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#281
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William Sommerwerck wrote:
That's what I was saying, that any tone would warp its own waveshape due to Doppler shift. It doesn't, though, because there's only one motion. Doppler requires two motions -- the wave, and the movement of the surface producing it. LOL |
#282
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"Jim Carr" wrote in message news:LIzUc.9970$yh.371@fed1read05...
Bob can correct me here, but from where I sit, Bob does not deny the Doppler shift. He completely accepts the formula fo = fs . (v - vo) / (v - vs). What he does not accept is that you can insert the speaker diaphragm's movement as vs. He accepts that you can put the speaker on the train and predict the Doppler shift with the above formula as does everyone he's arguing with. But here's the kicker: Either the above formula is wrong, there is no Doppler Distortion, or somebody left out an assumption somewhere. Why? Because the formula does not take into consideration the movement of the diaphragm. If the source and observer are not moving, there is no Doppler shift, right? But according to the proponents of Doppler Distortion, there *is* a shift. Everything that creates sound moves in some way. So why hasn't someone updated that formula? The problem isn't that somebody left out an assumption somewhere. The problem is that nobody involved in the discussion of this topic thus far seems to have asked the question "upon what assumption is the derivation of the formula based" Consequently those like Bob Cain, who foolishly deny the existence of demonstrated reality, "assume" that the equation that is cited for the constant-velocity case does not also apply to the dynamic case. On the other hand, those with a bit more common technical sense than Bob Cain similarly "assume" that the equation applies to the dynamic case as well as to the constant velocity case. The problem is that, for whatever reason, no one debating the issue seems to actually know which of the two mutually exclusive assumptions is correct. Those who are interested in knowing can find the answer as well as the derivation from fundamental principles of the formula for instantaneous Doppler shift in Allan Pierce's book "Acoustics, An Introduction to Its Physical Principles and Applications." |
#283
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"Jim Carr" wrote in message news:LIzUc.9970$yh.371@fed1read05...
Bob can correct me here, but from where I sit, Bob does not deny the Doppler shift. He completely accepts the formula fo = fs . (v - vo) / (v - vs). What he does not accept is that you can insert the speaker diaphragm's movement as vs. He accepts that you can put the speaker on the train and predict the Doppler shift with the above formula as does everyone he's arguing with. But here's the kicker: Either the above formula is wrong, there is no Doppler Distortion, or somebody left out an assumption somewhere. Why? Because the formula does not take into consideration the movement of the diaphragm. If the source and observer are not moving, there is no Doppler shift, right? But according to the proponents of Doppler Distortion, there *is* a shift. Everything that creates sound moves in some way. So why hasn't someone updated that formula? The problem isn't that somebody left out an assumption somewhere. The problem is that nobody involved in the discussion of this topic thus far seems to have asked the question "upon what assumption is the derivation of the formula based" Consequently those like Bob Cain, who foolishly deny the existence of demonstrated reality, "assume" that the equation that is cited for the constant-velocity case does not also apply to the dynamic case. On the other hand, those with a bit more common technical sense than Bob Cain similarly "assume" that the equation applies to the dynamic case as well as to the constant velocity case. The problem is that, for whatever reason, no one debating the issue seems to actually know which of the two mutually exclusive assumptions is correct. Those who are interested in knowing can find the answer as well as the derivation from fundamental principles of the formula for instantaneous Doppler shift in Allan Pierce's book "Acoustics, An Introduction to Its Physical Principles and Applications." |
#284
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The problem isn't that somebody left out an assumption somewhere. The
problem is that nobody involved in the discussion of this topic thus far seems to have asked the question "upon what assumption is the derivation of the formula based" Consequently those like Bob Cain, who foolishly deny the existence of demonstrated reality, "assume" that the equation that is cited for the constant-velocity case does not also apply to the dynamic case. On the other hand, those with a bit more common technical sense than Bob Cain similarly "assume" that the equation applies to the dynamic case as well as to the constant velocity case. The problem is that, for whatever reason, no one debating the issue seems to actually know which of the two mutually exclusive assumptions is correct. Those who are interested in knowing can find the answer as well as the derivation from fundamental principles of the formula for instantaneous Doppler shift in Allan Pierce's book "Acoustics, An Introduction to Its Physical Principles and Applications." In terms of the question Bob Cain initially asked, the formula doesn't matter, because Doppler shift exists regardless of whether you're working in constant-velocity medium ("the luminiferous ether") or a non-constant-velocity medium (air). The formulas are different, but that doesn't have anything to do with the nature of the argument. |
#286
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Scott Dorsey wrote: Bob Cain wrote: The system by which a single ideal speaker surface transduces an electrical waveform my moving and producing a series of travelling pressure changes in the air is *not* a linear system. Please prove that. It has yet to be done. I can prove that easily, but not in any way that has anything to do with doppler effect. There are plenty of amplitude nonlinearities, from a dead band due to spider friction, to break-up modes at high levels. But none of them have anything to do with the doppler issues. Right. The doppler issues, though, don't have anything to do with amplitude nonlinearities. The earlier reference made to Terman is a good one. I'm still hoping someone with access to a source containing the expression describing pressure/velocity in the wave as a function of the velocity of the piston will transcribe it to one of these threads. If it exists, it's just an equation. If it doesn't, we simply _must_ consider why that is. Bob -- "Things should be described as simply as possible, but no simpler." A. Einstein |
#287
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William Sommerwerck wrote: The behavior of the system is FULLY predicted by the Doppler formula, where THE VELOCITY OF THE CONE MOTION (as produced by the lower tone) IS THE SOURCE VELOCITY. That's all there is to it. It's no more complex than that. All you have to do is plug and grind. The expression Jim showed is only valid for the various velocities being constant. Nowhere that I've seen that expression has a dynamic situation been under discussion. The dynmaics are included in the fs term. There is a reason for that. Doppler shift only applies to constant velocity components. The time varying ones are incorporated correctly in the generated wave. Bob -- "Things should be described as simply as possible, but no simpler." A. Einstein |
#288
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so what wrote: That's what I was saying, that any tone would warp its own waveshape due to Doppler shift. Under the flawed "analysis" that has been historically presented, this is an inescapable conclusion. No linear system is capable of producing frequency components in its output that aren't in its input and no non-linear system can produce exactly the input frequency and no others for all sin waves. This is fundamental. A system is either linear or it isn't. There is no in-between to accomodate this hypothetical "Doppler distortion." Bob -- "Things should be described as simply as possible, but no simpler." A. Einstein |
#289
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The Ghost wrote: The problem isn't that somebody left out an assumption somewhere. The problem is that nobody involved in the discussion of this topic thus far seems to have asked the question "upon what assumption is the derivation of the formula based" Consequently those like Bob Cain, who foolishly deny the existence of demonstrated reality, "assume" that the equation that is cited for the constant-velocity case does not also apply to the dynamic case. On the other hand, those with a bit more common technical sense than Bob Cain similarly "assume" that the equation applies to the dynamic case as well as to the constant velocity case. The problem is that, for whatever reason, no one debating the issue seems to actually know which of the two mutually exclusive assumptions is correct. Those who are interested in knowing can find the answer as well as the derivation from fundamental principles of the formula for instantaneous Doppler shift in Allan Pierce's book "Acoustics, An Introduction to Its Physical Principles and Applications." Why don't you consider actually contributing something of substance to this conversation? I know you are capable. Bob -- "Things should be described as simply as possible, but no simpler." A. Einstein |
#290
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"Jim Carr" wrote in message news:LIzUc.9970$yh.371@fed1read05...
Bob can correct me here, but from where I sit, Bob does not deny the Doppler shift. He completely accepts the formula fo = fs . (v - vo) / (v - vs). What he does not accept is that you can insert the speaker diaphragm's movement as vs. He accepts that you can put the speaker on the train and predict the Doppler shift with the above formula as does everyone he's arguing with. But here's the kicker: Either the above formula is wrong, there is no Doppler Distortion, or somebody left out an assumption somewhere. Why? Because the formula does not take into consideration the movement of the diaphragm. If the source and observer are not moving, there is no Doppler shift, right? But according to the proponents of Doppler Distortion, there *is* a shift. Everything that creates sound moves in some way. So why hasn't someone updated that formula? The problem isn't that somebody left out an assumption somewhere. The problem is that nobody involved in the discussion of this topic thus far seems to have asked the question "upon what assumption is the derivation of the formula based" Consequently those like Bob Cain, who foolishly deny the existence of demonstrated reality, "assume" that the equation that is cited for the constant-velocity case does not also apply to the dynamic case. On the other hand, those with a bit more common technical sense than Bob Cain similarly "assume" that the equation applies to the dynamic case as well as to the constant velocity case. The problem is that, for whatever reason, no one debating the issue seems to actually know which of the two mutually exclusive assumptions is correct. Those who are interested in knowing can find the answer as well as the derivation from fundamental principles of the formula for instantaneous Doppler shift in Allan Pierce's book "Acoustics, An Introduction to Its Physical Principles and Applications." |
#291
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Scott Dorsey wrote: Actually, to do it in the time domain, it takes a Bessel function. The reference to Terman is an excellent one. Scott, if you have that reference, would you _please_ transcribe here the expression that is the end result of analyzing "Doppler distortion"? I'll owe you a big one. Bob -- "Things should be described as simply as possible, but no simpler." A. Einstein |
#292
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Scott Dorsey wrote: No, it should change it a little bit. Of course, the ratio between the volume of the box behind the piston and the volume of the earth's atmosphere is very small. But it's nonzero! I'm afraid that's wrong, Scott. Anything producing Doppler shift changes the global atmospheric pressure not a whit. It's not asymptotically zero, it's zero, nuttin, nada. :-) Bob -- "Things should be described as simply as possible, but no simpler." A. Einstein |
#293
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The expression Jim showed is only valid for the various
velocities being constant. Nowhere that I've seen that expression has a dynamic situation been under discussion. The dynmaics are included in the fs term. There is a reason for that. Doppler shift only applies to constant velocity components. The time varying ones are incorporated correctly in the generated wave. No, no, no, no, no... If the train speeds up or slows down, you will the magnitude of the Doppler shift change. |
#294
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No, no, no, no, no... If the train speeds up or slows down, you will the
magnitude of the Doppler shift change. God, I'm getting careless in my geezerhood... No, no, no, no, no... If the train speeds up or slows down, the Doppler shift will still be audible. Only its magnitude will change. |
#295
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In alt.music.home-studio,rec.audio.tech,rec.audio.pro, Bob Cain
wrote: so what wrote: That's what I was saying, that any tone would warp its own waveshape due to Doppler shift. Under the flawed "analysis" that has been historically presented, this is an inescapable conclusion. No linear system is capable of producing frequency components in its output that aren't in its input and no non-linear system can produce exactly the input frequency and no others for all sin waves. This is fundamental. Let's pull the head of an engine to expose the piston, and spin this thing fast enough that the piston exceeds the speed of sound at its maximum speed. For a couple of inches stroke length, this will probably be about 5kHz, and the crank will really be spinning at 30,000 RPM. But hey, the piston is tracing through a sine wave, isn't it? A system is either linear or it isn't. There is no in-between to accomodate this hypothetical "Doppler distortion." It's not in-between, it's a non-linear* system. Bob * A definition that works here is that there's at least one frequency in the output that's not in the input. I was going to say that a definition that doesn't work is that if a system has "amplitude linearity" it's a linear system, but even in the doppler distortion case, the FM'ed frequency has its fundamental frequency lowered as the sidebands take power. So it's both a distortting and a non-linear system no matter how you define those terms. ----- http://mindspring.com/~benbradley |
#296
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William Sommerwerck wrote: The expression Jim showed is only valid for the various velocities being constant. Nowhere that I've seen that expression has a dynamic situation been under discussion. The dynmaics are included in the fs term. There is a reason for that. Doppler shift only applies to constant velocity components. The time varying ones are incorporated correctly in the generated wave. No, no, no, no, no... If the train speeds up or slows down, you will the magnitude of the Doppler shift change. Here is where it goes from black and white to something gray. In the free, far field, from a piston very small relative to the wavelength, it isn't necessasary to get all the way to DC for the system to lose the ability to generate the lowest frequency components in any signifigant way relative to the receiver. In that frequency region, "Doppler distortion" should evidence itself. This would only happen at DC in the closed, infinite tube with a piston in it that I've been employing as a simplified toy system. Whenever the piston/air is able to well support the bandwidth, however, I don't believe "Doppler distortion" can be demonstrated. The motion will be incorporated in the generated wave in a linear fashion. BTW, I am in discussion right now with Art Ludwig about this. At this point we are just settling on the correct situation to analyze. Hopefully a definitive answer will come out of our discussion. Bob -- "Things should be described as simply as possible, but no simpler." A. Einstein |
#297
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"Jonas P Eckerman" ** This man has mental disabilities. |
#298
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"Bob Cain" wrote in message ... Porky wrote: thing and start from scratch, I think you'll see what Bob and I see. Remember two things, an oscilloscope pattern is at best a two dimensional representation of a three dimensional occurance and doesn't necessarily represent what is actually happening, and the speaker cone doesn't actually generate the sound wave (velocity too low and p-p cone travel too short for the wavelength), the air it moves does. No, the cone is actually moving with the right velocity for the wave, and it is in the right position to impart that to the air because its derivative gives the position in the wave where that velocity applies and that's just where it happens to be. Unless it's a constant component and then it can't impart that to the air so it's position is in error. That error is Doppler shift. Well, the cone is oscillating at the same frequency as the wave it's producing, but there's still the matter of the low velocity of the air molecules it's moving being converted to the high velocity soundwave that we hear. I think I see what you're saying though. |
#299
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Ben Bradley wrote: Let's pull the head of an engine to expose the piston, and spin this thing fast enough that the piston exceeds the speed of sound at its maximum speed. For a couple of inches stroke length, this will probably be about 5kHz, and the crank will really be spinning at 30,000 RPM. But hey, the piston is tracing through a sine wave, isn't it? Uh, when did moving faster than the speed of sound enter the discussion? A system is either linear or it isn't. There is no in-between to accomodate this hypothetical "Doppler distortion." It's not in-between, it's a non-linear* system. Then single frequency inputs are also distorted by the phenomenon we are discussing, right? * A definition that works here is that there's at least one frequency in the output that's not in the input. Ok. Close enough for horse shoes. Bob -- "Things should be described as simply as possible, but no simpler." A. Einstein |
#300
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"Phil Allison" wrote in message ... "Porky" Ignore Phil, he's just mad because he can't contribute anything positive to this discussion, he has neither the education nor the intelligence, ** You are well named - except pigs revelling in **** have more sense and manners than you do. FYI I studied physics at the University of Sydney at honours level. My IQ is at least double yours. Unlike you and Bob, I do not have mental disabilities. Oh, wow! Your IQ would be something a bit over 280, in that case. You may have studied physics, but you have yet to show that you benefitted in any manner from your studying. You may or may not have a mental disability, but you certainly have a major social disability. |
#301
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"Arny Krueger" wrote in message ... "Ben Bradley" wrote in message Arny, I can see a reluctance to even look, as the spectrum of an FM signal is SO counterintuitive (at least to me) that it's actually hard to believe (and thus the 'flattop' comment we saw earlier). Really? It's fairly intuitive to me. However, not everybody spent three years trying to grok Doppler radars that had LAYERS of AM & FM modulators in both the transmitter and receiver. That was a long time ago, but it seems to have stuck, at least a little. Mine was Nike HiPAR and Nike missile and tracking radars, and it was many years ago as well. I do 'believe' the sidebands are as you say they are, but can't imagine how FM results in those sidebands. The 50 Hz part I understand. The phase inversion of the upper sidebands I understand. The multiple sidebands I take based on more-or-less faith, based on knowlege of Bessel functions and many hours spent with spectrum analyzers. Perhaps those with knowledge of higher math (more than a couple quarters of calculus) can visualize it. In the end, I think it is experience. The ultimate proof is when it works as predicted, theory and empirical knowlege tell the same story. The experiment I suggested will give the results I gave, and if it is right at under the circumstances I suggested, it should be right under all circumstances with the same conditions, right? In other words, if it applies with a LF of .1 Hz or 1 Hz, it will still apply at LF's 20Hz or 50Hz, is that not correct? I'm not trying to say that there won't be other things that happen under real world conditions, including what other folks have observed and stated, I'm just saying they won't be because of Doppler distortion. Doppler shift is a special case, and it is certainly real, and it can even be produced with a speaker (the Leslie speaker is a good case), but the shift isn't produced by the cone motion, it is produced by moving the speaker, or more accurately the mouth of the baffle (the HF horn and the LF baffle rotating). |
#302
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"Bob Cain" wrote in message ... Porky wrote: Bob, aren't they showing a 1KHz signal modulated with a 50 Hz signal? That isn't what happens with Doppler shift, the modulation frequency will depend on the velocity of the source, not its frequency of oscillation, and it sure won't be sidebands at +-50Hz!, more like +-3 or 4Hz! If I'm right, this is an example of the fundamental mis-assumptions the pro-Doppler group is making, just like basing their logic on an analogy that doesn't meet the necessary criteria.. Something quite like that is what my inuition says too but without a deeper analysis and a better understanding of modulation theory I don't trust my intuition on this one. The actual frequency modulation would be determined by the velocity of the cone, wouldn't it? It would be a shift of X Hz varying back and forth at the rate of the LF, and it would (and did, in my experiment) result in the HF tone showing as a table top from HF-shift to HF+shift. I found a wave of a train whistle on a train passing, at http://weathersavvy.com/Doppler3.html, and recorded it, trimmed off the conductor's voice and analyzed the entire wave in Cool Edit 96, the result was multiple peaks due to the harmonic content of the whistle, but they were all wide and of the roughly table top variety, and with no sidebands. |
#303
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Bob Cain wrote in message ...
Why don't you consider actually contributing something of substance to this conversation? I know you are capable. I have, but you are too stupid to recognize it. |
#304
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Bob Cain wrote in message ...
Why don't you consider actually contributing something of substance to this conversation? I know you are capable. I have, but you are too stupid to recognize it. |
#305
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Bob Cain wrote in message ...
Why don't you consider actually contributing something of substance to this conversation? I know you are capable. I have, but you are too stupid to recognize it. |
#306
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Bob Cain wrote in message ...
Why don't you consider actually contributing something of substance to this conversation? I know you are capable. I have, but you are too stupid to recognize it. |
#307
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"Porky" Well, the cone is oscillating at the same frequency as the wave it's producing, but there's still the matter of the low velocity of the air molecules it's moving being converted to the high velocity soundwave that we hear. I think I see what you're saying though. ** Air molecules are never slow moving - their average speed is some 46 % greater than the speed of a sound wave. ............. Phil |
#308
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"Arny Krueger" wrote in message ... However this is NOT what we are doing here, we are dealing with a special case of frequency shift, Doppler shift, and we most certainly are not modulating the carrier (HF tone) with a LF tone. Totally wrong. We are exactly modulating the HF tone with a LF tone, but its a bit confusing becasue there is both AM and FM and you clearly don't get FM. Once again, we are NOT modulating the Hf tone with a LF tone, we are modulating the HF tone with the supposed Doppler shift caused by the VELOCITY of the cone moving toward us and away from us! But the toward/away motion is exactly due to the LF tone. But the Doppler component is solely due to the velocity of the speaker cone, and a fair model will be one P-P cycle, because the exact same thing occurs every cycle, so the LF frequency has absolutely nothing to do with the doppler shift. Since Doppler shift is supposed to occur any time the source is moving toward or away from the listener, the rate of the cone's moving back and forth doesn't matter, it's the velocity of the cone supposedly causing the shift in frequency! The velocity of the cone and the rate of the cone's motion are closely tied together. The frequency is NOT relevant to Doppler, and in fact, the spectrum analyzer's resolution when examining multiple cycles may be contributing to the confusion. In our example, the cone's frequency remains constant, the velocity varies with the amplitude of the cone's motion. Of course that only applies directly as long as the cone doesn't exceed it's linear excursion limits, but that's not Doppler. Again, what happens in any one p-p cycle is exactly replicated in every other cycle, so a single cycle is sufficient for predictive analysis. We are supposedly Doppler shifting the carrier frequency by some amount, depending on the cone velocity of the speaker. Right, which produces discrete sidebands that differ from the carrier by multiples of the modulating frequency. Try my experiment and see what you get, you are still thinking in terms of the LF tone modulating the HF tone and that ISN"T what's happening with Doppler shift! I've both done and debunked your experiment. Next! In what way? If you did what I said, you got a roughly tabletop waveform with no sidebands. Forget about multiple cycles, reduce it to a single cycle which will give you all the info you need for the purpose of analyzing Doppler shift, if you scan the entire cycle. The Doppler shift is strictly a matter of the velocity of a sound source in relation to a listener, that's how Doppler is defined, it has nothing to do with how often the source changes direction!!! But it does. If the source doesn't change direction often enough, and the peak velocity is high enough, the cone comes sailing out of the woofer frame, destroying the woofer. Which has absolutely nothing to do with Doppler shift! The cyclic changing direction creates the sidebands we observe. But what do they have to do with doppler shift? the answer is, "Nothing!" If you go from 500 to 600Hz and then back to 500, then you are simulating one cycle of the speaker cone. Whether the motion is linear or sinusoid won't matter. Oh but it does. A linear motion is characteristic of a sawtooth modulating wave, and that gives a different collection of sidebands. You convolve the spectrum of the carrier with the spectrum of the modulating signal.... But even if you apply a sinusiod frequency modulation to a single cycle, you still get the roughly tabletop waveform. What applies to one cycle will apply to every other cycle. Nope, the shape of the cycle matters. I didn't say the shape didn't matter, the shape of the top of the wave will vary depending on if the velocity is linear or in a sine pattern, but it remains a rough tabletop regardless. Perhaps I should have said, what happens in any one cycle will be repeated in every other identical cycle, and will be similar in pattern even in non-identical cycles. You can take a single cycle at any LF with any HF Tone and any real world possibility of waveshape of the LF component (no squarewaves, that isn't possible with a loud speaker), and the result will still be a roughly tabletop wave extending from HF-shift to HF+shift. That is an accurate simulation of Doppler shift. If Doppler shift exists, the result will be a table top, if not Wc will be represented as a spike. Try it! Were talking about a speaker cone that moves in a periodic cycle, not a train on a tabletop. Go ahead, try it, go back and forth from one frequency to the other as many times as you wish, the results will be the same! Trust me, I've tried a ton of things. Try this, generate a 20 second waveform of 500 Hz being modulated by 100 hz at a modulation frequency of .1 hz. this represents a HF tone of 500 Hz being moved on a giant speaker moving at a velocity high enough to result in a Doppler shift of +-20% with a LF component of .1 Hz. for two full p-p cycles. OK, its on the screen before me in Audition/CE Note that you will see the same tabletop at higher frequencies if your resolution is fine enough. Nope. I see a spike at whatever frequency the carrrier is at, where my analysis intersects it. I wish that people would do their own home work. (I used an FFT of 65536 Blackman-Harris) That is what I use. BTW, Audition/CE does not animate the spectral display when you play a file. That is as far as I can take this, but it seems adequate to me. I don't think you understand the relevance of the time period over which the analysis is performed. The issue of Doppler distortion is related to the relative velocity of the listener and source, So far so good. nothing in Doppler theory suggests that the frequency of change of direction will have anything to do with the amount of frequency shift. True, but the frequency of shift and the frequency of the sidebands are two vastly different things. If the change of direction is such that the velocity graph forms a sine wave, the amount of shift will vary with the changing velocity from instant to instant, but the result will still be a varying amount of shift directly related to the instantaneous velocity at the time of measurement, and the result, assuming high enough resolution of the analyzer will be some form of tabletop waveform that varies from Wc minus shift to Wc plus shift. OK, I think I follow this. If you see this tabletop wave when recording a speaker producing a complex waveform consisting of a HF and a LF component, Doppler distortion exists in a speaker, if you don't, it doesn't. In fact, an ideal frequency domain analysis will show a moving spike. Your tabletop is an artifact of the length of your sample, which is in turn determined by the sample size. If you analyze a wave during a time period when it has components at a range of frequencies (this time because the frequency is slowly changing) then you get your tabletop. A 65k point FFT is inappropriate for analyzing a wave with a modulation frequency of 0.1 Hz. 0.1 Hz corresponds to 10 seconds of data. Normally, we would use a FFT that covered several times that much data to reveal the sideband structure. A 44100 Hz you need a FFT that would be appropriate would have like 4 million points or more. I tried it with my speakers and I didn't see it on the scan (no side bands either) or hear it on playback. You picked a demonstration that is inapprorpiate for the data at hand. Futhermore its not representaive of speakers, because it is based on a 1/10 th Hz modulating frequency. As I said, that's as far as I can go with this, those with advanced education can debate further if they desire, but I've reached my limit and this time I'm going to respect that.:-) You've wasted both of our time with a very poorly-formed experiment. ;-( |
#309
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"Porky" "Phil Allison" Ignore Phil, he's just mad because he can't contribute anything positive to this discussion, he has neither the education nor the intelligence, ** You are well named - except pigs revelling in **** have more sense and manners than you do. FYI I studied physics at the University of Sydney at honours level. My IQ is at least double yours. Unlike you and Bob, I do not have mental disabilities. Oh, wow! Your IQ would be something a bit over 280, in that case. ** Wrong direction Porker - yours is only about 85. Plus you are autistic. Learning to sing yet ??? .......... Phil |
#310
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I think I'm closing in on the truth here and, as usual, we are (mostly) all right in some regards and are all wrong in some. First, my analysis of what happens in an infinite tube containing a piston is wrong in the case of a constant velocity component. If the piston contains no constant velocity component then the propegating wave will be a reproduction of the velocity of the piston because its position is always in proper correspondence to the velocity it is imparting so as to impart no error. The usual intuitive rationalization for Doppler distortion is just wrong. The process is linear and real in this case. However, my belief that in the tube a piston of constant velocity imparts no constant velocity to the wave was wrong as shown he http://www.silcom.com/~aludwig/Physi...collisions.htm The upshot is that there is no Doppler distortion in an infinite tube with a driving piston in it for any signal (until the piston smacks into the receiver if moving toward it. :-) In all other configurations, no Doppler distortion will occur among components within the portion of its passband that is fairly flat. It is the difference in the coupling between the piston and the air at different frequencies that produces Doppler distortion in the far field. Yes, a speaker swinging back and forth on a rope will evidence Doppler distortion because the low frequence swing does not couple to the air signifigantly. This means that the piston's position is never appropriate to the superimposed velocities and a Doppler shift that varies with the lower frequency velocity will occur. (I still believe the spectrum will have a flat top if it is emitting a single tone but that's another story.) A Doppler distortion will occur for any two frequencies that couple differently to the air but in the region of fairly flat transduction, there will be none. This is a bit more elaborate and may well contain error but I believe it is the case and accomodates all the cases of whistles and trains or little speakers moving in big ways. It does say, however, that the vernacular belief in Doppler distortion from a speaker due to components within its flat passband is simply wrong. Whatcha think? Bob -- "Things should be described as simply as possible, but no simpler." A. Einstein |
#312
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On 18 Aug 2004 19:47:02 -0700, (The Ghost)
wrote: Bob Cain wrote in message ... Why don't you consider actually contributing something of substance to this conversation? I know you are capable. I have, but you are too stupid to recognize it. ... to hammer your ... ----- http://mindspring.com/~benbradley |
#313
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On 18 Aug 2004 19:47:14 -0700, (The Ghost)
wrote: Bob Cain wrote in message ... Why don't you consider actually contributing something of substance to this conversation? I know you are capable. I have, but you are too stupid to recognize it. ... point home tonight, ... ----- http://mindspring.com/~benbradley |
#314
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On 18 Aug 2004 19:47:15 -0700, (The Ghost)
wrote: Bob Cain wrote in message ... Why don't you consider actually contributing something of substance to this conversation? I know you are capable. I have, but you are too stupid to recognize it. ... don't you? ----- Burma Shave, anyone? http://mindspring.com/~benbradley |
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The Ghost wrote: Bob Cain wrote in message ... Why don't you consider actually contributing something of substance to this conversation? I know you are capable. I have, but you are too stupid to recognize it. This must be Phil Allison using Gary Sokolich's handle. Careful, Phil, Gary is one nasty, sociopathic SOB and if he gets wind of this you are in real deap ****. He will stalk you until the end of your days. Bob -- "Things should be described as simply as possible, but no simpler." A. Einstein |
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"Arny Krueger" wrote in message
... That's because the train is not moving back and forth in front of us, in a periodic sine-shaped pattern. You OBVIOUSLY have not seen the trains in America! |
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Bob Cain wrote in message ...
Why don't you consider actually contributing something of substance to this conversation? I know you are capable. I have. The problem is that you are too stupid to recognize it. |
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"Phil Allison" wrote in message ... "Porky" Well, the cone is oscillating at the same frequency as the wave it's producing, but there's still the matter of the low velocity of the air molecules it's moving being converted to the high velocity soundwave that we hear. I think I see what you're saying though. ** Air molecules are never slow moving - their average speed is some 46 % greater than the speed of a sound wave. Not the point, because they are all moving at random, and if you set your thermostat to absolute zero, they don't move at all. General molecular motion is a function of temperature, and other than a small variation of the speed of sound with temperature it has little to do with this thread. My point was that the cone's velocity is a very small compared to the velocity of propagation of sound and the range of its excursion is very small compared to the wavelength of the tone it is producing . Thus a low velocity, small movement of the air in front of the cone is translated into a high velocity, long acoustic wave by a mechanism I know I don't need to explain to you because, with your IQ of 280, you grok it to the fullest instantly. |
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Bob Cain wrote in message ...
Why don't you consider actually contributing something of substance to this conversation? I know you are capable. I have, but you are too stupid to recognize it. |
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"William Sommerwerck" wrote in message ...
In terms of the question Bob Cain initially asked, the formula doesn't matter, because Doppler shift exists regardless of whether you're working in constant-velocity medium ("the luminiferous ether") or a non-constant-velocity medium (air). The formulas are different, but that doesn't have anything to do with the nature of the argument. Just to clarify my previous comments, I was referring to the velocity of the source, not the medium...........ie a constant velocity source such as a horn on a train vs a loudspeaker that is moving back and forth at a low frequency and simultaneously radiating a high frequency sound. |
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