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#321
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"Phil Allison" wrote in message ... "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 ??? Wrong, Phool, my IQ is a bit over 140 to a bit over 150, depending on the IQ test used. Modest being that I am, I use the lower figure. Yes, I am artistic, I am a musician and I paint on occasion, and I just love your southern drawl. Unlike you, I am always learning, period, and also unlike you, I have the wisdom to learn and benefit from my mistakes. BTW, I can sing, I just have a lousy voice and there is nothing I can do about it. |
#322
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"Jim Carr" wrote in message news:1gVUc.10087$yh.1675@fed1read05... "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! Yeah, we have AMtrack, not FMtrack.... |
#323
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"Bob Cain" wrote in message ... 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? If you mean that a whistle riding on a moving train, or a speaker swinging back and forth (or spinning round and round like in a Leslie speaker system) in a repeating oscillation cycle will produce Doppler shift, but a stationary speaker reproducing a complex waveform containing a mixed LF and HF tone (or any multiple combination of tones, as would be the case in a complex musical waveform) won't produce Doppler shift, then, by golly, I think you're right! |
#324
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"Porky" "Phil Allison" ** Wrong direction Porker - yours is only about 85. Plus you are autistic. Learning to sing yet ??? Wrong, Phool, my IQ is a bit over 140 to a bit over 150, depending on the IQ test used. Modest being that I am, I use the lower figure. Yes, I am artistic, I am a musician and I paint on occasion, and I just love your southern drawl. ** The word was "'autistic" - which proves my point. ........... Phil |
#325
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"Phil Allison" wrote in message ... "Porky" "Phil Allison" ** Wrong direction Porker - yours is only about 85. Plus you are autistic. Learning to sing yet ??? Wrong, Phool, my IQ is a bit over 140 to a bit over 150, depending on the IQ test used. Modest being that I am, I use the lower figure. Yes, I am artistic, I am a musician and I paint on occasion, and I just love your southern drawl. ** The word was "'autistic" - which proves my point. Ahhh, "autistic": "A psychiatric disorder of childhood characterized by marked deficits in communication and social interaction, preoccupation with fantasy, language impairment, and abnormal behavior, such as repetitive acts and excessive attachment to certain objects. It is usually associated with intellectual impairment." Yes, it describes your behavior here quite well. I think you hit the nail on the head with your self-diagnosis! |
#326
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"Porky" writes:
"Jim Carr" wrote in message news:1gVUc.10087$yh.1675@fed1read05... "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! Yeah, we have AMtrack, not FMtrack.... Ba-domp - bom! play horn notes here -- % Randy Yates % "Ticket to the moon, flight leaves here today %% Fuquay-Varina, NC % from Satellite 2" %%% 919-577-9882 % 'Ticket To The Moon' %%%% % *Time*, Electric Light Orchestra http://home.earthlink.net/~yatescr |
#327
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Mike, you are just feeding this troll and it doesn't compliment you. I suggest you plonk him as I and about everyone else has. Bob -- "Things should be described as simply as possible, but no simpler." A. Einstein |
#328
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Porky wrote: "Jim Carr" wrote in message news:1gVUc.10087$yh.1675@fed1read05... "Arny Krueger" wrote in message ... That's because the train is not moving back and forth in front of us, in a periodic sine-shaped pattern. You OBVIOUSLY have not seen the trains in America! Yeah, we have AMtrack, not FMtrack.... Ouch! :-) Bob -- "Things should be described as simply as possible, but no simpler." A. Einstein |
#329
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Porky wrote: If you mean that a whistle riding on a moving train, or a speaker swinging back and forth (or spinning round and round like in a Leslie speaker system) in a repeating oscillation cycle will produce Doppler shift, but a stationary speaker reproducing a complex waveform containing a mixed LF and HF tone (or any multiple combination of tones, as would be the case in a complex musical waveform) won't produce Doppler shift, then, by golly, I think you're right! I even finally agree that in many cases it has the properties that can be called Doppler distortion, so it is a real phenomenon in qualified conditions but not for the reasons usually given and not from the systems for which it has been claimed. Bob -- "Things should be described as simply as possible, but no simpler." A. Einstein |
#330
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"Bob Cain" wrote in message ... Mike, you are just feeding this troll and it doesn't compliment you. I suggest you plonk him as I and about everyone else has. I have to reluctantly agree with you, but it is fun to one-up him every time he throws an insult. However, this guy is so easy, it isn't even a decent mental exercise, so I'll just send him to ignore-hell. |
#331
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"Bob Cain" wrote in message ... Porky wrote: "Jim Carr" wrote in message news:1gVUc.10087$yh.1675@fed1read05... "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! Yeah, we have AMtrack, not FMtrack.... Ouch! :-) Actually, I have to give Jim credit for that one, it isn't often that one gets handed a straight line that tempting... |
#332
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"Porky" Mike, you are just feeding this troll and it doesn't compliment you. I suggest you plonk him as I and about everyone else has. I have to reluctantly agree with you, but it is fun to one-up him every time he throws an insult. ** Only in your wet dreams - you pathetic fat arsed imbecile. You are Bob are the most blatant of trolls. Posting such utter ****e as you two have in a pubic forum should punishable at law. ............. Phil |
#333
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"Bob Cain" wrote in message ... Porky wrote: If you mean that a whistle riding on a moving train, or a speaker swinging back and forth (or spinning round and round like in a Leslie speaker system) in a repeating oscillation cycle will produce Doppler shift, but a stationary speaker reproducing a complex waveform containing a mixed LF and HF tone (or any multiple combination of tones, as would be the case in a complex musical waveform) won't produce Doppler shift, then, by golly, I think you're right! I even finally agree that in many cases it has the properties that can be called Doppler distortion, so it is a real phenomenon in qualified conditions but not for the reasons usually given and not from the systems for which it has been claimed. I would go so far as to say that anything generating sound and in motion relative to the listener will generate Doppler shift, but in the special case of a speaker reproducing a complex waveform consisting of more than one pure tone, the velocity of the source relative to the listener is effectively zero, and therefore no Doppler shift will be generated, because: 1) there is one complex waveform driving the speaker and producing the energy necessary to generate the sound, not some higher frequency or frequencies "riding" on some lower frequency. 2) the effective sound source is not the speaker cone, but some point or plane which does not move relative to the listener. The moving speaker cone just provides the mechanical energy which is transformed into acoustical energy by it's interaction with the surrounding air. Each instantaneous point in the complex motion of the cone is in direct co-relation to the corresponding instantaneous point of compression or rarefaction in the complex waveform and the notion that the source has motion relative to the listener is an illusion. The sound wave can be pictured as standing still with each bit coming into existance as the cone passes through that space. The sound wave might be represented as: -- - - -- - - -- with the space between the dots representing compression and rarefaction of the wave, and the cone's motion producing the sound can be represented as: ]-- - - -- - - -- ]- - - -- - - -- ] - - -- - - -- ]- - - -- - - -- ]-- - - -- - - -- ]- - - -- - - -- ] - - -- - - -- ]- - - -- - - -- Note that while the cone is moving, the apparent source is not moving, and this applies no matter how complex the waveform is. This can actually be measured with a sensitive pressure meter and graphed, showing that this is really what is happening. 3) the effective sum of all velocities is zero relative to the listener 4) due to the nature of how a speaker produces sound, the listener is effectively "riding on the train" 5) In order to produce Doppler shift, there must be a sound source in motion relative to the listener and in the case of a stationary speaker there is a complex sound source, but no motion relative to the listener 6) If a speaker did generate Doppler distortion, simply turning it so that the listener was looking at the edge of the speaker would eliminate the motion toward and away from the listener (the cone would move side to side, but would stay at a constant distance from the listener), and thus would eliminate Doppler distortion. I don't believe that this is the case in the real world. 7) the empirical measurements I made indicated that there was no audible or measurable Doppler shift when the Doppler equations predicted that there would be audible and measurable shift, therefore the Doppler equations do not apply to this special case. 8) I just have a gut feeling about it 9) none of the above or 10) any of the above Personally, I prefer number two. |
#334
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Porky wrote: I would go so far as to say that anything generating sound and in motion relative to the listener will generate Doppler shift, but in the special case of a speaker reproducing a complex waveform consisting of more than one pure tone, the velocity of the source relative to the listener is effectively zero, and therefore no Doppler shift will be generated, because: Tell me if this is equivalent or not: There is Doppler type mixing between two frequencies if and only if the pressure in the far field due to them is a different function of the velocity of the piston. Where the transfer function is flat in the Fourier sense, nothing mixes. That is what it all boils down to in the end. That is not at all the same as the standard argument because it won't happen in a tube and the standard argument says it will. Also, a single tone cannot produce Doppler distortion so I am definitely wrong about that. Yikes! I see why. The definition I've been bandying about for a linear system is actually the definiton of a linear, time invariant system. The system we are considering must be time variant in terms of the impedences involved. This is getting wierd. Can this yield what I've been asking for, a general expression for far field pressure as a function of piston velocity that includes the Doppler distortion? I'm not sure yet, but I'll be thinking about it. It is straightforward for any two frequencies, however, and is left as an exercise for the student. :-) Bob -- "Things should be described as simply as possible, but no simpler." A. Einstein |
#335
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"Porky" wrote in message
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? right. However, its a lot harder to properly measure doppler when the LF tone has a very low frequency. To measure it with a FFT you must use a FFT size that covers at least one cycle, and hopefully several cycles of the process. If the LF tone is 0.1 Hz, this means an absolute minimum of 10 seconds of data, and ideally 30 or more. At 44,100 Hz sampling, this would be a FFT composed of a minimum of 441,000 samples, and preferably several million samples. Consider the original example - the LF tone was 50 Hz. It had an 882 sample period. Note how much overkill there was when analyzed using a 65k sample FFT, or as I used a one million point FFT. |
#336
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"Jim Carr" wrote in message
news:1gVUc.10087$yh.1675@fed1read05 "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! LOL! There's a crossing I frequent north of here that must have a lot of trains doing switching, that seem to specialize in repetitive, back-and-forth movements. |
#337
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"Arny Krueger" wrote in message ... "Porky" wrote in message 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? right. However, its a lot harder to properly measure doppler when the LF tone has a very low frequency. To measure it with a FFT you must use a FFT size that covers at least one cycle, and hopefully several cycles of the process. If the LF tone is 0.1 Hz, this means an absolute minimum of 10 seconds of data, and ideally 30 or more. At 44,100 Hz sampling, this would be a FFT composed of a minimum of 441,000 samples, and preferably several million samples. Consider the original example - the LF tone was 50 Hz. It had an 882 sample period. Note how much overkill there was when analyzed using a 65k sample FFT, or as I used a one million point FFT. One of the problems with FFT analysis that we've all overlooked is that we aren't really dealing with analog waveforms in our simulations, and we can get erroneous results when using high FFT numbers because we start playing in the digital "cracks", so to speak, Having done a bit of experimentation, I've found that I get the most consistant results across the whole range be using an FFT number of 16K or 32K, higher rates give false results, especially at higher frequency HF tones. Alternatively, if your equipment will handle it, try creating the wave models at 24 or 32/96, or even 32/192, you'll see a considerable difference in your resluts, especailly at higher HF tones and FFT numbers, and your results will be more consistant across the entire range of LF and HF tones. |
#338
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"Bob Cain" wrote in message ... Porky wrote: I would go so far as to say that anything generating sound and in motion relative to the listener will generate Doppler shift, but in the special case of a speaker reproducing a complex waveform consisting of more than one pure tone, the velocity of the source relative to the listener is effectively zero, and therefore no Doppler shift will be generated, because: Tell me if this is equivalent or not: There is Doppler type mixing between two frequencies if and only if the pressure in the far field due to them is a different function of the velocity of the piston. Where the transfer function is flat in the Fourier sense, nothing mixes. That is what it all boils down to in the end. That is not at all the same as the standard argument because it won't happen in a tube and the standard argument says it will. Correct, for the simple reason that a speaker reproducing a complex waveform does so coherently, however, if you add another force vector such as moving the speaker, Doppler shift will occur in the entire reproduced sound, not just the HF component, this is how a Leslie speaker system works. Also, a single tone cannot produce Doppler distortion so I am definitely wrong about that. Yikes! I see why. The definition I've been bandying about for a linear system is actually the definiton of a linear, time invariant system. The system we are considering must be time variant in terms of the impedences involved. This is getting wierd. Can this yield what I've been asking for, a general expression for far field pressure as a function of piston velocity that includes the Doppler distortion? I'm not sure yet, but I'll be thinking about it. It is straightforward for any two frequencies, however, and is left as an exercise for the student. :-) It's just as straightforward for a complex musical waveform, you don't hear any Doppler shift unless you start moving the speaker. Here's another way to look at it, there is no Doppler shift in a speaker because the speaker is not the source of the sound, the air it compresses and rarifies is the actual sound source, and since moving air can't cause Doppler distortion (try having a friend whistle a steady tone in a variable gusty wind if you doubt it), there is no Doppler distortion introduced by a speaker. |
#339
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"Porky" Here's another way to look at it, there is no Doppler shift in a speaker because the speaker is not the source of the sound, the air it compresses and rarifies is the actual sound source, and since moving air can't cause Doppler distortion (try having a friend whistle a steady tone in a variable gusty wind if you doubt it), there is no Doppler distortion introduced by a speaker. ** Hey - Porky boy. If pig ignorant, asinine, hee- haw stupidity was an Olympic event - YOU would be the world record holder. Dumbness is YOUR forte - you excel at it in every way. You and Bob Cain should be the USA team for the " Synchronised Imbeciles " event. Just like synchronised diving - but he pool is empty !!!!!!!!!!! ............... Phil |
#340
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high frequency with a low frequency and applies that complex electrical
waveform to the speaker voice voil. The result is NOT a high frequency tone riding on a low frequency tone, it's a single complex waveform containing elements of both tones, and thus there is no Doppler distortion. That doesn't make sense. To generate a frequency, the speaker has to move back and forth at a certain rate. The higher the frequency, the faster the rate at which it moves. Surely if we want to hear both frequencies at once, the speaker has to vibrate at both speeds at once ? If you look at a low frequency sine wave with an amplitude against time graph, and SUM a much higher frequency much lower amplitude wave to it, surely you'll see the original low frequency sine wave, but the line itself instead of being a smooth sine wave, will be oscillating at the high frequency. This is what I imagine would happen anyway, I'm not near anything I can test this with right now. Just looking at what the line is doing will then surely tell you what the speaker is doing ? Surely it'll be following the wave ? So, the speaker would be slowly moving back and forth, following the amplitude of the low frequency signal, but as it moves back a forth, it'll be oscillating a small amount back and forth at its current position in the low frequency wave because that is what the input signal is doing. IMHO at least .... Here is an example; Our keyboard player once made his keyboard output such a low frequency signal, that you could watch the speaker slowly move back a forth quiet far, perhaps once every second. Are you telling me that, if I "mixed" a high frequency with that signal, the speaker would be no longer moving back and forth slowly about once per second ? -- Mark Simonetti. Freelance Software Engineer. |
#341
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"Porky" wrote in message
"Arny Krueger" wrote in message ... "Porky" wrote in message 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? right. However, its a lot harder to properly measure doppler when the LF tone has a very low frequency. To measure it with a FFT you must use a FFT size that covers at least one cycle, and hopefully several cycles of the process. If the LF tone is 0.1 Hz, this means an absolute minimum of 10 seconds of data, and ideally 30 or more. At 44,100 Hz sampling, this would be a FFT composed of a minimum of 441,000 samples, and preferably several million samples. Consider the original example - the LF tone was 50 Hz. It had an 882 sample period. Note how much overkill there was when analyzed using a 65k sample FFT, or as I used a one million point FFT. One of the problems with FFT analysis that we've all overlooked is that we aren't really dealing with analog waveforms in our simulations, and we can get erroneous results when using high FFT numbers because we start playing in the digital "cracks", so to speak, I'd like to see a believable fuirther explantion of that. FFT and I are going on our 42nd year, and we've been pretty good friends the whole time. Having done a bit of experimentation, I've found that I get the most consistent results across the whole range be using an FFT number of 16K or 32K, higher rates give false results, especially at higher frequency HF tones. I'd like to see a believable further explanation of that. Alternatively, if your equipment will handle it, try creating the wave models at 24 or 32/96, or even 32/192, you'll see a considerable difference in your results, especially at higher HF tones and FFT numbers, and your results will be more consistent across the entire range of LF and HF tones. I'd also like to see a believable further explanation of that. |
#342
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"Mark Simonetti" wrote in message
high frequency with a low frequency and applies that complex electrical waveform to the speaker voice voil. The result is NOT a high frequency tone riding on a low frequency tone, it's a single complex waveform containing elements of both tones, and thus there is no Doppler distortion. That doesn't make sense. To generate a frequency, the speaker has to move back and forth at a certain rate. The higher the frequency, the faster the rate at which it moves. Surely if we want to hear both frequencies at once, the speaker has to vibrate at both speeds at once ? The speaker is one entity, so it has only one speed at a time. In your case the speaker's speed is the sum of the two speeds. You later talk like you believe this. So why not say it up front? If you look at a low frequency sine wave with an amplitude against time graph, and SUM a much higher frequency much lower amplitude wave to it, surely you'll see the original low frequency sine wave, but the line itself instead of being a smooth sine wave, will be oscillating at the high frequency. Agreed This is what I imagine would happen anyway, I'm not near anything I can test this with right now. Just looking at what the line is doing will then surely tell you what the speaker is doing ? Surely it'll be following the wave ? Pretty much. So, the speaker would be slowly moving back and forth, following the amplitude of the low frequency signal, but as it moves back a forth, it'll be oscillating a small amount back and forth at its current position in the low frequency wave because that is what the input signal is doing. Ironcially, the velocity due to the lower frequency may be the greater of the two velocities that are summed together. IMHO at least .... Here is an example; Our keyboard player once made his keyboard output such a low frequency signal, that you could watch the speaker slowly move back a forth quiet far, perhaps once every second. Are you telling me that, if I "mixed" a high frequency with that signal, the speaker would be no longer moving back and forth slowly about once per second ? Of course it will. And its instanteious velocity is added to the instantaneous velocity due to the upper note. |
#343
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Arny Krueger wrote:
"Porky" wrote in message Having done a bit of experimentation, I've found that I get the most consistent results across the whole range be using an FFT number of 16K or 32K, higher rates give false results, especially at higher frequency HF tones. I'd like to see a believable further explanation of that. I bet it's an implementation issue with whatever Arny is using, probably due to rounding. Alternatively, if your equipment will handle it, try creating the wave models at 24 or 32/96, or even 32/192, you'll see a considerable difference in your results, especially at higher HF tones and FFT numbers, and your results will be more consistent across the entire range of LF and HF tones. I'd also like to see a believable further explanation of that. This definitely sounds like a numeric precision issue. --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis." |
#344
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Of course it will. And its instanteious velocity is added to the
instantaneous velocity due to the upper note. Okay, but it seems like people are saying that this isn't the case, and is the reason doppler distortion would NOT occur, which seems plain bizzare, IMHO. Surely, as the lower frequency moves the cone back and forth, which at the same time is vibrating to create the higher frequency, that is IDENTICAL to moving a single vibrating source back and forth, like the train analogy (except the train doesn't move back and forth unless the driver is very confused). Therefore, the doppler effect surely DOES occur. It just seems really obvious, so I must be missing the whole point of this, I'm no physics scientist ! -- Mark Simonetti. Freelance Software Engineer. |
#345
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One of the problems with FFT analysis that we've all overlooked is
that we aren't really dealing with analog waveforms in our simulations, and we can get erroneous results when using high FFT numbers because we start playing in the digital "cracks", so to speak, I have to agree with Arny on this. (I used to do FFT and waterfall measurements when I reviewed for Stereophile.) Higher sampling rates are almost always better, other than their effect on measuring LF response. Regardless, the higher the rate, the _fewer_ the cracks. |
#346
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"Mark Simonetti" Surely, as the lower frequency moves the cone back and forth, which at the same time is vibrating to create the higher frequency, that is IDENTICAL to moving a single vibrating source back and forth, like the train analogy (except the train doesn't move back and forth unless the driver is very confused). Therefore, the doppler effect surely DOES occur. It just seems really obvious, so I must be missing the whole point of this, I'm no physics scientist ! ** The matter is intuitive to many - but forever obscure to those with no mental capacity to imagine the situation in their heads. It pretty much divides up between the science types ( using mental, physical models ) and the arts subject types ( using only grammar and phrase matching). The fact that cones have **vastly greater** excursions at low frequencies than at high ones - even for the same SPL - is at the heart of the matter and clearly bamboozles as well. The fact that those large low frequency excursions have the greatest velocity also confounds the easily confoundable. .............. Phil |
#347
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"Mark Simonetti" wrote in message
Of course it will. And its instanteious velocity is added to the instantaneous velocity due to the upper note. Okay, but it seems like people are saying that this isn't the case, and is the reason doppler distortion would NOT occur, which seems plain bizzare, IMHO. So bizarre, that it is in fact fallacious. Surely, as the lower frequency moves the cone back and forth, which at the same time is vibrating to create the higher frequency, that is IDENTICAL to moving a single vibrating source back and forth, like the train analogy (except the train doesn't move back and forth unless the driver is very confused). Agreed. Therefore, the doppler effect surely DOES occur. Agreed. It just seems really obvious, so I must be missing the whole point of this, I'm no physics scientist ! I've got two years of physics, an undergraduate degree in engineering and completed most of my MSE except for my thesis project (wife's pregnancy ended that). I've also measured it quite conclusively in the lab. I've been reading papers about it for like 30 years in the JAES and JASA. Yes, I think that Doppler distortion exist in speakers, but no I don't think it is a serious issue. In contrast the AM distortion in speakers is a very serious, audible issue. |
#348
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Arny Krueger wrote:
I've got two years of physics, an undergraduate degree in engineering and completed most of my MSE except for my thesis project (wife's pregnancy ended that). I've also measured it quite conclusively in the lab. I've been reading papers about it for like 30 years in the JAES and JASA. Yes, I think that Doppler distortion exist in speakers, but no I don't think it is a serious issue. In contrast the AM distortion in speakers is a very serious, audible issue. This is a reasonable assessment of the situation. The thing about doppler modulation, though, is that it's really interesting and the math is a lot of fun. Not like typical AM distortion from amplitude nonlinearities, which is dull, even if it's a more significant problem. So I think folks should continue investigating doppler distortion because it's an interesting problem even if not a terribly important one. --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis." |
#349
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Phil Allison wrote:
no mental capacity to imagine the situation in their heads. It pretty much divides up between the science types ( using mental, physical models ) and the arts subject types ( using only grammar and phrase matching). I often find this. When designing and writing software for instance at work, I can see it all in my head, the mechanisms, how things interact and such like. As soon as I try and explain it verbally to someone, I find it difficult to transfer to language. I'm okay if I have time to produce a document though, because then I have time to translate the visualisation into words, and I can use diagrams. In my original post about this, I had the same problem, I wanted to draw diagrams showing the waves being summed, and the speaker in its different position, etc. -- Mark Simonetti. Freelance Software Engineer. |
#350
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"Mark Simonetti" no mental capacity to imagine the situation in their heads. It pretty much divides up between the science types ( using mental, physical models ) and the arts subject types ( using only grammar and phrase matching). I often find this. When designing and writing software for instance at work, I can see it all in my head, the mechanisms, how things interact and such like. As soon as I try and explain it verbally to someone, I find it difficult to transfer to language. I'm okay if I have time to produce a document though, because then I have time to translate the visualisation into words, and I can use diagrams. In my original post about this, I had the same problem, I wanted to draw diagrams showing the waves being summed, and the speaker in its different position, etc. ** The lack of the facility to post sketches and diagrams on usenet is a *real* drawback. When I need to explain stuff to non-technical folk ( and some technical ones too) I often reach for my pen and paper !!!! Then, on second thoughts, the sketches that might appear most often could be kinda pornographic in nature ;-) ........... Phil |
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Phil Allison wrote:
Then, on second thoughts, the sketches that might appear most often could be kinda pornographic in nature ;-) That might not be a bad thing, I mean if it helps get the point across, right? All in the aid of science and all that ;-) -- Mark Simonetti. Freelance Software Engineer. |
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"William Sommerwerck" wrote in message
One of the problems with FFT analysis that we've all overlooked is that we aren't really dealing with analog waveforms in our simulations, and we can get erroneous results when using high FFT numbers because we start playing in the digital "cracks", so to speak, I have to agree with Arny on this. (I used to do FFT and waterfall measurements when I reviewed for Stereophile.) Higher sampling rates are almost always better, other than their effect on measuring LF response. Regardless, the higher the rate, the _fewer_ the cracks. Strictly speaking there are no cracks, its just that the bricks are wider. |
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"Scott Dorsey" wrote in message
Arny Krueger wrote: I've got two years of physics, an undergraduate degree in engineering and completed most of my MSE except for my thesis project (wife's pregnancy ended that). I've also measured it quite conclusively in the lab. I've been reading papers about it for like 30 years in the JAES and JASA. Yes, I think that Doppler distortion exist in speakers, but no I don't think it is a serious issue. In contrast the AM distortion in speakers is a very serious, audible issue. This is a reasonable assessment of the situation. The thing about doppler modulation, though, is that it's really interesting and the math is a lot of fun. Not like typical AM distortion from amplitude nonlinearities, which is dull, even if it's a more significant problem. So I think folks should continue investigating doppler distortion because it's an interesting problem even if not a terribly important one. Thanks, Scott. The other thing about Doppler is that it is in some sense irreducable, and even something that modern speaker development trends seem to want to increase. Some of my informants argue that in fact speakers are about as linear as they ever will be, and that the only remaining approach is to make them cheaper, smaller, and put their nonlinearities where they won't sound so objectionable. This whole discussion traces back to another discussion on another audio groups about a month ago. My opponent in that discussion seems to have considerably changed his position in the past month in a good way, but he still abuses my name. So goes life! |
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Arny Krueger wrote:
Some of my informants argue that in fact speakers are about as linear as they ever will be, and that the only remaining approach is to make them cheaper, smaller, and put their nonlinearities where they won't sound so objectionable. If speakers are as linear as they ever will be, I'm giving up this whole industry and going out to listen only to live music. If this is as good as it gets, it's a total waste. --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis." |
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"Scott Dorsey" wrote in message
Arny Krueger wrote: Some of my informants argue that in fact speakers are about as linear as they ever will be, and that the only remaining approach is to make them cheaper, smaller, and put their nonlinearities where they won't sound so objectionable. If speakers are as linear as they ever will be, I'm giving up this whole industry and going out to listen only to live music. If this I'm almost with you, Scott. |
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"Porky" writes:
"Arny Krueger" wrote in message ... "Porky" wrote in message 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? right. However, its a lot harder to properly measure doppler when the LF tone has a very low frequency. To measure it with a FFT you must use a FFT size that covers at least one cycle, and hopefully several cycles of the process. If the LF tone is 0.1 Hz, this means an absolute minimum of 10 seconds of data, and ideally 30 or more. At 44,100 Hz sampling, this would be a FFT composed of a minimum of 441,000 samples, and preferably several million samples. Consider the original example - the LF tone was 50 Hz. It had an 882 sample period. Note how much overkill there was when analyzed using a 65k sample FFT, or as I used a one million point FFT. One of the problems with FFT analysis that we've all overlooked is that we aren't really dealing with analog waveforms in our simulations, and we can get erroneous results when using high FFT numbers because we start playing in the digital "cracks", so to speak, The waveform being analog or digital makes no difference as long as sufficient bandwidth and dynamic range has been supplied by the A/D conversion. Rather, the problem you are ignorantly referring to is that an FFT implicitly assumes the input is periodic. If it isn't, you can get yourself befuddled. There is also the problem with using the FFT to estimate the spectrum of a random signal - it can be shown that there will be variance in the frequency estimates no matter how many points are used in the FFT (see, for example, "Signal Processing: Discrete Spectral Analysis, Detection, and Estimation," Mischa Schwartz and Leonard Shaw). -- Randy Yates Sony Ericsson Mobile Communications Research Triangle Park, NC, USA , 919-472-1124 |
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Bob,
You seem to think the Doppler effect doesn't happen in speakers beacue the air is moving with the speaker cone. I think this is wrong. The Doppler effect happens anyway. The Doppler effect depends only on the distnace between the Rx and Tx changing. Doppler happens for radio and light waves as well and there is no ether to move or not move. The Doppler effect is a function of the changing distance between the Rx and Tx and has nothing to do with the propogating medium. Mark |
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If speakers are as linear as they ever will be, I'm giving up this whole
industry and going out to listen only to live music. If this is as good as it gets, it's a total waste. If you're talking about simple harmonic and IM distortion, I'm inclined to agree there isn't much room for improvement. But there is great room for improvement in other areas. |
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Porky wrote: One of the problems with FFT analysis that we've all overlooked is that we aren't really dealing with analog waveforms in our simulations, and we can get erroneous results when using high FFT numbers because we start playing in the digital "cracks", so to speak, The FFT gives slightly misleading results due to "edge effects" or the windows that must be applied to eliminate them but after windowing, nothing much gets through the cracks. If we are dealing with signals whose Fourier components have an integral number of cycles in the length of the transform and if the signal doesn't contain anything in the band above half the sample rate than it's exact. Bob -- "Things should be described as simply as possible, but no simpler." A. Einstein |
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Mark Simonetti wrote: Of course it will. And its instanteious velocity is added to the instantaneous velocity due to the upper note. Okay, but it seems like people are saying that this isn't the case, and is the reason doppler distortion would NOT occur, which seems plain bizzare, IMHO. In some circumstances it does and in others it doesn't but that isn't the reason, at any rate, for either result. Bob -- "Things should be described as simply as possible, but no simpler." A. Einstein |
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