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#441
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In alt.music.home-studio,rec.audio.tech,rec.audio.pro, Bob Cain
wrote: Randy Yates wrote: This is in every physics book and dozens if not hundreds of web sites. To terminate this drivel, I'll type it in for you here. The perceived frequency, or Doppler frequency, fd, of a frequency f due to a relative velocity v between source and observer is given as fd = f*c/(c + v), Randy, that equation is only defined for a static v. So if you start changing v, the doppler effect stops until you leave v alone for a while? How does the doppler effect know to stop and start up again? Seriously (or you can answer the above question seriously if you like), do you have any reference for the equation being defined only for v being static? Bob ----- http://mindspring.com/~benbradley |
#442
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Ben Bradley wrote: In alt.music.home-studio,rec.audio.tech,rec.audio.pro, Bob Cain wrote: Randy Yates wrote: This is in every physics book and dozens if not hundreds of web sites. To terminate this drivel, I'll type it in for you here. The perceived frequency, or Doppler frequency, fd, of a frequency f due to a relative velocity v between source and observer is given as fd = f*c/(c + v), Randy, that equation is only defined for a static v. So if you start changing v, the doppler effect stops until you leave v alone for a while? How does the doppler effect know to stop and start up again? I didn't say it stops, it just isn't described by that formula any more. The Doppler effect doesn't know anything. It is just produced in differing amounts in different situations. Seriously (or you can answer the above question seriously if you like), do you have any reference for the equation being defined only for v being static? Not really. That's just the assumption wherever it is presented. As an example of why an expression that contains static values won't generally remain valid when simply substituting a dynamic one, consider a black box containing some arbitrary network of R, L anc C elements, distributed and lumped, linear and non-linear, which connect two inputs to one output. If we hold one of those inputs X constant and characterize the output by applying dynamic signals at input Y, then change the value of the X input to another constant value and again characterize the output, and repeat this with enough different values on the constant input we will, in general, be able to write down an expression that relates output to input under those conditions. If now instead of holding the input X constant we apply a time varying signal, will the characterization we developed describe what the output will do? Consider what would happen if there were a parallel RC in series with X before going elsewhere in the network. The expression given for Doppler shift is the consequence of keeping v constant and cannot be generalized to the dynamic case by substitution. In the general dynamic case it will be a whole lot more complicated and geometry dependant. Depending on the geometry it will only be approximated by the given expression even in the static case. It is really only generally valid for a point source emitter and receiver in an unbounded free space filled with nothing but air. Bob -- "Things should be described as simply as possible, but no simpler." A. Einstein |
#443
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Bob Cain wrote in message ...
fd = f*c/(c + v), Randy, that equation is only defined for a static v. You say that with such authority, but you most certainly don't have the authority required to make such a bold assertion. Can you provide a reference to the technical literature to support such a claim? The answer is no, because no such reference exists. The fact of the matter is that your assertion is nothing more than a personal belief, which you have accepted without questioning its validity. Had you looked into it, as I have, you would have discovered that the equation applies under both constant velocity and dynamic velocity conditions. You will find the derivation in Allan Pierce's book entitled "Acoustics: An Introduction to Its Physical Principles and Applications." In connection with the derivation, Allan Pierce states "The result holds regardless of the detailed time history of the trajectory. The Doppler-shifted frequency at a given time and position is affected only by the source's velocity and frequency at the instant of generation of the wavelet currently being received. The source does not have to be traveling with constant velocity or in a straight line for the equation to apply." Bob, I've said this many times before and I am going to say it again. Your level of ignorance never ceases to amaze me. |
#444
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The Ghost wrote: You will find the derivation in Allan Pierce's book entitled "Acoustics: An Introduction to Its Physical Principles and Applications." Thanks for the reference. Do you happen to know of one that derives this and which costs somewhat less that $200 used? Bob -- "Things should be described as simply as possible, but no simpler." A. Einstein |
#445
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On Sun, 22 Aug 2004 18:28:15 -0700, Bob Cain
wrote: The Ghost wrote: You will find the derivation in Allan Pierce's book entitled "Acoustics: An Introduction to Its Physical Principles and Applications." Thanks for the reference. Do you happen to know of one that derives this and which costs somewhat less that $200 used? I have no idea what a used copy of Allan's book costs, but new it's $39. Plus $5 shipping to US locations. $30 (plus shipping) if you can find an ASA member willing to buy it for you. |
#446
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"Bob Cain" wrote in message
... The Ghost wrote: You will find the derivation in Allan Pierce's book entitled "Acoustics: An Introduction to Its Physical Principles and Applications." Thanks for the reference. Do you happen to know of one that derives this and which costs somewhat less that $200 used? Try http://www.allbookstores.com. I saw that same price on Amazon myself. Apparently it can be had much cheaper. |
#447
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In article ,
Bob Cain wrote: The Ghost wrote: You will find the derivation in Allan Pierce's book entitled "Acoustics: An Introduction to Its Physical Principles and Applications." Thanks for the reference. Do you happen to know of one that derives this and which costs somewhat less that $200 used? Bob http://asa.aip.org/publications.html#pub05 -- Herb Singleton Sound & Vibration Measurements http://www.cross-spectrum.com |
#448
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Ken Plotkin wrote: On Sun, 22 Aug 2004 18:28:15 -0700, Bob Cain wrote: The Ghost wrote: You will find the derivation in Allan Pierce's book entitled "Acoustics: An Introduction to Its Physical Principles and Applications." Thanks for the reference. Do you happen to know of one that derives this and which costs somewhat less that $200 used? I have no idea what a used copy of Allan's book costs, but new it's $39. Plus $5 shipping to US locations. $30 (plus shipping) if you can find an ASA member willing to buy it for you. Hmmm, I went to Amazon: http://www.amazon.com/exec/obidos/AS...212126-4296736 and it shows no new purchase price (out of print) and only a used one at $193.81. I guess that's the wrong place to look, eh? If I can find it for $39, it's as good as on order. Bob -- "Things should be described as simply as possible, but no simpler." A. Einstein |
#449
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Jim Carr wrote: Try http://www.allbookstores.com. I saw that same price on Amazon myself. Apparently it can be had much cheaper. Yes. Found it cheaper through AllBookstores and now have it on order. At least I hope so. Seems unavailable most places and the one I'm trying (ClassBook) will let me know tomorrow of its availability The general unavailability might be the reasons for the incredible Amazon used price. Sokolich so seldom offers any information at all that I'm wondering if he doesn't know about an availability problem. Nah, now I'm getting as paranoid as he is. :-) Thanks, Bob -- "Things should be described as simply as possible, but no simpler." A. Einstein |
#450
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"Bob Cain" wrote in message
The Ghost wrote: You will find the derivation in Allan Pierce's book entitled "Acoustics: An Introduction to Its Physical Principles and Applications." Thanks for the reference. Do you happen to know of one that derives this and which costs somewhat less that $200 used? http://www.walmart.com/catalog/produ...28 2995418457 $35.10 http://www.audioxpress.com/bksprods/books/bkac2.htm price $52.95 |
#451
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On Sun, 22 Aug 2004 23:58:52 -0400, "Arny Krueger"
wrote: http://www.walmart.com/catalog/produ...28 2995418457 $35.10 Out of stock. http://www.audioxpress.com/bksprods/books/bkac2.htm price $52.95 Higher than list price. |
#452
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"Randy Yates" wrote in message ... Bob Cain writes: With all this sturm and drang no one has yet produced a mathematical expression for the sound pressure at some chosen distance from a velocity controled piston in a tube (to keep the situation as simple as possible) given a signal containing the sum of some chosen pair of frequencies at a chosen relative magnitude. Odd, that. Sounds simple enough. You know Bob, you are an irritating ****. This is in every physics book and dozens if not hundreds of web sites. To terminate this drivel, I'll type it in for you here. The perceived frequency, or Doppler frequency, fd, of a frequency f due to a relative velocity v between source and observer is given as fd = f*c/(c + v), where c is the speed of the medium (about 1100 ft/second for sound at reasonable temperatures at sea level). The instantaneous velocity v(t) of a speaker cone that is reproducing a sine wave A*sin(2*pi*fl*t) at frequency fl (f low) and at an excursion of A (meters, inches or whatever) is v(t) = A*2*pi*fl*cos(2*pi*fl*t). Put these two facts together and you get the dynamic doppler shift in a speaker: fd = f*c/(c + A*2*pi*fl*cos(2*pi*fl*t)). Of course units have to match, but that's up to the person applying this equation. Now what???? How come no one has replied to this logic (or illogic, as the case may be:-)): "Here's another way of looking at it, putting a sound wave through a hole in the wall can't produce Doppler shift, no matter how many tones are in the waveform, and a speaker is effectively an artificial hole in the wall, in that the effective sound source isn't the speaker any more than it is the hole in the wall. Does anyone here think that if you stretched a thin diaphragm over a hole in a soundproof wall and had a band playing behind it, the diaphragm would cause Doppler Distortion? The speaker, provided it isn't exceeding its linear limits, is effectively exactly the same thing for all practical purposes. Instead of being driven by the sound source in the other room, it's driven by the electrical equivalent of the sound source in the other room. Can any of you provide an explanation of how an acoustic wave driving a diaphragm and passing the soundwave through it is in any way different than the diaphragm being driven by a motor being supplied with the exact electrical analog of that acoustic wave? And by that I mean that the difference will be such that the electrically driven one will produce Doppler distortion while the acoustically driven one doesn't." It seems to me that it boils down to the above situation, if the diaphragm covering the hole in the wall driven directly by the acoustic wave in the other room doesn't produce Doppler shift, then the diaphragm being driven by the exactly equivalent electrical wave won't either. Since the diaphragm over the hole is moving exactly like the acoustic wave coming through the hole, I don't see how any form of Doppler shift could be introduced, as obviously, the hole itself won't introduce Doppler shift. Note, I'm referring only to Doppler shift, not the lowpass effect of the hole, the inertia of the diaphragms, etc, which may affect the sound, but will have absolutely nothing to do with Doppler shift. |
#453
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"Randy Yates" wrote in message ... Mark Simonetti writes: The distortions you are talking about in this thread are comparitively small, please correct me if I'm wrong. That being the case, I was basically stating that you often find people are not even bothered about the larger distortions from sub standard systems, and that I felt it is unfortunate. What are these "larger" distortions you are referring to? Seems to me, as I read someone else state here recently, that the typical high-end audio freak laments issues that are several orders of magnitude below something like Doppler distortion in speakers. Not that Doppler distortion is the largest problem facing sound reproduction, but comparitively, it seems to be much more worthy of our attention. If Doppler distortion actually exists in speakers...:-) |
#454
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Porky wrote: "Here's another way of looking at it, putting a sound wave through a hole in the wall can't produce Doppler shift, no matter how many tones are in the waveform, and a speaker is effectively an artificial hole in the wall, in that the effective sound source isn't the speaker any more than it is the hole in the wall. Does anyone here think that if you stretched a thin diaphragm over a hole in a soundproof wall and had a band playing behind it, the diaphragm would cause Doppler Distortion? I like that! It evokes the reciprocity argument I've used and that nobody seems to like, but in a different and more realistic configuration. Sorry, Mike, I've been too busy to give your prior presentation of this a good look (actually recording and producing some local talent, and I do mean talent.) So what's wrong with this, anyone? I realize that Gary Sokolich could dispel it in a moment, given his authority, but likely won't. Odd, that. It seems to me that it boils down to the above situation, if the diaphragm covering the hole in the wall driven directly by the acoustic wave in the other room doesn't produce Doppler shift, then the diaphragm being driven by the exactly equivalent electrical wave won't either. And if it does, someone please explain why. The only possible answer that I can think of is that it is physically impossible to generate something in the other room that isn't Doppler distorted. Is that what is believed? All sound, it seems then is Doppler distorted. Odd, that. :-) Bob -- "Things should be described as simply as possible, but no simpler." A. Einstein |
#455
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"Ken Plotkin" wrote in message
On Sun, 22 Aug 2004 23:58:52 -0400, "Arny Krueger" wrote: http://www.walmart.com/catalog/produ...28 2995418457 $35.10 Out of stock. http://www.audioxpress.com/bksprods/books/bkac2.htm price $52.95 Higher than list price. Do you want to get the book for an affordable price, or do you want to make a deal? This book exudes a strong odor of "out of print". That means that you look at $52.95, contemplate Amazon's ca. $200 asking price, and do what you've got to do. |
#456
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Do you want to get the book for an affordable price,
or do you want to make a deal? This book exudes a strong odor of "out of print". That means that you look at $52.95, contemplate Amazon's ca. $200 asking price, and do what you've got to do. Exactly! Borrow if from a library and photocopy it! |
#457
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"Porky" wrote in message
... other room. Can any of you provide an explanation of how an acoustic wave driving a diaphragm and passing the soundwave through it is in any way different than the diaphragm being driven by a motor being supplied with the exact electrical analog of that acoustic wave? In the case of a speaker electrical energy moves a coil which pushes and pulls a diaphragm in order to compress and rareify air in order to create a sound wave. In your example the energy from the sound wave hits the *molecules* of the diaphragm and passes through at whatever speed of sound is within that material. The energy passes through that material by hitting air molecules. It does not force the diaphragm to compress and rareify the air to create a sound wave. The former passes sound energy through. The latter creates it via a different mechanism. At least that's how this undeducated mope sees it. |
#458
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Can any of you provide an explanation of how an acoustic wave
driving a diaphragm and passing the sound wave through it is in any way different than the diaphragm being driven by a motor being supplied with the exact electrical analog of that acoustic wave? There is no difference (with one exception, given below). In the 1980 JAES article explaining the design and development of the QUAD ESL-63 speaker system, Peter Walker makes this point explicitly -- the sound impinging the diaphragm sets it in motion, and that motion, in turn, moves the air on the other side. Mechanical energy IS the energy of motion; it cannot magically "pass through" the diaphragm without moving it. The one difference is that a voice coil would drive the diaphragm at only one point. The ESL-63 is electrostatic, and therefore driven over most of its surface. My Stereophile article about the ESL-63 in the SCES report for the year in which it was introduced explains this in more detail. |
#459
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alt.sci.physics.acoustics removed, not sure that I have permission to
post the 'please don't crosspost over here' email I got. On Sun, 22 Aug 2004 20:43:41 -0700, Bob Cain wrote: Jim Carr wrote: Try http://www.allbookstores.com. I saw that same price on Amazon myself. Apparently it can be had much cheaper. Yes. Found it cheaper through AllBookstores and now have it on order. Which one? I see 1981 ed. for $47.95 and a 1989 ed. for $35. Clicking on that I get he http://www.allbookstores.com/book/compare/0883186128 where two of seven sites say it's not available. Who knows how many of the other have "NOS" or are sold out and the database entry not updated. At least I hope so. Seems unavailable most places and the one I'm trying (ClassBook) will let me know tomorrow of its availability The general unavailability might be the reasons for the incredible Amazon used price. I see three used copies through bookfinder.com, $95, $150 and $193. It definitely appears to be hard-to-find and in demand. Sokolich so seldom offers any information at all that I'm wondering if he doesn't know about an availability problem. Nah, now I'm getting as paranoid as he is. :-) Thanks, Bob ----- http://mindspring.com/~benbradley |
#460
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Porky wrote: If Doppler distortion actually exists in speakers...:-) It exists, not in speakers but in what follows. Bob -- "Things should be described as simply as possible, but no simpler." A. Einstein |
#461
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William Sommerwerck wrote: Can any of you provide an explanation of how an acoustic wave driving a diaphragm and passing the sound wave through it is in any way different than the diaphragm being driven by a motor being supplied with the exact electrical analog of that acoustic wave? There is no difference (with one exception, given below). In the 1980 JAES article explaining the design and development of the QUAD ESL-63 speaker system, Peter Walker makes this point explicitly -- the sound impinging the diaphragm sets it in motion, and that motion, in turn, moves the air on the other side. Mechanical energy IS the energy of motion; it cannot magically "pass through" the diaphragm without moving it. William, do you see that this argues against Doppler distortion being a phenomenon that occurs because of some wierd mixing at the piston/air interface which makes the motion that is imparted there intrinsically distorted? The ESL is a very good piston. Put one in a teminated tube, for example, and no Doppler distortion will be generated. Under conditions of a linear velocity/pressure relationship in the air, Doppler distortion is something that happens in the air gradually. Along any ray, it is developed as a function of the divergence of the frequency dependant coupling from equal and flat. In the limit of the actual piston/air interface it goes to zero. The one difference is that a voice coil would drive the diaphragm at only one point. The ESL-63 is electrostatic, and therefore driven over most of its surface. That's a big difference that is really important but not to Doppler distortion. Bob -- "Things should be described as simply as possible, but no simpler." A. Einstein |
#462
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Bob Cain wrote: Jim Carr wrote: Try http://www.allbookstores.com. I saw that same price on Amazon myself. Apparently it can be had much cheaper. Yes. Found it cheaper through AllBookstores and now have it on order. At least I hope so. Seems unavailable most places and the one I'm trying (ClassBook) will let me know tomorrow of its availability Unavailable. Will try ASA tomorrow. You too may be able to get upwards of $200 for your copy. :-) Bob -- "Things should be described as simply as possible, but no simpler." A. Einstein |
#463
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On Mon, 23 Aug 2004 07:25:43 -0400, "Arny Krueger"
wrote: Do you want to get the book for an affordable price, or do you want to make a deal? This book exudes a strong odor of "out of print". That means that you look at $52.95, contemplate Amazon's ca. $200 asking price, and do what you've got to do. I already have a copy, which I bought new for $25. As has been mentioned a couple of times, the book is available from ASA for $30 (members) or $39 (non-members) and a link was provided several posts back. Ken Plotkin |
#464
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Bob Cain writes:
Bob Cain wrote: Jim Carr wrote: Try http://www.allbookstores.com. I saw that same price on Amazon myself. Apparently it can be had much cheaper. Yes. Found it cheaper through AllBookstores and now have it on order. At least I hope so. Seems unavailable most places and the one I'm trying (ClassBook) will let me know tomorrow of its availability Unavailable. Will try ASA tomorrow. You too may be able to get upwards of $200 for your copy. :-) Sure makes it convenient for you to ignore information contradicting your beliefs, eh Bob? -- % Randy Yates % "Though you ride on the wheels of tomorrow, %% Fuquay-Varina, NC % you still wander the fields of your %%% 919-577-9882 % sorrow." %%%% % '21st Century Man', *Time*, ELO http://home.earthlink.net/~yatescr |
#465
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Randy Yates wrote: Bob Cain writes: Bob Cain wrote: Jim Carr wrote: Try http://www.allbookstores.com. I saw that same price on Amazon myself. Apparently it can be had much cheaper. Yes. Found it cheaper through AllBookstores and now have it on order. At least I hope so. Seems unavailable most places and the one I'm trying (ClassBook) will let me know tomorrow of its availability Unavailable. Will try ASA tomorrow. You too may be able to get upwards of $200 for your copy. :-) Sure makes it convenient for you to ignore information contradicting your beliefs, eh Bob? What the **** are you talking about? After finding several "sources" from which it was not available and a couple that said it was out of print, I ordered the book yesterday (used or new) from one that indicated availability and received the cancellation today. Tomorrow I call ASA to see if they have it because it was too late to call today when I got the cancellation. Make sure your mind is loaded before shooting off your ****ing mouth, cowboy. You're starting to **** me off and that isn't easy or fun for anyone. I'd really like to know what has made you so damned snarky and antagonsitic toward me. Is this the way you always handle technical disagreement? Seems you've been indulging in Sokolich's poison. Bob -- "Things should be described as simply as possible, but no simpler." A. Einstein |
#466
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On Mon, 23 Aug 2004 19:13:32 -0700, Bob Cain
wrote: [snip] I'd really like to know what has made you so damned snarky and antagonsitic toward me. Is this the way you always Bob, you seem to have a knack for drawing that out. handle technical disagreement? Seems you've been indulging in Sokolich's poison. Poison? I've enjoyed Gary's posts for quite a while. Technical content is as close to 100% as anyone ever gets - if you ever disagree with him, you've got to ask yourself what you're missing. His humor often has me rolling on the floor laughing. Yeah, discussing personalities is OT, but I'd hate to see Gary get tired of posting here. Ken Plotkin |
#467
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Ken Plotkin writes:
On Mon, 23 Aug 2004 19:13:32 -0700, Bob Cain wrote: [snip] I'd really like to know what has made you so damned snarky and antagonsitic toward me. Is this the way you always Bob, you seem to have a knack for drawing that out. handle technical disagreement? Seems you've been indulging in Sokolich's poison. Poison? I've enjoyed Gary's posts for quite a while. Technical content is as close to 100% as anyone ever gets - if you ever disagree with him, you've got to ask yourself what you're missing. His humor often has me rolling on the floor laughing. Yeah, discussing personalities is OT, but I'd hate to see Gary get tired of posting here. Thanks Ken, but my name is Randy! (: -- % Randy Yates % "Rollin' and riding and slippin' and %% Fuquay-Varina, NC % sliding, it's magic." %%% 919-577-9882 % %%%% % 'Living' Thing', *A New World Record*, ELO http://home.earthlink.net/~yatescr |
#468
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Wow. There *IS* blood flowing to his brain.
--RY Bob Cain writes: Randy Yates wrote: Bob Cain writes: Bob Cain wrote: Jim Carr wrote: Try http://www.allbookstores.com. I saw that same price on Amazon myself. Apparently it can be had much cheaper. Yes. Found it cheaper through AllBookstores and now have it on order. At least I hope so. Seems unavailable most places and the one I'm trying (ClassBook) will let me know tomorrow of its availability Unavailable. Will try ASA tomorrow. You too may be able to get upwards of $200 for your copy. :-) Sure makes it convenient for you to ignore information contradicting your beliefs, eh Bob? What the **** are you talking about? After finding several "sources" from which it was not available and a couple that said it was out of print, I ordered the book yesterday (used or new) from one that indicated availability and received the cancellation today. Tomorrow I call ASA to see if they have it because it was too late to call today when I got the cancellation. Make sure your mind is loaded before shooting off your ****ing mouth, cowboy. You're starting to **** me off and that isn't easy or fun for anyone. I'd really like to know what has made you so damned snarky and antagonsitic toward me. Is this the way you always handle technical disagreement? Seems you've been indulging in Sokolich's poison. Bob -- "Things should be described as simply as possible, but no simpler." A. Einstein -- % Randy Yates % "Though you ride on the wheels of tomorrow, %% Fuquay-Varina, NC % you still wander the fields of your %%% 919-577-9882 % sorrow." %%%% % '21st Century Man', *Time*, ELO http://home.earthlink.net/~yatescr |
#469
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PS: Bob, if it makes you feel any better, I'd have a beer
with you, no matter what you think about Doppler! I hope you can take this along the avenue of laughing at yourself. (Course it'd be different if we were laughing at me...) --RY Randy Yates writes: Wow. There *IS* blood flowing to his brain. --RY Bob Cain writes: Randy Yates wrote: Bob Cain writes: Bob Cain wrote: Jim Carr wrote: Try http://www.allbookstores.com. I saw that same price on Amazon myself. Apparently it can be had much cheaper. Yes. Found it cheaper through AllBookstores and now have it on order. At least I hope so. Seems unavailable most places and the one I'm trying (ClassBook) will let me know tomorrow of its availability Unavailable. Will try ASA tomorrow. You too may be able to get upwards of $200 for your copy. :-) Sure makes it convenient for you to ignore information contradicting your beliefs, eh Bob? What the **** are you talking about? After finding several "sources" from which it was not available and a couple that said it was out of print, I ordered the book yesterday (used or new) from one that indicated availability and received the cancellation today. Tomorrow I call ASA to see if they have it because it was too late to call today when I got the cancellation. Make sure your mind is loaded before shooting off your ****ing mouth, cowboy. You're starting to **** me off and that isn't easy or fun for anyone. I'd really like to know what has made you so damned snarky and antagonsitic toward me. Is this the way you always handle technical disagreement? Seems you've been indulging in Sokolich's poison. Bob -- "Things should be described as simply as possible, but no simpler." A. Einstein -- % Randy Yates % "Though you ride on the wheels of tomorrow, %% Fuquay-Varina, NC % you still wander the fields of your %%% 919-577-9882 % sorrow." %%%% % '21st Century Man', *Time*, ELO http://home.earthlink.net/~yatescr -- % Randy Yates % "Rollin' and riding and slippin' and %% Fuquay-Varina, NC % sliding, it's magic." %%% 919-577-9882 % %%%% % 'Living' Thing', *A New World Record*, ELO http://home.earthlink.net/~yatescr |
#470
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"The Ghost" wrote in message m... "Porky" wrote in message ... Methinks The Ghost has a compulsive need to repeat everything three times. Maybe he labors under the misapprehension that repeating a falsehood enough will make it true. Methinks Porky has pig fat for brains. ....And methinks The Ghost has protoplasmic porcine paskat for brains. (I had to resort to Finnish to keep the alliteration going:-)) BTW, no point in replying to this because you've been *plonked* |
#471
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"Jim Carr" wrote in message news:rOmWc.8997$L94.5165@fed1read07... "Porky" wrote in message ... other room. Can any of you provide an explanation of how an acoustic wave driving a diaphragm and passing the soundwave through it is in any way different than the diaphragm being driven by a motor being supplied with the exact electrical analog of that acoustic wave? In the case of a speaker electrical energy moves a coil which pushes and pulls a diaphragm in order to compress and rareify air in order to create a sound wave. In your example the energy from the sound wave hits the *molecules* of the diaphragm and passes through at whatever speed of sound is within that material. The energy passes through that material by hitting air molecules. It does not force the diaphragm to compress and rareify the air to create a sound wave. The former passes sound energy through. The latter creates it via a different mechanism. At least that's how this undeducated mope sees it. Jim, have you ever seen a speaker with a passive radiator? In fact the diphragm both is driven by the acoustic wave and allows some sound to pass through it, but what if the the diaphragm were soundproof" If it were low enough in mass, you'd still hear sound through it, and if it were massless, you'd hear all the sound. The question then becomes, does the diapragm generate Doppler distortion because it is driven by the acoustic wave, especially at the lower frequencies. |
#472
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"William Sommerwerck" wrote in message ... Can any of you provide an explanation of how an acoustic wave driving a diaphragm and passing the sound wave through it is in any way different than the diaphragm being driven by a motor being supplied with the exact electrical analog of that acoustic wave? There is no difference (with one exception, given below). In the 1980 JAES article explaining the design and development of the QUAD ESL-63 speaker system, Peter Walker makes this point explicitly -- the sound impinging the diaphragm sets it in motion, and that motion, in turn, moves the air on the other side. Mechanical energy IS the energy of motion; it cannot magically "pass through" the diaphragm without moving it. The one difference is that a voice coil would drive the diaphragm at only one point. The ESL-63 is electrostatic, and therefore driven over most of its surface. My Stereophile article about the ESL-63 in the SCES report for the year in which it was introduced explains this in more detail. I agree, and while that may be a source of distortion, it isnt Doppler distortion. |
#473
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"Bob Cain" wrote in message ... William Sommerwerck wrote: Can any of you provide an explanation of how an acoustic wave driving a diaphragm and passing the sound wave through it is in any way different than the diaphragm being driven by a motor being supplied with the exact electrical analog of that acoustic wave? There is no difference (with one exception, given below). In the 1980 JAES article explaining the design and development of the QUAD ESL-63 speaker system, Peter Walker makes this point explicitly -- the sound impinging the diaphragm sets it in motion, and that motion, in turn, moves the air on the other side. Mechanical energy IS the energy of motion; it cannot magically "pass through" the diaphragm without moving it. William, do you see that this argues against Doppler distortion being a phenomenon that occurs because of some wierd mixing at the piston/air interface which makes the motion that is imparted there intrinsically distorted? The ESL is a very good piston. Put one in a teminated tube, for example, and no Doppler distortion will be generated. Under conditions of a linear velocity/pressure relationship in the air, Doppler distortion is something that happens in the air gradually. Along any ray, it is developed as a function of the divergence of the frequency dependant coupling from equal and flat. In the limit of the actual piston/air interface it goes to zero. The one difference is that a voice coil would drive the diaphragm at only one point. The ESL-63 is electrostatic, and therefore driven over most of its surface. That's a big difference that is really important but not to Doppler distortion. Bob, I think the big guns have gone back to the drawing board for this one. The "hole in the wall" analogy is elegantly simple, but the math behind it isn't, especially if one is trying to come up with an equation that shows that Doppler distortion will result. I'm still not absolutely sure I might not be missing something, but if I am, I think we can rest assured that someone will call me on it. I don't mind, this discussion has given me some much needed mental exercise, and I've enjoyed it!:-) |
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Porky wrote: Jim, have you ever seen a speaker with a passive radiator? In fact the diphragm both is driven by the acoustic wave and allows some sound to pass through it, but what if the the diaphragm were soundproof" If it were low enough in mass, you'd still hear sound through it, and if it were massless, you'd hear all the sound. The question then becomes, does the diapragm generate Doppler distortion because it is driven by the acoustic wave, especially at the lower frequencies. Hey, another good one! Bob -- "Things should be described as simply as possible, but no simpler." A. Einstein |
#475
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"Bob Cain" wrote in message
... Porky wrote: Jim, have you ever seen a speaker with a passive radiator? In fact the diphragm both is driven by the acoustic wave and allows some sound to pass through it, but what if the the diaphragm were soundproof" If it were low enough in mass, you'd still hear sound through it, and if it were massless, you'd hear all the sound. The question then becomes, does the diapragm generate Doppler distortion because it is driven by the acoustic wave, especially at the lower frequencies. Hey, another good one! If you accept Doppler "distortion" as described by others, then instruments producing multiple tones has the problem. Hit two keys on the piano and the wood vibrates for both sounds. What a freaking miss! Thank God my ears are not trained enough to hear it! |
#476
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On Tue, 24 Aug 2004 19:48:42 -0700, "Jim Carr"
wrote: "Bob Cain" wrote in message ... Porky wrote: Jim, have you ever seen a speaker with a passive radiator? In fact the diphragm both is driven by the acoustic wave and allows some sound to pass through it, but what if the the diaphragm were soundproof" If it were low enough in mass, you'd still hear sound through it, and if it were massless, you'd hear all the sound. The question then becomes, does the diapragm generate Doppler distortion because it is driven by the acoustic wave, especially at the lower frequencies. Hey, another good one! Actually, it would seem that the diaphragm should do the 'reciprocity' thing you were talking about earlier, and not change the sound. If you accept Doppler "distortion" as described by others, then instruments producing multiple tones has the problem. Hit two keys on the piano and the wood vibrates for both sounds. Yes, it's true, but the piano (and almost all instruments') soundboard moves a very small amount (the soundboard's large surface area makes up for the small movement and gives the instrument decent volume), and so the doppler effect/distortion generated is insignificant. What a freaking miss! Do you mean mess, or is there some lady involved whom I haven't heard about? Thank God my ears are not trained enough to hear it! ----- http://mindspring.com/~benbradley |
#477
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Porky wrote:
"Bob Cain" wrote in message ... William Sommerwerck wrote: Can any of you provide an explanation of how an acoustic wave driving a diaphragm and passing the sound wave through it is in any way different than the diaphragm being driven by a motor being supplied with the exact electrical analog of that acoustic wave? There is no difference (with one exception, given below). Bob, I think the big guns have gone back to the drawing board for this one. The "hole in the wall" analogy is elegantly simple, but the math behind it isn't, especially if one is trying to come up with an equation that shows that Doppler distortion will result. I'm still not absolutely sure I might not be missing something, but if I am, I think we can rest assured that someone will call me on it. I don't mind, this discussion has given me some much needed mental exercise, and I've enjoyed it!:-) What becomes sound does not doppler-shift. What does not, becomes shifted. Neither a moving train nor a moving star impart their motion to the medium, only the sound or light is transmitted. And shifted. But they don't drag the universe along with them. An operating speaker cone moves the air; the air has no motion relative to the cone (ignoring losses), whether the freq is high or low. That is, until the note's too low or you swing it on a rope. So the degree of coupling at each frequency must become a factor in the equations. |
#478
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"Jim Carr" wrote in message news:t3TWc.21701$L94.6656@fed1read07... "Bob Cain" wrote in message ... Porky wrote: Jim, have you ever seen a speaker with a passive radiator? In fact the diphragm both is driven by the acoustic wave and allows some sound to pass through it, but what if the the diaphragm were soundproof" If it were low enough in mass, you'd still hear sound through it, and if it were massless, you'd hear all the sound. The question then becomes, does the diapragm generate Doppler distortion because it is driven by the acoustic wave, especially at the lower frequencies. Hey, another good one! If you accept Doppler "distortion" as described by others, then instruments producing multiple tones has the problem. Hit two keys on the piano and the wood vibrates for both sounds. What a freaking miss! Thank God my ears are not trained enough to hear it! My position (I think!:-)) is that any thing, be it speaker, instrument, etc, that produces a complex waveform as a gestalt doesn't introduce Doppler distortion because the sound wave is created as a single complex entity. If a speaker produces Doppler shift, then a guitar or piano string, or any other musical instrument or portion thereof which vibrates and whose individual notes have high frequency components (i.e. they aren't pure sinewave tones, which would include almost all musical instruments that have anything that vibrates as a soundsource) would also produce Doppler shift with every individual note as well as with combinations of notes played, and if this were the case then Doppler shift would be a part of the natural order of things musical, and Doppler shift could thus be entirely disregarded as a source of "distortion", period! I think this should pretty much drive the final nail in the Doppler distortion issue's coffin, because if speakers introduce Doppler shift then so does everything else which vibrates to produce sound. I still don't think Doppler shift is introduced by speakers opperating under normal conditions, but if it is, it's a part of the natural order and not distortion at all!:-) |
#479
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S O'Neill wrote: So the degree of coupling at each frequency must become a factor in the equations. And by my study of this to date, the only one. I won't try and fool anyone that a full, predictive theory based on this principle has been worked out but I believe it can and will predict all Doppler distortion that is measured. With the time I have available it will be slow in coming from me but you can be sure I'll be putting some effort into it. Of course, I highly encourage anyone who thinks the principle has merit to beat me to it. :-) I think two sets of boundry conditions would be most useful for a first development, the piston in an infinite baffle and the free standing piston. The piston in a box might be approachable too but then a whole lot of other conditions enter the picture. It will be found that the effect is a function of distance from the piston and the angle made to its axis, becoming zero at the limit of the piston/air interface where the "other" principle says it occurs. A final theory would predict the result given any forcing function of the piston, but an intermediate one that just focused on two superimposed tones would be illustrative and testable. In the mean time I also encourage anyone to develop a predictive theory from the "other" principle. If that's possible, may the two eventually meet in the arena of experiment. Over, and at last, out 'till then, Bob -- "Things should be described as simply as possible, but no simpler." A. Einstein |
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"Ben Bradley" wrote in message
... What a freaking miss! Do you mean mess, or is there some lady involved whom I haven't heard about? Oh, I meant miss alright. Christian Doppler's youngest daughter, Wilda. When Doppler's wife left him and took their daughter, they rode away on a train. His daughter was screaming the whole time. It was then that he noticed the pitch seemingly change. Over the years people assumed he meant whistle, not Wilda. |
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