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#121
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Jim Carr wrote: Here's a link that you tech folks can argue about: http://www.pcavtech.com/techtalk/doppler/ What's to argue? What it all means? Here's an observation based on intuition that I'd like someone to dispell. Since the high frequency component is supposed to be continuously oscilating in frequency between two extrema, why is the spectrum at its location in the FFT composed of peaks instead of a tabletop. Seems to me that all values of the frequencies between those extrema should show up and show up in equal amounts if the model everyone talks about is valid. Bob -- "Things should be described as simply as possible, but no simpler." A. Einstein |
#122
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"Bob Cain" wrote in message ... Jim Carr wrote: Here's a link that you tech folks can argue about: http://www.pcavtech.com/techtalk/doppler/ What's to argue? What it all means? Here's an observation based on intuition that I'd like someone to dispell. Since the high frequency component is supposed to be continuously oscilating in frequency between two extrema, why is the spectrum at its location in the FFT composed of peaks instead of a tabletop. Seems to me that all values of the frequencies between those extrema should show up and show up in equal amounts if the model everyone talks about is valid. I think you're right, Bob, that certainly seems logical to me. If it is Doppler distortion, the tone should be vary in a continuous warble from -50Hz to +50Hz because the woofer's velocity is continuously changing. |
#123
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"Porky" "Phil Allison" ** 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... ** Bob Cain is a not just a blatant troll, but a nut, a slanderer and a probably a desperate reject from the Flat Earth Society. What you are trying to pull on Porky is normally kept hidden from public view. BTW I found your post with the little test you did - it is full of dumb maths errors and wrong assertions. ............. Phil |
#124
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"Phil Allison" wrote in message ... "Porky" "Phil Allison" ** 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... ** Bob Cain is a not just a blatant troll, but a nut, a slanderer and a probably a desperate reject from the Flat Earth Society. What you are trying to pull on Porky is normally kept hidden from public view. BTW I found your post with the little test you did - it is full of dumb maths errors and wrong assertions. Phool, apparently you didn't know that Bob and I have known each other for quite some time. I have yet to see you post one technical fact, just smart ass remarks, and isn't that what trolls are known for. |
#125
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"Porky" wrote in message ... "Phil Allison" wrote in message ... "Porky" "Phil Allison" ** 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... ** Bob Cain is a not just a blatant troll, but a nut, a slanderer and a probably a desperate reject from the Flat Earth Society. What you are trying to pull on Porky is normally kept hidden from public view. BTW I found your post with the little test you did - it is full of dumb maths errors and wrong assertions. Phool, apparently you didn't know that Bob and I have known each other for quite some time. ** Now I do and it is hysterical. One troll and one dumb porker. I have yet to see you post one technical fact, ** You would not recognise one if it BIT you. That is what trolls an imbeciles are like. ............. Phil |
#126
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"Phil Allison" wrote in message ... Phool, apparently you didn't know that Bob and I have known each other for quite some time. ** Now I do and it is hysterical. One troll and one dumb porker. And one mentally retarded 14 year old! I have yet to see you post one technical fact, ** You would not recognise one if it BIT you. Try me, post one! That is what trolls an imbeciles are like. Indeed you are! |
#127
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"Porky" wrote in message
"Randy Yates" wrote in message ... Bob Cain writes: ruffrecords wrote: To produce FM there needs to be a non-linearity. If you detect FM there is a good chance a non-linearity exists. But it is not due to the doppler effect. Exactly, 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. 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! I think you've contrdicted yourself. A whistle riding on a train would be an example of a linear system if the motion of the train does not change the operational parameters of the whistle. 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. So far so good. Forget the train/whistle anology, it is not an accurate representation for what goes on with a speaker, period! But it is. A speaker generating a acostical signal that is received with Doppler distoriton is just as linear as that train whistle, and the Doppler distortion in either case has a common cause. This common cause is the relative motion of the source and the receiver. |
#128
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"Bob Cain" wrote in message
Randy Yates wrote: Proof by assertion? Sorry, Randy. I see nothing but proof by assertion from the supporters of "Doppler distortion." Even in the presence of experimental confirmation? 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. The predictive theory is as near as the nearest stack of JAES papers, which have been cited here a number of times. |
#129
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"Bob Cain" wrote in message
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? I do believe it is in Halliday and Resnick, even though it has been decades since I read it there. It's also in the JAES papers that have now been cited several times in the various discussions on the various newsgroups. |
#130
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"Porky" wrote in message
:-) 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! This close to being a first in the history of Usenet. I'm sure it has happened before, but I can't say where or when. Good stuff! |
#131
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"Bob Cain" wrote in message
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. GMAB. He cited Halliday and Resnick. I cited the JAES. Someone else cited the JAES. BTW Halliday and Resnick ride on: http://jws-edcv.wiley.com/college/bc...74____,00.html |
#132
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"Bob Cain" wrote in message
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. In many senses, I totally agree. However, Doppler distortion, while clearly agreeing with the formal definition of nonlinear distortion, is not related to any of the manifold other causes of nonlinear distortion in speakers. Those other forms of nonlinear distoriton are due to changes of speaker parameters, such as suspension compliance, as a function of the position of the cone. This is not debatable. Find a rigorous definition of linearity. I think I just posted one. I cheated, I picked it up from my www.pcavtech.com web site, I'm the author of record. But, its pretty orthodox and I can find a dozen others online that are about the same. For example: http://www.prosoundweb.com/install/s...rtion/dist.php "I was mistaken this afternoon in defining distortion broadly instead of nonlinear distortion. This latter gives rise to new frequencies not originally present and which cannot be restored." http://my.starstream.net/mk/Webpages...on_testing.htm "Non-linear distortion refers to the generation of different frequencies measured in a loudspeaker response that are not present in the original stimulus." http://www.daqarta.com/0diidist.htm "This results when two or more different frequency components interact within a nonlinear system. The output will then contain not only harmonics of the original frequencies, but also components at sum and difference frequencies that typically aren't harmonics of either input." I've presented it but it doesn't seem to have taken hold despite it being the bedrock of linear systems theory. There are in fact several different definitions of nonlinear distortion, some that focus on the cause (transfer function curvature) and some that focus on the effect (production of sounds not present in the input). In general they are very closely related. Either is fine with me, even though they don't mean identically the same. |
#133
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"Jim Carr" wrote in message
news:iygUc.9870$yh.2511@fed1read05 "Phil Allison" wrote in message ... ** The words of an ass. Can't you do any better than calling people names? Agreed. |
#134
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"Arny Krueger" "Jim Carr" "Phil Allison" ** The words of an ass. Can't you do any better than calling people names? Agreed. ** What happened to the context ???????????????????????? The remark was about the words posted. Arny is another ass. ............. Phil |
#135
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"Bob Cain" wrote in message
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. That could be both true and confusing, no? 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. This is a critcal point. **** you, and I say that with all due respect. The system here is everything from the face of the piston on out. Out how far? Until we get to the receiver, there is no Doppler distortion from that piston. Once we get to the receiver, there is Doppler distortion. But judged all by itself fixed in space, the receiver can be distortion-free. Nothing that occurs before that can be contributory and must be eliminated in some way from any experiment designed to catch Doppler at work. It would be nice to eliminate that, but in the real world of acoustic measurements... 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. Asked and answered, but it takes a little reading in standard references. Until that is done, "Doppler distortion" is not supported in theory. But it was all done 30 or more years ago, in the JAES. I sincerely hope no one will say that it isn't required because you see evidence of frequency modulation. Where else might that FM come from? 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. Except, that the driver does not evidence that nonlinearity unless the distance between the diaphragm and the receiver is varying. 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. At this point all sorts of things have been said. Me, I trust my experimental data, Halliday and Resnick, and the JAES. 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. So get thee to the library and study up! This is just basic science, folks. Sometimes you just got to do your reading. |
#136
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"Bob Cain" wrote in message
Arny Krueger wrote: If all the explanations for Doppler distortion are wrong, where does all of the FM we measure come from? Why does it correlate well with the *incorrect* theoretical predictions? What theoretical prediction might that be? I've yet to see a theory for "Doppler distortion" that predicts. Odd, that. Inability to obtain well-known, even classic references that have been formally cited, noted. |
#137
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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! Sorry, but it is. See my previous postings. 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. Doppler "distortion" is not the result of non-linear distortion. |
#138
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"Porky" wrote in message
I think you're right, Bob, that certainly seems logical to me. If it is Doppler distortion, the tone should be vary in a continuous warble from -50Hz to +50Hz because the woofer's velocity is continuously changing. The FFT plots are snapshots of a kind, but they are also time-exposures. 1 million points at 96 KHz is about 11 seconds worth of data. It is all averaged together in those pictures. If one uses a low enough modulating frequency, and a small enough sample set, snapshots with a faster effective exposure times result. One can then actually can see the carrier warbling. It will show up at different frequencies at different times in a sucession of snapshots. However, with a long exposure you see the results averaging of about 550 cycles of the 50 Hz tone. |
#139
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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? Any book on physics has a section on Doppler effects. There are two basic formulas -- one for which the velocity of the signal varies with the velocity of the observer (eg, sound) and one for which the velocity of the signal does not vary with the velocity of the observer (eg, light). It's a trivial matter to compute the velocity of a driver cone moving at a particular frequency and excursion. You can then easily compute the frequency shift of a HF signal being reproduced by the cone. I'm bothered by all this arguing, because I've repeatedly given clear, simple, non-mathematical explanations of what's going on. Yet there has been neither a consensus that they were correct, or a clear refutation of them. The purpose of "argument" is to arrive at the truth, not to stubbornly defend your present point of view. I can't believe I'm the only "intelligent" person in this group with any real insight into this issue. |
#140
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"William Sommerwerck" wrote in message
I can't believe I'm the only "intelligent" person in this group with any real insight into this issue. Thanks a lot, Bill. Not! |
#141
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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. The model you describe is a linear approximation of a nonlinear system. It works because the center is the *average* sound source position for a signal with no DC component. Once you start thinking about adding a DC bias, the model breaks down. As you've agreed, if the sound source is in motion, the system is no longer linear due to the speed at which sound travels in air, and can produce doppler distortion (for example, if I were to hold a speaker in my hands and run back and forth towards and away from you, there would be doppler, right?). Ok, so to show that the sound source is moving, we have to show two things: 1) that the sound source can change position. 2) that the sound source actually does change position while playing a sound. for #1, picture an ideal speaker surface. It has perfect frequency response all the way down to DC. If you put any waveform on its inputs, it follows it exactly, even if it's just a pure voltage. So if I put 3 volts on the speaker, say the surface moves forwards 3 feet. If I put -3 volts on the speaker, it moves backwards 6 feed to an absolute position (relative to its center position) of -3 feet. Now, while it's at -3 feet bias, I add a small sine wave to the signal. The voltage vibrates between -3.1 and -2.9 volts, and the speaker position, relatively to its neutral 0, vibrates around -3.1 and -2.9 feet. Would you still argue, in this case, that the sound is coming from the 0 foot position? If no, then you will agree that I have demonstrated that #1 is possible. If yes, then please explain how (make the speaker excursion 30 miles instead of 3 feet if you like). Now I will go for #2: Since I can set the speaker's position however I like by setting the DC bias, it follows that I can change that position while the high frequency sound is playing back on top of it. I could move it at say, 1 ft per second -- this speed is far too slow to produce a sound, and is practically DC. If you agree that I can set the position of the sound source by adjusting the DC bias, then it follows that I can *change* the position of the sound source by *changing* the DC bias. Any change in the position of the sound source is movement of the sound source (by the definitions of "movement" and "position"), and any movement of the sound source creates doppler distortion. QED. Furthermore, if moving the plate at 1ft per second creates doppler distortion, then moving at, say, 50 hz or whatever would also create it -- unless you can think of some arbitrary dividing line above which doppler distortion no longer occurs. Now, if you fall back on the "but the speaker is linear!" argument that you haven't let go of yet, then why don't *you* show the source, experiement, or mathematical derivation that proves that a speaker-air system is linear? This seems to be an assumption you're holding with absolutely *no* justification. Now, as for evidence that shows this occurs, I believe someone in this thread mentioned an article with measurements of doppler distortion. Of course, you've already dismissed any possible empirical evidence ahead of time by saying it's due to some non-linearity in the speaker itself and not doppler distortion. This shows a grave misunderstanding of how science works -- we can *never* proove 100% that something happens. We can only prove that things *don't* happen in certain ways. If the distortion measured fits the doppler model perfectly (and I'm pretty sure it does), then we're right to say that by current scientific knowledge, it's doppler distortion. If you'd like to hypothesize a new model for that measured distortion, or come up with an experiment to show that doppler distortion doesn't exist with a purely linear speaker, then go right ahead. Ken |
#142
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Nothing stupid about it. If both systems are linear then they will work in an identical manner. 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. Ken |
#143
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I can't believe I'm the only "intelligent" person in this group with
any real insight into this issue. Thanks a lot, Bill. Not! I don't remember you posting any elegant thought experiments, Arny. (If you did, and I overlooked them, I apologize.) |
#144
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Since I can set the speaker's position however I like by setting the
DC bias, it follows that I can change that position while the high frequency sound is playing back on top of it. I could move it at say, 1 ft per second -- this speed is far too slow to produce a sound, and is practically DC. If you agree that I can set the position of the sound source by adjusting the DC bias, then it follows that I can *change* the position of the sound source by *changing* the DC bias. Any change in the position of the sound source is movement of the sound source (by the definitions of "movement" and "position"), and any movement of the sound source creates doppler distortion. QED. This is basically correct reasoning. |
#145
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"William Sommerwerck" wrote in message
I can't believe I'm the only "intelligent" person in this group with any real insight into this issue. Thanks a lot, Bill. Not! I don't remember you posting any elegant thought experiments, Arny. (If you did, and I overlooked them, I apologize.) OK. BTW your thought experiments are generally just fine. I've posted my support for them at times, right? I find the whole situation quite instructive. Formal cites have been given, which can be resolved with a trip to any number of libraries. People argue on, regardless. In short, people seem to be a lot more enthusiastic about writing than reading. That seems to have the same effect as speaking instead of listening. I haven't seen anything correct that has posted on the audio groups of Usenet for days if not weeks, that the well-known scientific literature doesn't cover in spades. We're talking papers and books that are 30+ years old. It seems like I'm the only one in this group with ready access to the JAES which may be understandable. But Halliday and Resnick should be in a jillion different libraries. There don't seem to be a lot of people here who have actually taken first year college physics, it seems. |
#146
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On Tue, 17 Aug 2004 04:56:40 GMT, Randy Yates wrote:
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. That's not the problem here. Bob "believes in" Doppler theory when it's a whistle on a train. Bob refuses to see that the source of soud is the speaker cone, moved back and forth by the voice coil, thus the "source of sound" in a loudspeaker driver is moving. Bob claims and believes the sound source is a 'fixed source' relative to the driver's frame. I imagine this comes from multi-way loudspeaker system design, so that driver positions can be set relative to each other so that they are "phase coherent" or "time-aligned." (Off topic, both of these are probably registered trademarks of speaker makers from the '70's) This model is a good one and certainly works for this purpose, but like many models, it doesn't work for all situations. Specifically, it doesn't predict doppler distortion caused by cone excursion. 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? I suspect Bob knows it as well as you do, but he's just missing it and has some other idea in mind when it comes to a speaker cone. ----- http://mindspring.com/~benbradley |
#147
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"Ben Bradley" I suspect Bob knows it as well as you do, but he's just missing it and has some other idea in mind when it comes to a speaker cone. ** We are all the victims of a pathetic NG troll's wet dream and a hoax. Bob Cain has no interest in the facts - he is having a giant hoot at our expense. Only complete fools keep going when they are being conned. ............. Phil |
#148
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"ruffrecords" To produce FM there needs to be a non-linearity. Not really. A nonlinearity produces AM. Yes really. It is exactly how a mixer works in a receiver. The non linearity produces sum and difference frequencies. ** Which is characteristic of AM - you jerk. .......... Phil |
#149
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Bob Cain wrote:
Jim Carr wrote: Here's a link that you tech folks can argue about: http://www.pcavtech.com/techtalk/doppler/ What's to argue? What it all means? Here's an observation based on intuition that I'd like someone to dispell. Since the high frequency component is supposed to be continuously oscilating in frequency between two extrema, why is the spectrum at its location in the FFT composed of peaks instead of a tabletop. Seems to me that all values of the frequencies between those extrema should show up and show up in equal amounts if the model everyone talks about is valid. What is the lower limit of modulated frequency where doppler distortion would be observed? Why would there be one? Here's a thought, maybe the reductio-ad-absurdum argument: suppose the LF cone motion distorts the low frequency as well (ie, itself) if DD exists. IOW, *any* wave's shape would be warped by the doppler effect of a moving cone, even if it's only, say, the 20-Hz sine itself. This leads to at least two directions: 1. such distortion takes place everywhere (even on violin tops) and it's just how we hear it (Heisenberg), perhaps it's an inherent nonlinearity; or 2. no such thing happens and therefore DD does not exist. |
#150
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Arny Krueger wrote:
"ruffrecords" wrote in message Arny Krueger wrote: "ruffrecords" wrote in message PenguiN wrote: As far as our super-excursion speaker is concerned, the location that's generating the high pitched sound is moving forward and backward several feet. No it isn't. This is the flaw in all the doppler distortion arguments. If all the explanations for Doppler distortion are wrong, where does all of the FM we measure come from? Why does it correlate well with the *incorrect* theoretical predictions? To produce FM there needs to be a non-linearity. Not really. A nonlinearity produces AM. Yes really. It is exactly how a mixer works in a receiver. The non linearity produces sum and difference frequencies. Ian |
#151
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BTW your thought experiments are generally just fine.
I've posted my support for them at times, right? Right. And I saw them. I appreciate your support. (Though it was for the truth, as you saw it, and not for me. Which is as it should be.) I find the whole situation quite instructive. Formal cites have been given, which can be resolved with a trip to any number of libraries. People argue on, regardless. That's what I was griping about. The pro-Doppler explanations are almost certainly correct. But no one seems to be paying them much attention, or incisively refuting them. It's like explaining that something is impossible because it violates the law of energy conservation, but people keep arguing. In short, people seem to be a lot more enthusiastic about writing than reading. That seems to have the same effect as speaking instead of listening. Absatively. It seems like I'm the only one in this group with ready access to the JAES which may be understandable. But Halliday and Resnick should be in a jillion different libraries. Mine's somewhere in my library. There don't seem to be a lot of people here who have actually taken first year college physics, it seems. Or understood it. I have an above-Mensa IQ, but I had to take physics several times (ar, ar) before I really started "understanding" it. (Maybe.) |
#152
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Randy Yates wrote:
ruffrecords writes: If both systems are linear then they will work in an identical manner. That statement is absolutely correct, just as "If I am pregnant, then I am a female." is absolutely correct. And your point is what? Ian |
#153
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Bob Cain has no interest in the facts -- he is having a giant hoot
at our expense. I don't think so. It's rather that Bob is open-mined enough to ask for other people's opinions -- but when he gets a response that doesn't fit with his opinion, he doesn't want to accept it. We're all like that at one time or another. |
#154
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Porky wrote:
"Randy Yates" wrote in message ... Bob Cain writes: ruffrecords wrote: To produce FM there needs to be a non-linearity. If you detect FM there is a good chance a non-linearity exists. But it is not due to the doppler effect. Exactly, 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. 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! Precisely. Ian |
#155
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Randy Yates wrote:
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. No problem with that. The problem is which non-linearity in which bit of the system causes the sidebands the doppler boys have measured? Ian |
#156
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On Tue, 17 Aug 2004 08:38:04 -0700, so what wrote:
Bob Cain wrote: Jim Carr wrote: Here's a link that you tech folks can argue about: http://www.pcavtech.com/techtalk/doppler/ What's to argue? What it all means? Here's an observation based on intuition that I'd like someone to dispell. Since the high frequency component is supposed to be continuously oscilating in frequency between two extrema, why is the spectrum at its location in the FFT composed of peaks instead of a tabletop. Seems to me that all values of the frequencies between those extrema should show up and show up in equal amounts if the model everyone talks about is valid. What is the lower limit of modulated frequency where doppler distortion would be observed? Why would there be one? Here's a thought, maybe the reductio-ad-absurdum argument: suppose the LF cone motion distorts the low frequency as well (ie, itself) if DD exists. IOW, *any* wave's shape would be warped by the doppler effect of a moving cone, even if it's only, say, the 20-Hz sine itself. Yes, this happens. Take the head off an internal combustion engine so the piston is exposed. Have a separate motor run it. At lower speeds (3600RPM wil give a 60Hz output), it will give out a pretty good sine wave, as one would expect. A much higher speed will cause the piston to move at a substantial fraction of the speed of sound, and the wave will be distorted. This leads to at least two directions: 1. such distortion takes place everywhere (even on violin tops) and it's just how we hear it This is what I believe happens, but things such as violin tops move at such a small speed compared to the speed of sound that I suspect the doppler contribution is insignificant. The effects aren't that large with the large woofers described in these doppler threads. (Heisenberg), This has nothing to do with anything Heisenberg did, specfically not his principle of uncertainty in relation to subatomic particles, nor any analogy to it. perhaps it's an inherent nonlinearity; or 2. no such thing happens and therefore DD does not exist. ----- http://mindspring.com/~benbradley |
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Phil Allison wrote:
"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 Looks to me like Porky has moved up a few grades and phil is the new class idiot. (and I don't know if I can walk and chew gum because I hate the stuff). Ian |
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Jim Carr wrote:
Here's a link that you tech folks can argue about: http://www.pcavtech.com/techtalk/doppler/ Looks good to me. Plenty of evidence of harmonic distortion (casued by non-linearites and no evidence of 50Hz sidebands arounf the 4KHz signal. Doppler distortion is dead. Ian |
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"Picture the largest loudspeaker in the universe sitting outside"
"Now add to that signal a small, high pitched, low amplitude waveform" I couldn't of put it better myself. I was watching the argument and watching it turn into a slanging match. I wish that wouldn't happen. The only problem as far as I could see is that Porky was thinking of just a singular frequency, rather than a high frequency "riding" a low frequency. When that occurs, the train and whistle analogy indeed seems to make sense. With a singular frequency, IMHO, it does not. Cheers, Mark. -- PenguiN wrote: Picture the largest loudspeaker in the universe sitting outside somewhere. It's so big that it has a maximal excursion of several feet. Now picture a very low bass signal played on that speaker at almost maximal volume. The speaker cone is vibrating in-out-in-out-in-out. Now add to that signal a small, high pitched, low amplitude waveform. The two waveforms are added together so that it seems like the higher pitched wave is "riding on top of" the bass wave. As far as our super-excursion speaker is concerned, the location that's generating the high pitched sound is moving forward and backward several feet. |
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"Porky" wrote in message ...
"Bob Cain" wrote in message ... Jim Carr wrote: Here's a link that you tech folks can argue about: http://www.pcavtech.com/techtalk/doppler/ What's to argue? What it all means? Here's an observation based on intuition that I'd like someone to dispell. Since the high frequency component is supposed to be continuously oscilating in frequency between two extrema, why is the spectrum at its location in the FFT composed of peaks instead of a tabletop. Seems to me that all values of the frequencies between those extrema should show up and show up in equal amounts if the model everyone talks about is valid. I think you're right, Bob, that certainly seems logical to me. If it is Doppler distortion, the tone should be vary in a continuous warble from -50Hz to +50Hz because the woofer's velocity is continuously changing. Uhm, no. Frequency modulation does *not* produce a flat tabletop. http://www2.sfu.ca/sonic-studio/hand...odulation.html Perhaps you both should review your basic signals & systems course before continuing this discussion? Ken |
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