by no means agreed that doppler has anything to do with it.

[Robin Madge]

The closest thing I can think of is the sound that you get if you amplify a concertina and put the signal through a phaser or digital delay pedal ( I've done both!).

 

Robin Madge

[David Barnert]

The closest thing I can think of is the sound that you get if you amplify a concertina and put the signal through a phaser or digital delay pedal ( I've done both!).

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I haven't done either, but I'd be surprised if what came out was a "Dopler effect," which most folks would use to describe the sound of an approaching train whistle or siren dropping in pitch as it passes and recedes into the distance. If that's not what you're hearing, then calling it a doppler effect doesn't make it one.

[A.D. Homan]

[...] a "Dop[p]ler effect," which most folks would use to describe the sound of an approaching train whistle or siren dropping in pitch as it passes and recedes into the distance. If that's not what you're hearing, then calling it a doppler effect doesn't make it one.

 

But it might make it many, rather than one.

 

I've discussed this again with a friend who is a physicist. I brought up the argument against it being the Doppler effect. Here's a summary of his explanation: He said that it's true that the basic description of the phenomenon is that the pitch seems to drop as the source moves away from the listener. In the case of the musical instrument playing near a fan, we have to think about the fan blades as "sources" of _many_ reflections of the sound. The distance to the listener constantly oscillates. These pitches in turn interfere with the pitches originating from the instrument.

 

So no, it is not one doppler effect, but MANY. And on top of that, there is certainly also interference (hence the "wet tuning" effect).

 

The physicist, by the way, is a fiddler, and he reported experiencing it while playing the fiddle. I've also noticed it -- faintly -- this last week while playing an openback banjo in a room with a ceiling fan.

 

With cooler weather on the way, I expect the topic will go away until next summer...

[JimLucas]

[...] a "Dop[p]ler effect," which most folks would use to describe the sound of an approaching train whistle or siren dropping in pitch as it passes and recedes into the distance. If that's not what you're hearing, then calling it a doppler effect doesn't make it one.

But it might make it many, rather than one.

"Might" isn't the same as "does".

 

I've discussed this again with a friend who is a physicist.  I brought up the argument against it being the Doppler effect.  Here's a summary of his explanation: He said that it's true that the basic description of the phenomenon is that the pitch seems to drop as the source moves away from the listener.  In the case of the musical instrument playing near a fan, we have to think about the fan blades as "sources" of _many_ reflections of the sound.  The distance to the listener constantly oscillates.  These pitches in turn interfere with the pitches originating from the instrument.

While there may indeed be some Doppler effect(s), I question whether it's strong enough to be the full explanation of the observed fan effect. How large a pitch difference would be needed to be noticeable? How far and fast would it be necessary to move the fan blades (or the concertina) to achieve that pitch difference (or range of differences)?

 

I compute that the difference in wavelength between A440 and 10 cents less is a little under 5 mm, or about 2 meters of distance in a second. If we consider a "forward-back" motion of 4 inches (is that reasonable for the difference between near and far edges of a fan blade?), that would require oscillation at 20 times per second, or about 8 times the 10-cent frequency differece postulated as a cause of what we hear. If we only need a 1-cent difference, then we may be approaching the same ballpark, but I have doubts about that being enough.

 

So no, it is not one doppler effect, but MANY.

Perhaps "there is", but not "it is". There are certainly other factors (see next).

 

And on top of that, there is certainly also interference (hence the "wet tuning" effect).

If there are multiple pitches close together, there will be interference, but there will also be spatial interference -- what you see with diffraction gratings -- of the reflections from the multiple fan blades, and various walls if you're in a room.

 

The effect of the walls, by the way, is quite noticeable... we call it "acoustics". There can be considerable variation in the sound, depending on where the instrument and the listener are placed. But we don't notice it as a "wobbly" sound, because the walls don't usually move. (Has anybody noticed the "fan" effect in a fanless room when they themselves have been wobbly drunk? )

 

With cooler weather on the way, I expect the topic will go away until next summer...

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I've been thinking of producing an extended analysis for release around Christmas time.

 

I once recorded myself "doing the bells" using a fixed position microphone about 8 feet in front of me. I could hear the [not-Doppler] effect quite clearly.

I repeated the recording using Microvox microphones attached to the ends of the concertina. I could still hear the effect.

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An excellent question, but you seem to have demonstrated that the effect of "the bells" is definitely not a Doppler effect, because the microphones were always the same distance from the sound source. Whether what causes the "bells" effect is also a factor in the "fan" effect remains to be determined.

[A.D. Homan]

[...] a "Dop[p]ler effect," which most folks would use to describe the sound of an approaching train whistle or siren dropping in pitch as it passes and recedes into the distance. If that's not what you're hearing, then calling it a doppler effect doesn't make it one.

But it might make it many, rather than one.

"Might" isn't the same as "does".

 

It is not clear why you would pick at this language, Jim, other that to demonstrate the j*ck*$$ effect, which isn't the topic here.

 

I chose to say "might" because I'm relating someone else's explanation as a possibility, rather than asserting it as a fact that I have concluded on my own. I do believe that it is the correct explanation, and I respect the source from which it came (a physicist whose research field is physics of sound). I look forward to your extended analysis since I find amateur science amusing -- I've been wrong often enough about these matters to have concluded that I should always check first with someone who is more than an armchair scientist! Who knows, you "might" be correct.

 

Edited to insert the correct code for "end quote."

Edited to add mild self-deprecation.

Edited August 23, 2005 by A.D. Homan

[tony]

 

It is not clear why you would pick at this language, Jim, other that to demonstrate the j*ck*$$ effect, which isn't the topic here.

 

I chose to say "might" because I'm relating someone else's explanation as a possibility, rather than asserting it as a fact that I have concluded on my own. I do believe that it is the correct explanation, and I respect the source from which it came (a physicist whose research field is physics of sound). I look forward to your extended analysis since I find amateur science amusing! Who knows, you "might" be correct.

 

Edited to insert the correct code for "end quote."

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Well said.

Edited August 23, 2005 by tony

[JimLucas]

[...] a "Dop[p]ler effect," which most folks would use to describe the sound of an approaching train whistle or siren dropping in pitch as it passes and recedes into the distance. If that's not what you're hearing, then calling it a doppler effect doesn't make it one.

But it might make it many, rather than one.

"Might" isn't the same as "does".

It is not clear why you would pick at this language, Jim, other that to demonstrate the j*ck*$$ effect, which isn't the topic here.

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A.D., I don't know what you mean by the jackass effect (I can think of various possibilities), but I'll try to make my purpose clear:

 

Further down in your same post, you said:

So no, it is not one doppler effect, but MANY.

I cannot consider your two statements to be independent. Thus I felt it important to emphasize the uncertainty of the "might" in the first statement, an uncertainty that was explicitly denied in the second statement.

 

Furthermore, David's statement didn't agree that the Doppler effect was involved and debate the number of times. He was questioning the claim that it was "Doppler" at all. But by quoting him and making your statement as a response to his, you implied that you were arguing against what he said, i.e, that the word "might" -- which equals "might not", though that equality is often overlooked -- wasn't intended to mean "might not be Doppler", but only "might not be just one". I felt that this also warranted highlighting the uncertainty of the word "might".

[A.D. Homan]

[i cannot consider your two statements to be independent.  Thus I felt it important to emphasize the uncertainty of the "might" in the first statement, an uncertainty that was explicitly denied in the second statement.

 

The first statement was my own statement, the second is a paraphrase of my friend's explanation. The first statement is just a transition, playing with Dave's statement. The second is an explanation of the observed effect, in opposition to the opinion that the Doppler effect is not involved.

 

I feel that you are picking at secondary language rather than facing the topic at hand, which is an attempt to explain the effect. I appreciate your post on the other recent thread. Personally, I feel that we are observed multiple effects, and that we haven't parsed them enough to really get to the heart of the matter. I am also not satisfied with the explanation that it is "ONLY" Doppler. Nor am I content to accept the explanations of why it seems to effect certain instruments more than others.

 

It's nice if the discussion would continue; it's not nice when opposing views are simply picked apart because they were quickly written, or when someone treats the topic as tiresome or "case closed." From my point of view, I've received a reasonable explanation from someone who can claim some authority on the matter, so I'm taking that explanation as being "standard"; I respect that physicists disagree on the topic. So it seems odd to me that this one explanation is so quickly discarded so uncharitably in favor of anectdotal ponderings, some of which contradict each other to begin with. (Such as the case where one poster at one time DID observe the effect -- in 2000 -- with hammer dulcimer, and at another time did NOT observe the effect -- in 2005.)

 

I also find it unfortunate that several of your posts, Jim and Chris -- intentionally or not -- contain rhetorical attempts to belittle the source of my information. I found it appropriate to contribute to the discussion by passing on explanations that had been given to me by someone who happens to teach and research in this field, happens to have his PhD. in physics, and happens to be a fiddler who has observed this effect from the fan at a local session! Maybe I'm being overly-sensitive, but I find it belittling to refer to him as "your teacher," or to make it seem that he has contradicted the standard explanations on the matter, as Chris did so sarcastically in the other thread. Excuse me for seeking a reasonable and informed response to these threads and attempting to relay the information in what I've always assumed to be a discussion among more than just a fraternity of men who have written thousands of posts on this forum!

Edited August 25, 2005 by A.D. Homan

[David Barnert]

OK, I've done a little impromptu experimenting, and while I wasn't able to do all the experiments I previously envisioned, what I was able to do convinced me more than ever that my original guess was correct and the Doppler effect has *nothing* to do with the fan effect.

 

There was a standing (pedestal?) fan, about 18 inches across and 4 feet off the floor at Morris Dance practice this evening. I had with me my concertina and a low F tabor pipe. No digital recorders.

 

I stood facing of the fan at a distance of two feet and played the low note (F above middle C) on my pipe (case A). No distortion. Nice smooth tone. Then I played the same F on the concertina (case . The sound was very choppy, the classic fan effect, and I distinctly heard it from the direction of the concertina, not the fan. Then I turned my back on the fan and held the concertina in front of me, hidden from the fan by my torso. I played the note again, louder, loud enough to be heard behind me, at the fan (case C). No distortion.

 

I can see no other interpretation of these results but the following:

 

There are sound waves traveling from concertina to fan, from concertina to ear, and from fan to ear (waves traveling other routes are not relevant to this discussion). The "Doppler" explanation can only be valid if the fan effect has its action on the waves that travel from fan to ear.

 

But if the action of the fan effect were happening between fan and ear, it would have the same effect on the concertina sound in cases B and C. It would also act in case A, the tabor pipe. Ergo, no Doppler effect. The sound waves traveling from concertina to fan (and to ear) are already distorted, and only when I don't stand between concertina and fan.

 

Whatever is happening is happening at the location of the sound production (the reeds) and must rely on the presence of the air pressure effects of the fan, unimpeded by my rather substantial midsection.

 

It is still only at the guess level on my part that the explanation is that rapidly varying air pressure at the reeds is causing rapid changes in pitch, but other explanations are disappearing quickly.

 

I refer back to my comments at this post, including my thoughts from five years ago, which have not changed:

I'm not so sure it's a Doppler effect. If so, why does it only seem to happen with free reeds? My guess is that the spinning fan blades create rapidly alternating puffs of relatively higher and lower air pressure at the location of the vibrating reed, causing periodic variations in the frequency of its vibrations.

A.D., please show this to your physicist friend for comment.

 

 

When you have eliminated the impossible, Watson, what remains, however improbable, must be the truth.

 

Edited for: Oh, hell, this kind of stuff never comes out right the first time. I added a few words that were in the first draft and accidentally got edited out of the one I originally posted.

Edited September 15, 2005 by David Barnert