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#81
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"Ben Bradley" wrote in message news On Mon, 16 Aug 2004 21:57:16 -0500, "Porky" wrote: "PenguiN" wrote in message . com... If you still don't believe that this scenario validates the train-whistle analogy, why not make the bass waveform move at the speed of, oh say a train, and have the high pitched signal on top of it be, oh say the sound of a whistle. Doesn't apply, the train and whistle are supplied by two separate sources of energy. Have two amplifiers, one for the low frequency connected to the speaker through an inductor, another amp outputting the high frequency connected to the speaker through a capacitor. Thus the low and the high are supplied by two separate sources of energy. Actually, isn't the train whistle powered by steam from the same boiler that powers the wheels, moving the train? What's up with that? But seriously, for Bob and other anti-doppler-distortion folks, how does cone-and-frame movement cause doppler while cone movement only does not? What is it about the frame that causes doppler? If you put the speaker on a shaker table, run 1kHz and 50 Hz through the speaker, move the shaker table at 50 Hz opposite the phase to the speaker so the cone only moves at the 1kHz rate with respect to the air, will it generate doppler distorion? According to my understanding of Bob's position, it should. The whole thing hinges on the single complex waveform vs multile simple waveform idea. If the two sound signals are mixed into a single complex signal and that signal is what drives the cone, there are not actually two discrete signals being converted to sound, there is a single complex signal that our ears interpret as two different sounds. This isn't an exact anology either, but it's better than the train/whistle thing. If you play a CD of an orchestral performance, there is not one piece of analytic equipment man has ever designed or built that can completely separate and isolate the individual instruments, but any human with decent hearing and a bit of training can. This would seem to support the argument that the speaker is producing a complex waveform as a whole, not as a bunch of individual tones. If this is true then there can be no Doppler distortion in a speaker that is reproducing the signal in a linear manner. Doppler shift can only exist when one vibration is riding on another vibration or source of motion, it cannot exist when all vibrations are being produced as a single complex waveform. That is as simply as I can explain it. I'll go either way with the Doppler argument if someone can prove that the speaker isn't generating a complex waveform, but is generating a series of simple tones. The fact that I drove my big speakers with a 20Hz tone combined with a 500Hz tone at a level that the online proponents of Doppler distortion said would produce audible Doppler shift, and it didn't, tends to make me think that Doppler shift doesn't occur under those conditions. |
#82
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Randy Yates wrote: Proof by assertion? Sorry, Randy. I see nothing but proof by assertion from the supporters of "Doppler distortion." It shouldn't be incumbent on those that observe that no predictive theory exists to prove why it doesn't, although I've been trying, it should be incumbent on those claiming that it exists to produce the predictive theory. Have at it. This isn't string theory. If it's there, a precise model should almost fall out by inspection. Bob -- "Things should be described as simply as possible, but no simpler." A. Einstein |
#83
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Arny Krueger wrote: If you do the math, nonlinearities can't produce FM distoriton. You need something that operates in the time domain, not the amplitude domain. If you do the math, FM distortion and linearity are mutually exclusive. This is not debatable. Find a rigorous definition of linearity. I've presented it but it doesn't seem to have taken hold despite it being the bedrock of linear systems theory. Bob -- "Things should be described as simply as possible, but no simpler." A. Einstein |
#84
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Bob Cain writes:
Randy Yates wrote: Not. Get a clue, people. Doppler is a *PHYSICAL PHENOMENOM* that WILL happen whether or not you decide it can WHENEVER a sound wave source and observer are moving relative to each other. Period. This isn't open for debate. Randy has spoken. Without one shread of a predictive theory. Odd, that. Have you ever been to Ethiopia, Bob? We might as well be debating whether or not gravity exists there. I've never been - you've never been - so we can't say experientially, so it's open for doubt, right? -- % Randy Yates % "The dreamer, the unwoken fool - %% Fuquay-Varina, NC % in dreams, no pain will kiss the brow..." %%% 919-577-9882 % %%%% % 'Eldorado Overture', *Eldorado*, ELO http://home.earthlink.net/~yatescr |
#85
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"Porky" "Phil Allison" ** This little piggy cannot trot and chew gum at the same time. Are you kidding? ** Not one bit - you are clearly an utter imbecile. ................. Phil |
#86
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"Bob Cain" ** The original non ambulatory gum chewer. ........... Phil |
#87
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Bob Cain writes:
Randy Yates wrote: Proof by assertion? Sorry, Randy. I see nothing but proof by assertion from the supporters of "Doppler distortion." It shouldn't be incumbent on those that observe that no predictive theory exists to prove why it doesn't, although I've been trying, it should be incumbent on those claiming that it exists to produce the predictive theory. Have at it. This isn't string theory. If it's there, a precise model should almost fall out by inspection. If by "predictive theory" you mean a theory by which this phenomenom can be predicted, then I must ask if you are blind. I have stated it several times in several different ways. I have cited a reference for it (Halliday and Resnick). I am assuming you are familiar with the theory. Is that assumption invalid? Do you want a rehashing of the theory of the Doppler effect? Do you want me to transcribe my Physics text into a usenet news article for you so you don't have to go to the library and check one out? -- % Randy Yates % "Ticket to the moon, flight leaves here today %% Fuquay-Varina, NC % from Satellite 2" %%% 919-577-9882 % 'Ticket To The Moon' %%%% % *Time*, Electric Light Orchestra http://home.earthlink.net/~yatescr |
#88
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Bob Cain writes:
Randy Yates wrote: Proof by assertion? Sorry, Randy. I see nothing but proof by assertion from the supporters of "Doppler distortion." It shouldn't be incumbent on those that observe that no predictive theory exists to prove why it doesn't, although I've been trying, it should be incumbent on those claiming that it exists to produce the predictive theory. Have at it. This isn't string theory. If it's there, a precise model should almost fall out by inspection. I dunno Bob, are you SURE that current will flow when you place the 220 VAC electrodes across your temples? Why don't you try it. You never know - you may be in a reference frame in which Maxwell's equations no longer hold. -- % Randy Yates % "Ticket to the moon, flight leaves here today %% Fuquay-Varina, NC % from Satellite 2" %%% 919-577-9882 % 'Ticket To The Moon' %%%% % *Time*, Electric Light Orchestra http://home.earthlink.net/~yatescr |
#89
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"Bob Cain" Randy Yates wrote: Proof by assertion? Sorry, Randy. I see nothing but proof by assertion from the supporters of "Doppler distortion." ** Cos you are such an utter ass you refuse to see it. It shouldn't be incumbent on those that observe that no predictive theory exists ** What dishonest rot, Doppler theory is ancient. If it's there, a precise model should almost fall out by inspection. ** I posted a link with the maths of a precise model. Shame you are too big an ass to recognise it. ............ Phil |
#90
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"Bob Cain" If you do the math, FM distortion and linearity are mutually exclusive. ** Big lie. This is not debatable. ** The words of an ass. Find a rigorous definition of linearity. ** Find a relevant one. I've presented it but it doesn't seem to have taken hold despite it being the bedrock of linear systems theory. ** Another masive lie from a dangerous fool. ............... Phil |
#91
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"Bob Cain" What theoretical prediction might that be? I've yet to see a theory for "Doppler distortion" that predicts. Odd, that. ** This imbecile has never studied physics in his life. The kind in books OR the real world of nature. ........... Phil |
#92
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"Porky" ** This little piggy cannot trot and chew rotten fruit at the same time. .............. Phil |
#93
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"Porky" The fact that I drove my big speakers with a 20Hz tone combined with a 500Hz tone at a level that the online proponents of Doppler distortion said would produce audible Doppler shift, ** What level was that and WHO said so ???? ............. Phil |
#94
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Bob Cain writes:
If you do the math, FM distortion and linearity are mutually exclusive. This is not debatable. Find a rigorous definition of linearity. I've presented it but it doesn't seem to have taken hold despite it being the bedrock of linear systems theory. You need remedial work in logic, Bob. Even though the statement "A - B" may be true, there is nothing you can conclude if A is not true. "*IF* a system is linear, then it will not exhibit the Doppler effect" is a true statement. However, get this: T H E S Y S T E M I S N 'T L I N E A R !!!!!!!!!!!!!!! Note carefully, (for thine ist a beanhead): the "system" here is defined to be the entire electro-mechanical path from the speaker's electrical input to the acoustic receiver's input. -- % Randy Yates % "Maybe one day I'll feel her cold embrace, %% Fuquay-Varina, NC % and kiss her interface, %%% 919-577-9882 % til then, I'll leave her alone." %%%% % 'Yours Truly, 2095', *Time*, ELO http://home.earthlink.net/~yatescr |
#95
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Ben Bradley wrote: Someone should have just said at the start "Bob Cain (and a few others here) is in denial about the existence of Doppler effect in speakers" and I wouldn't have tried so hard... C'mon, Ben, let's not go there. I have skills in that direction too and would much rather keep them in their sheath. Let's keep this to techical give and take rather than resorting to that kind of stuff. How about giving us a predictive theory for "Doppler distortion" that can be tested against experiment? I have a predictive theory, the effect is zero for all signals and have proposed a simple, if not inexpensive, experiment that will remove from considerations all effects that the speaker mechanics have on the piston/air interface. Bob -- "Things should be described as simply as possible, but no simpler." A. Einstein |
#96
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"Phil Allison" wrote in message
... ** The words of an ass. Can't you do any better than calling people names? |
#97
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Ben Bradley wrote: But seriously, for Bob and other anti-doppler-distortion folks, how does cone-and-frame movement cause doppler while cone movement only does not? What is it about the frame that causes doppler? This is beginning to feel like an Einstein/Bohr debate. Not in the capabilities of the participants but in the nature of it. :-) My answer to this is that you must always consider the entire generating system. You must find the rest position of that entire system. In the frame of reference of (attached to) that rest position, there will be no "Doppler distortion." The air is capable of carrying any time varying signal but not an unvarying one. What it does in a frame of reference that is moving with constant velocity relative to that rest position is Doppler shift it. If the motion is varying in time it is linearly superimposed on the signal being emitted. Bob -- "Things should be described as simply as possible, but no simpler." A. Einstein |
#98
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Bob Cain writes:
Ben Bradley wrote: But seriously, for Bob and other anti-doppler-distortion folks, how does cone-and-frame movement cause doppler while cone movement only does not? What is it about the frame that causes doppler? This is beginning to feel like an Einstein/Bohr debate. Not in the capabilities of the participants but in the nature of it. :-) My answer to this is that you must always consider the entire generating system. "Entire generating system." Now there's an ill-defined statement. You must find the rest position of that entire system. In the frame of reference of (attached to) that rest position, there will be no "Doppler distortion." In the frame of reference of the acoustic emitter, there is no Doppler shift. That is certainly true. The air is capable of carrying any time varying signal but not an unvarying one. What it does in a frame of reference that is moving with constant velocity relative to that rest position is Doppler shift it. If the motion is varying in time it is linearly superimposed on the signal being emitted. Please explain to me why the wavelengths perceived by an observer experiencing a time-varying velocity relative to the source will not also experience a time-varying Doppler shift. -- % Randy Yates % "With time with what you've learned, %% Fuquay-Varina, NC % they'll kiss the ground you walk %%% 919-577-9882 % upon." %%%% % '21st Century Man', *Time*, ELO http://home.earthlink.net/~yatescr |
#99
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Randy Yates wrote: If by "predictive theory" you mean a theory by which this phenomenom can be predicted, then I must ask if you are blind. I have stated it several times in several different ways. I have cited a reference for it (Halliday and Resnick). I am assuming you are familiar with the theory. Is that assumption invalid? Do you want a rehashing of the theory of the Doppler effect? Do you want me to transcribe my Physics text into a usenet news article for you so you don't have to go to the library and check one out? It is hard for me to believe that you don't know that a predictive theory is one for which there is a mathematical model which can predict, with accuracy, the results of the kind of hypothetical situations that are being bandied about in order to compare measurement to theory. Where is it? Bob -- "Things should be described as simply as possible, but no simpler." A. Einstein |
#100
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"Phil Allison" wrote in message
... "Porky" "Phil Allison" ** This little piggy cannot trot and chew gum at the same time. Are you kidding? ** Not one bit - you are clearly an utter imbecile. And you are clearly a mental midget who must cover his ignorance with flippant comments and smart-alecky remarks which have nothing to do with the topic at hand. You are obviously in the wrong newsgroup, you should be in the alt.binaries.rotten-fruit-chewing-idiots group. From the scope of your input so far, you clearly have nothing to contribute to any of the groups this thread is a part of. Go crawl back under your rock, junior. To the rest of the members of the various groups, I apologize for the outburst, but this jerk started it and he clearly had it coming. |
#101
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Randy Yates wrote: "*IF* a system is linear, then it will not exhibit the Doppler effect" is a true statement. However, get this: T H E S Y S T E M I S N 'T L I N E A R !!!!!!!!!!!!!!! Well, Randy, many people are saying that it is and produces FM distortion anyway. Note carefully, (for thine ist a beanhead): the "system" here is defined to be the entire electro-mechanical path from the speaker's electrical input to the acoustic receiver's input. **** you, and I say that with all due respect. The system here is everything from the face of the piston on out. Nothing that occurs before that can be contributory and must be eliminated in some way from any experiment designed to catch Doppler at work. Again, give me a mathematical expression which describes in a quantitative way what should be measured at a distance from that speaker as a function of the motion of that speaker. Until that is done, "Doppler distortion" is not supported in theory. I sincerely hope no one will say that it isn't required because you see evidence of frequency modulation. According to a recent post, even that evidence may not really indicate frequency modulation but can be accounted for by non-linearity in the driver. I don't know the intricasies of modulation theory but it was said by someone who does that the data shown does not carry the signature of this supposed effect. Until "Doppler distortion" is supported in theory, and I hope all know by now what qualifies as a theory, there is no basis for it and no basis for correct interpretation of any measurement data. This is just basic science, folks. Bob -- "Things should be described as simply as possible, but no simpler." A. Einstein |
#102
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"Bob Cain" wrote in message ... Porky wrote: This whole argument is based on the wrong assumption that the high frequency source is "riding on" the low frequency source like a whistle on a train. It is NOT! Both sounds are being produced simultaneously by the complex electrical waveform driving the speaker cone which moves in accordance. Assuming that the speaker is being driven within its linear limits, the cone's motion accurately follows the driving signal, and it is a linear system. Forget the train/whistle anology, it is not an accurate representation for what goes on with a speaker, period! What he said. Is this the same Porky that I've argued with about _so_ many things? :-) Yep, I just had an attack of common sense before I started posting again. I decided to try to contribute positively to the group and to forget about any preconceived notions I may have had about group members. It seems that after doing so, my opinions of many of you went up quite a bit, which means that it was my misconceptions that were the problem. I apologize to all for that. Note that I'm not necessarily agreeing with you about Doppler distortion, but I am noting that most of those arguing in its favor are doing so on the basis of the train/whistle analogy which is an entirely different animal. Any theories based on that model don't necessarily apply to a "speaker cone driven by a single complex waveform" model. Unless someone can provide concrete proof based on real world measurements or provide an argument based on the "speaker cone driven by a single complex waveform" model, I'm still on the fence but leaning toward your side.:-) |
#103
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"Porky" "Phil Allison" ** This little piggy cannot trot and chew gum at the same time. Are you kidding? ** Not one bit - you are clearly an utter imbecile. And you are clearly a mental midget who must cover his ignorance with flippant comments and smart-alecky remarks which have nothing to do with the topic at hand. ** When I saw YOU doing EXACTLY that I gave up trying to correct you. I repeat : YOU are clearly an utter imbecile. ............. Phil |
#104
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"Randy Yates" wrote in message ... Bob Cain writes: Randy Yates wrote: Not. Get a clue, people. Doppler is a *PHYSICAL PHENOMENOM* that WILL happen whether or not you decide it can WHENEVER a sound wave source and observer are moving relative to each other. Period. This isn't open for debate. Randy has spoken. Without one shread of a predictive theory. Odd, that. Have you ever been to Ethiopia, Bob? We might as well be debating whether or not gravity exists there. I've never been - you've never been - so we can't say experientially, so it's open for doubt, right? -- Randy, it appears to me that you're still using the train/whistle model as a basis for the self-evidence of your claim, and if that model applied to this case you would be entirely correct. However it doesn't apply to loudspeakers producing complex waveforms. Your "gravity exists" example might be true under certain specific conditions, but if you're in a freefall dive in a plane over Ethiopia, gravity doesn't exist as far as you're concerned, at least until the plane starts pulling out of the dive. The problem here is whether the sound source is actually moving relative to the listener, when the source is a speaker being driven by a complex waveform. There are models that show that the actual source of the sound is a point or plane that lies approximately at the center of the motion described by the cone (I say approximately because the inertia of the cone and of the air it is acting on may move the source a bit). If these models are correct, then the source of the sound is not in motion relative to the listener and therefore Doppler distortion does not and cannot exist in a speaker. Certainly, this model, exact or not, is more accurate than the train/whistle model. |
#105
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"Phil Allison" wrote in message ... "Porky" ** This little piggy cannot trot and chew rotten fruit at the same time. Oh, Phil is repeating himself now, too bad it's just as insipid this time as it was the last. |
#106
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"Phil Allison" wrote in message ... "Porky" The fact that I drove my big speakers with a 20Hz tone combined with a 500Hz tone at a level that the online proponents of Doppler distortion said would produce audible Doppler shift, ** What level was that and WHO said so ???? It was from a website that one of the proponents of Doppler distortion posted. The peak velocity of my woofer exceeded that of the woofer in their experiment which meant I should have had a greater degree of Doppler distortion that that shown in their experiment, but there was none. Perhaps the original poster can repost the link, I haven't the time to go back and look it up, thugh I did refer to it in my original post concerning my experiment. |
#107
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Porky wrote: To the rest of the members of the various groups, I apologize for the outburst, but this jerk started it and he clearly had it coming. Problem is you gave him exactly what he was looking for. Ignore the troll. Starve him. Bob -- "Things should be described as simply as possible, but no simpler." A. Einstein |
#108
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"Porky" Randy, it appears to me that you're still using the train/whistle model as a basis for the self-evidence of your claim, and if that model applied to this case you would be entirely correct. However it doesn't apply to loudspeakers producing complex waveforms. ** Pure gobbledegook. The problem here is whether the sound source is actually moving relative to the listener, when the source is a speaker being driven by a complex waveform. ** The high frequency source is the one moving. There are models that show ..... ** Models are approximations to reality. that the actual source of the sound is a point or plane that lies approximately at the center of the motion described by the cone .... ** Even using such a model, that approximation is true only for single frequency operation. If these models are correct, then the source of the sound is not in motion relative to the listener and therefore Doppler distortion does not and cannot exist in a speaker. ** YOU are the one who is incorrect. Certainly, this model, exact or not, is more accurate than the train/whistle model. ** Not one bit - you are clearly an utter imbecile. .............. Phil |
#109
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"Porky" "Phil Allison" ** This little piggy cannot trot and chew rotten fruit at the same time. Oh, Phil is repeating himself now, too bad it's just as insipid this time as it was the last. ** Not one bit - you are clearly an utter imbecile. Oink oink oink oink oikk ....... ............... Phil |
#110
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Porky wrote: What he said. Is this the same Porky that I've argued with about _so_ many things? :-) Yep, I just had an attack of common sense before I started posting again. I decided to try to contribute positively to the group and to forget about any preconceived notions I may have had about group members. It seems that after doing so, my opinions of many of you went up quite a bit, which means that it was my misconceptions that were the problem. I apologize to all for that. Wow. You don't often encounter that. Well done and welcome. Note that I'm not necessarily agreeing with you about Doppler distortion, but I am noting that most of those arguing in its favor are doing so on the basis of the train/whistle analogy which is an entirely different animal. Any theories based on that model don't necessarily apply to a "speaker cone driven by a single complex waveform" model. Unless someone can provide concrete proof based on real world measurements or provide an argument based on the "speaker cone driven by a single complex waveform" model, I'm still on the fence but leaning toward your side.:-) Well, everything you've offered is technically spot on. I think you'll find the right conclusion. Bob -- "Things should be described as simply as possible, but no simpler." A. Einstein |
#111
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Randy Yates wrote: Bob Cain writes: Randy Yates wrote: Not. Get a clue, people. Doppler is a *PHYSICAL PHENOMENOM* that WILL happen whether or not you decide it can WHENEVER a sound wave source and observer are moving relative to each other. Period. This isn't open for debate. Randy has spoken. Without one shread of a predictive theory. Odd, that. Have you ever been to Ethiopia, Bob? We might as well be debating whether or not gravity exists there. I've never been - you've never been - so we can't say experientially, so it's open for doubt, right? Randy, do you really think that if this complex interaction is real, there needn't be a mathematical expression which describes the effect on any signal in a way that is subject to experimental verification? Bob -- "Things should be described as simply as possible, but no simpler." A. Einstein |
#112
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"Porky" "Phil Allison" The fact that I drove my big speakers with a 20Hz tone combined with a 500Hz tone at a level that the online proponents of Doppler distortion said would produce audible Doppler shift, ** What level was that and WHO said so ???? It was from a website that one of the proponents of Doppler distortion posted. ** Get real - post the details. The peak velocity of my woofer exceeded that of the woofer in their experiment ** At only 20 Hz ???? Get real. which meant I should have had a greater degree of Doppler distortion that that shown in their experiment, but there was none. ** Not one poster here has said Doppler shift is readily audible from such a test. It has been said *repeatedly* that it will be swamped by intermodulation effects. Perhaps the original poster can repost the link, I haven't the time to go back and look it up, ** Liar. ............... Phil |
#113
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Randy Yates wrote: "Entire generating system." Now there's an ill-defined statement. So thought Einstein when Bohr offered it in refutation of one of his many challenges. :-) Bob -- "Things should be described as simply as possible, but no simpler." A. Einstein |
#114
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Randy Yates wrote: Please explain to me why the wavelengths perceived by an observer experiencing a time-varying velocity relative to the source will not also experience a time-varying Doppler shift. Because the air can carry the time varying signal. Bob -- "Things should be described as simply as possible, but no simpler." A. Einstein |
#115
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"Randy Yates" wrote in message ... Bob Cain writes: Ben Bradley wrote: But seriously, for Bob and other anti-doppler-distortion folks, how does cone-and-frame movement cause doppler while cone movement only does not? What is it about the frame that causes doppler? This is beginning to feel like an Einstein/Bohr debate. Not in the capabilities of the participants but in the nature of it. :-) My answer to this is that you must always consider the entire generating system. "Entire generating system." Now there's an ill-defined statement. You must find the rest position of that entire system. In the frame of reference of (attached to) that rest position, there will be no "Doppler distortion." In the frame of reference of the acoustic emitter, there is no Doppler shift. That is certainly true. The air is capable of carrying any time varying signal but not an unvarying one. What it does in a frame of reference that is moving with constant velocity relative to that rest position is Doppler shift it. If the motion is varying in time it is linearly superimposed on the signal being emitted. Please explain to me why the wavelengths perceived by an observer experiencing a time-varying velocity relative to the source will not also experience a time-varying Doppler shift. -- The simple answer is that while the cone's movement provides the energy for the sound, there is a conversion of air motion to pressure waves (sound waves) which does not occur within or on the cone's surface, thus the actual sound source is not the speaker cone, it is the point or plane where the air motion to pressure wave conversion takes place. |
#116
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#117
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"Bob Cain" Porky wrote: To the rest of the members of the various groups, I apologize for the outburst, but this jerk started it and he clearly had it coming. Problem is you gave him exactly what he was looking for. Ignore the troll. Starve him. ** ROTFLMAO !!! What the hell do you think Bob Cain is doing right now if not carrying on the biggest, dumbest, most pathetic damn troll this NG has seen in years. You are all having your legs pulled - right off !! ................. Phil |
#118
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"Phil Allison" wrote in message ... "Bob Cain" Porky wrote: To the rest of the members of the various groups, I apologize for the outburst, but this jerk started it and he clearly had it coming. Problem is you gave him exactly what he was looking for. Ignore the troll. Starve him. ** ROTFLMAO !!! What the hell do you think Bob Cain is doing right now if not carrying on the biggest, dumbest, most pathetic damn troll this NG has seen in years. You are all having your legs pulled - right off !! Phil, I believe that you are misspelling your name, it obviously should be "Phool"! What you're pulling on isn't a topic for discussion among decent folk... |
#119
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"Porky" writes:
[...] Please explain to me why the wavelengths perceived by an observer experiencing a time-varying velocity relative to the source will not also experience a time-varying Doppler shift. -- The simple answer It's OK, you can use big words and math with me. I'm a big boy now. is that while the cone's movement provides the energy for the sound, there is a conversion of air motion to pressure waves (sound waves) which does not occur within or on the cone's surface, thus the actual sound source is not the speaker cone, it is the point or plane where the air motion to pressure wave conversion takes place. Accepting this assertion as true for the moment, why wouldn't the position of this "point or plane" be a function of the position of the cone? Thus, again, this point would move along with the low-frequency energy. Also, a) where did this theory of "air motion to pressure waves" come from, and b)why did you wait some 20 or 30 posts before coming out with this as your main basis for why Doppler does not occur? -- % Randy Yates % "With time with what you've learned, %% Fuquay-Varina, NC % they'll kiss the ground you walk %%% 919-577-9882 % upon." %%%% % '21st Century Man', *Time*, ELO http://home.earthlink.net/~yatescr |
#120
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"Randy Yates" wrote in message ... "Porky" writes: [...] Please explain to me why the wavelengths perceived by an observer experiencing a time-varying velocity relative to the source will not also experience a time-varying Doppler shift. -- The simple answer It's OK, you can use big words and math with me. I'm a big boy now. is that while the cone's movement provides the energy for the sound, there is a conversion of air motion to pressure waves (sound waves) which does not occur within or on the cone's surface, thus the actual sound source is not the speaker cone, it is the point or plane where the air motion to pressure wave conversion takes place. Accepting this assertion as true for the moment, why wouldn't the position of this "point or plane" be a function of the position of the cone? Thus, again, this point would move along with the low-frequency energy. That's where it gets tricky, but I've long seen it referred to as a "point" source or a "planar" source, and for whatever reason it's treated as a non-moving stable source. I believe that it has to do with the air's mass and inertia, but as I said, the actual physics will have to be figured out by those with a higher education than I have. This actually goes back at least as far as the '60's and possibly much earlier. That's the reason I didn't advance it sooner, it just didn't occur to me. I was just following the reasoning that the speaker cone actually generated the sound, until it finally occurred to me that it doesn't, whatever is producing the actual sound waves has to be moving at the speed of sound to impart the necessary pressure wave, and this is the interface where molecular motion is converted to pressure waves. Think about it, if the speaker pushes a volume of air forward, it will be moving at the same speed as the cone that imparted the motion, and it won't be sound, it will be a slowly moving volume of air. When the molecules in that volume of air meet other molecules, the slow motion of molecules is converted into a high velocity pressure wave where it is the pressure wave that is moving and not the air itself, just like an ocean wave. This is a dynamic process and the back and forth motion of the cone has nothing to do with it as far as the sound's source point is concerned. I can see how it happens and understand it quite well, but I simply haven't got the math or physics background to do the equations. Also, a) where did this theory of "air motion to pressure waves" come from, and b)why did you wait some 20 or 30 posts before coming out with this as your main basis for why Doppler does not occur? As I said, it just occurred to me that the speaker cone doesn't produce the sound, the air does. It's been a long time since I'd thought about it because the model goes back a long way. Before this, I was on the fence, though I was leaning toward the "no Doppler" side, I suppose because this was rolling around in my subconscience. I knew that there was something wrong with the train/whistle model, and I was thinking all along that it was the multiple simple sources vs the single complex source, but that wasn't it, this was. "The sound wave may be considered as holographic in nature, and just like a visual hologram doesn't appear on the surface of the holographic plate, neither does the sound wave originate on the surface of the speaker cone." I have no idea whom I'm quoting, but I remember the quote from some text or other I read quite a few years ago. The words may not be exact, but the gist is the same. |
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