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"Porky" wrote in message
... Here's my original statement: If Doppler distortion actually exists at the levels postulated (I believe the amount 26% was posted), then the human hearing must have a mechanism to compensate for it because we don't hear it. You're lying again. Your original statement was, "From a practical standpoint, the question isn't whether Doppler shift exists in a loudspeaker, the real issue is whether or not it's audible, and if it is audible, whether or not our hearing has a mechanism to compensate for it." http://tinyurl.com/4b3xg There was no discussion for 26% at the time. In fact in that same post you wrote, "I would suggest that until someone builds a computer model of a real loudspeaker reproducing real music in a real room, comes up with the necessary algorythms and runs the simulation, no accurate, or even approximate solution for the real world issue is going to be found." My personal take on it is that if Doppler distortion does exist it is at inaudible levels. If you have another alternative, you're welcome to post it and argue in its favor, but don't start taking things I say out of context and trying to twist them to mean something I obviously didn't intend. Explain to me how I twisted your actual statement. YOU twisted it. There's no way the brain automatically compensates for it. Many of us explained why. It's not a "real" issue. Instead of agreeing, you started with that either/or crap so as not to take responsibility for what you said. Once again if you'd just admit you were wrong instead of arguing endlessly about what you said, we wouldn't be in this mess. |
#122
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"Jim Carr" wrote in message news:gcL9d.10577$_a3.4635@fed1read05... "Porky" wrote in message . .. "Jim Carr" wrote in message news:jJp9d.3557$_a3.1033@fed1read05... "Porky" wrote in message t... It was Doppler's train experiment, not Einstein's. You've obviously never read "Relativity - The Special and General Theory" by some old guy named Albert Einstein. He only mentions the train and embankment about a zillion times. But since this thread is about Doppler shift in a speaker, Doppler's train experiment is the more relevant one, is it not? The person to whom you were replying talked about the Lorentz Transformation and referred to "relatavistic mumbo-jumbo" so he was certainly entitled to refer to Einstein. Since you were a smart-ass to him, I was a smart-ass back to you. Fair enough, but did you understand anything he said? Specifically, "The brain has nothing to do with light or sound. It's the geometric relationship bewteen eye sockets, ear sockets, and wind that create the sound." or "Most mediums, including the Earth's crust, the Ocean Bottom, clouds, and the sun's photosphere don't have a fixed speed of sound. So the "wavelength" in those media doesn't really exist in the Classical Fourier sense. Which is why you need complex frequencies in those cases. And the imaginary part of the frequency is going to be traveling through a different state of matter than the real part of the frequency. And it's going to travel infinitely faster than the real part. Which is where matrix mechanics and the Uncertainty Prinicple came from. And what the wavelength is in a matrix, nobody knows." Can you tell us what any of that means and, more importantly, what it has to do with recording or home studio? |
#123
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"Jim Carr" wrote in message news:PCL9d.10898$_a3.1977@fed1read05... "Porky" wrote in message ... Wavelength and frequency are directly related and in any medium where the velocity of propagation is constant, as with sound, if one changes, the other has to change as well and the change will be directly proportional, there are no exceptions. Are you being bullheaded or do you really not understand? I've given you mind experiments and mathematics to prove you wrong, and all you can do is repeat your same assertation with no proof. You never admit you're wrong, do you? Show me one post in the hundreds where people have disagreed with you where you admit you're wrong. One thing you're overlooking is that if the receiver is moving, in order to make a valid observation about what he observes, your measuring device has to be moving with him, so the apparent wavelength Here we go again. Go back to the stationary source. The first wave strikes the receiver. The receiver moves towards the source then STOPS BEFORE THE SECOND WAVE ARRIVES. According to you since the receiver is not moving I don't have to worry about the measuring stick moving. At the moment the second wave strikes the receiver I take my measurement between it and the first wave. If the receiver stops, he will hear the sound at it's actual frequency, it is ONLY when there is relative motion between the source and the receiver that a pitch shift is heard, if you stop the motion you stop the shift. What's that distance? If you said the same as at the source, you would be correct. Yes, because the receiver has stopped and there is NO motion between the source and the receiver, and thus, no Doppler shift! You can't stop to take measurements because that changes the relative motion between sourece and receiver on which Doppler shift is based. What's the frequency? Obviously the frequency is greater than at the source because the second wave traveled for less time/distance before striking the receiver. But the instant the receiver stopped, the frequency shift stopped too and the receiver hears the actual frequency of the source, As I said, the relationship between frequency and the wavelength is fixed, it cannot be changed without changing the propagation speed of the medium. Thus it is proved again. No, it isn't! Will someone please explain it to Jim? He obviously isn't listening to me. To make it even more confusing, if you are traveling at a different velocity and direction relative to the source than is the receiver, you'll observations will be totally different than his. My formula will correctly determine the wavelength even if the source and receiver are moving. Plug in the numbers and try it yourself. Frequency is time dependent. It tells how often some event occurs such as the wave passing by us. Wavelength is not time dependent. It's the distance between identical points between waves. If the speed is constant, there is a mathematical relationship - on that we agree. If we introduce other movement into the picture, we had better account for it. You can't pretend it didn't happen, can we. You have no problems adjusting the frequency based on the movement (Doppler Shift), so you had better adjust the wavelength based on the movement as well. This is my last post on the topic, Porky. If you don't understand by now, you never will. Look, the apparent frequency the listener hears is directly related to the wavelength he sees, in a relationship that is locked together. If C is the speed of sound, W is the wavelength and F the frequency, then the equations for determining wavelength from frequency or frequency from wavelength, W=C/F and F=C/W apply to both sound waves and electromagnetic waves, the only difference being the relative velocities of C for each. If C is a constant, and it is in this case, then the relationship between F and W is absolutely fixed. If you change one by any given percentage, you change the other as well by exactly the same percentage. See: http://cnx.rice.edu/content/m11060/latest/ http://www.installer.com/tech/freqandwave.html - Look at the table, the relationship between frequency and wavelength is fixed, if you change one, you change the other. http://hyperphysics.phy-astr.gsu.edu...ound/dopp.html This one gives graphic representation of the apparent shift in wavelength and thus in frequency as well. http://www.safetyline.wa.gov.au/inst...e53/l53_03.asp http://rockpile.phys.virginia.edu/arc00/arch32.pdf http://www.isvr.soton.ac.uk/SPCG/Tut...-frequency.htm These links cover electromagnetic waves, but if you make C equal the speed of sound, it works for sound too. http://www.1728.com/freqwave.htm http://www.qrg.northwestern.edu/proj...h-related.html http://hubblesite.org/reference_desk...d=72&cat=light http://www.zyra.org.uk/freqwav.htm Jim, you don't seem to understand that the receiver cannot stop to take measurements without the Doppler shift stopping as well. I'll try one last time: It doesn't matter which is moving, as long as there is relative motion there between the source and the receiver there will be Doppler shift in the apparent frequency picked up by the receiver BECAUSE the motion results in the wavelength's apparent shortening or lengthening (depending on direction of the relative motion) as seen by the receiver. If the motion stops, the Doppler shift will stop too, and the receiver will pick up the actual frequency of the source. If I'm being stubborn and bullheaded, it's because I'm trying to help you, because this time I'm right! |
#124
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Porky wrote: "Jim Carr" wrote in message news:PCL9d.10898$_a3.1977@fed1read05... "Porky" wrote in message et... Wavelength and frequency are directly related and in any medium where the velocity of propagation is constant, as with sound, if one changes, the other has to change as well and the change will be directly proportional, there are no exceptions. Are you being bullheaded or do you really not understand? I've given you mind experiments and mathematics to prove you wrong, and all you can do is repeat your same assertation with no proof. You never admit you're wrong, do you? Show me one post in the hundreds where people have disagreed with you where you admit you're wrong. One thing you're overlooking is that if the receiver is moving, in order to make a valid observation about what he observes, your measuring device has to be moving with him, so the apparent wavelength Here we go again. Go back to the stationary source. The first wave strikes the receiver. The receiver moves towards the source then STOPS BEFORE THE SECOND WAVE ARRIVES. According to you since the receiver is not moving I don't have to worry about the measuring stick moving. At the moment the second wave strikes the receiver I take my measurement between it and the first wave. If the receiver stops, he will hear the sound at it's actual frequency, it is ONLY when there is relative motion between the source and the receiver that a pitch shift is heard, if you stop the motion you stop the shift. What's that distance? If you said the same as at the source, you would be correct. Yes, because the receiver has stopped and there is NO motion between the source and the receiver, and thus, no Doppler shift! You can't stop to take measurements because that changes the relative motion between sourece and receiver on which Doppler shift is based. What's the frequency? Obviously the frequency is greater than at the source because the second wave traveled for less time/distance before striking the receiver. But the instant the receiver stopped, the frequency shift stopped too and the receiver hears the actual frequency of the source, As I said, the relationship between frequency and the wavelength is fixed, it cannot be changed without changing the propagation speed of the medium. Thus it is proved again. No, it isn't! Will someone please explain it to Jim? He obviously isn't listening to me. To make it even more confusing, if you are traveling at a different velocity and direction relative to the source than is the receiver, you'll observations will be totally different than his. My formula will correctly determine the wavelength even if the source and receiver are moving. Plug in the numbers and try it yourself. Frequency is time dependent. It tells how often some event occurs such as the wave passing by us. Wavelength is not time dependent. It's the distance between identical points between waves. If the speed is constant, there is a mathematical relationship - on that we agree. If we introduce other movement into the picture, we had better account for it. You can't pretend it didn't happen, can we. You have no problems adjusting the frequency based on the movement (Doppler Shift), so you had better adjust the wavelength based on the movement as well. This is my last post on the topic, Porky. If you don't understand by now, you never will. Look, the apparent frequency the listener hears is directly related to the wavelength he sees, in a relationship that is locked together. If C is the speed of sound, W is the wavelength and F the frequency, then the equations for determining wavelength from frequency or frequency from wavelength, W=C/F and F=C/W apply to both sound waves and electromagnetic waves, the only difference being the relative velocities of C for each. If C is a constant, and it is in this case, then the relationship between F and W is absolutely fixed. If you change one by any given percentage, you change the other as well by exactly the same percentage. See: http://cnx.rice.edu/content/m11060/latest/ http://www.installer.com/tech/freqandwave.html - Look at the table, the relationship between frequency and wavelength is fixed, if you change one, you change the other. http://hyperphysics.phy-astr.gsu.edu...ound/dopp.html This one gives graphic representation of the apparent shift in wavelength and thus in frequency as well. http://www.safetyline.wa.gov.au/inst...e53/l53_03.asp http://rockpile.phys.virginia.edu/arc00/arch32.pdf http://www.isvr.soton.ac.uk/SPCG/Tut...-frequency.htm These links cover electromagnetic waves, but if you make C equal the speed of sound, it works for sound too. http://www.1728.com/freqwave.htm http://www.qrg.northwestern.edu/proj...h-related.html http://hubblesite.org/reference_desk...d=72&cat=light http://www.zyra.org.uk/freqwav.htm Jim, you don't seem to understand that the receiver cannot stop to take measurements without the Doppler shift stopping as well. I'll try one last time: It doesn't matter which is moving, as long as there is relative motion there between the source and the receiver there will be Doppler shift in the apparent frequency picked up by the receiver BECAUSE the motion results in the wavelength's apparent shortening or lengthening (depending on direction of the relative motion) as seen by the receiver. If the motion stops, the Doppler shift will stop too, and the receiver will pick up the actual frequency of the source. If I'm being stubborn and bullheaded, it's because I'm trying to help you, because this time I'm right! Both of you have completely omitted the role of the medium in determining wavelength. The wavelength is given by wavelength = (u - cos v)/freq where u is the velocity of the wave wrt the medium, and v is the velocity of the source wrt the medium. Take the cosine of the angle formed between a specific "ray" and the direction of motion of the source wrt the that ray. freq is the source frequency, i.e. wrt the source frame. Obviously, according to this equation, when the source is in motion wrt the medium, the wavelength varies with direction of wave propagation from the point of origin in the medium. Thus the detected frequency will differ for various observers that are perfectly at rest wrt each other, i.e. when those observers are positioned along the circumference of a circle that surrounds the source. The frequency detected by any detector will be given by freq' = (u - cos' v')/wavelength where freq' is the detected frequency, and v' is the velocity of the detector wrt the medium. Since the wavelength is invariant, then by substitution: freq' = freq(u - cos' v')/ (u - cos v) When the source and observer are moving wrt each other in a head on path, then cos = cos' = 1 and the equation reduces to freq' = freq(u - v')/ (u - v) or freq' = freq(1 - v'/u)/ (1 - v/u) The doppler shift is thus not proportional to the velocity of the source wrt the detector. IOW, the equation wavelength = u/freq is only valid when the frequency is that measured by a detector or by a source that is at rest wrt the medium. Since in the context of special relativity the source and detector are always at rest wrt the medium in their own frames respectively, then the equation wavelength = c/freq is adopted as universally true. IOW, this form is invalid for sound waves, or any type of matter wave, where the terms (cos v) and (cos' v') don't drop out of the doppler equations if and when they are non zero. Because they are zero in the case of light propagation and special relativity, they do in fact drop out, leaving the equation above. Hope this helps. Pick up "Schaum's outlines: Physics for Science and Engineering". The section on doppler theory is very clearly written. I don't know what doppler distortion might be. I think someone has too much time on their hands. Richard Perry |
#125
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"RP" wrote in message ... Porky wrote: "Jim Carr" wrote in message news:PCL9d.10898$_a3.1977@fed1read05... "Porky" wrote in message et... Wavelength and frequency are directly related and in any medium where the velocity of propagation is constant, as with sound, if one changes, the other has to change as well and the change will be directly proportional, there are no exceptions. Are you being bullheaded or do you really not understand? I've given you mind experiments and mathematics to prove you wrong, and all you can do is repeat your same assertation with no proof. You never admit you're wrong, do you? Show me one post in the hundreds where people have disagreed with you where you admit you're wrong. One thing you're overlooking is that if the receiver is moving, in order to make a valid observation about what he observes, your measuring device has to be moving with him, so the apparent wavelength Here we go again. Go back to the stationary source. The first wave strikes the receiver. The receiver moves towards the source then STOPS BEFORE THE SECOND WAVE ARRIVES. According to you since the receiver is not moving I don't have to worry about the measuring stick moving. At the moment the second wave strikes the receiver I take my measurement between it and the first wave. If the receiver stops, he will hear the sound at it's actual frequency, it is ONLY when there is relative motion between the source and the receiver that a pitch shift is heard, if you stop the motion you stop the shift. What's that distance? If you said the same as at the source, you would be correct. Yes, because the receiver has stopped and there is NO motion between the source and the receiver, and thus, no Doppler shift! You can't stop to take measurements because that changes the relative motion between sourece and receiver on which Doppler shift is based. What's the frequency? Obviously the frequency is greater than at the source because the second wave traveled for less time/distance before striking the receiver. But the instant the receiver stopped, the frequency shift stopped too and the receiver hears the actual frequency of the source, As I said, the relationship between frequency and the wavelength is fixed, it cannot be changed without changing the propagation speed of the medium. Thus it is proved again. No, it isn't! Will someone please explain it to Jim? He obviously isn't listening to me. To make it even more confusing, if you are traveling at a different velocity and direction relative to the source than is the receiver, you'll observations will be totally different than his. My formula will correctly determine the wavelength even if the source and receiver are moving. Plug in the numbers and try it yourself. Frequency is time dependent. It tells how often some event occurs such as the wave passing by us. Wavelength is not time dependent. It's the distance between identical points between waves. If the speed is constant, there is a mathematical relationship - on that we agree. If we introduce other movement into the picture, we had better account for it. You can't pretend it didn't happen, can we. You have no problems adjusting the frequency based on the movement (Doppler Shift), so you had better adjust the wavelength based on the movement as well. This is my last post on the topic, Porky. If you don't understand by now, you never will. Look, the apparent frequency the listener hears is directly related to the wavelength he sees, in a relationship that is locked together. If C is the speed of sound, W is the wavelength and F the frequency, then the equations for determining wavelength from frequency or frequency from wavelength, W=C/F and F=C/W apply to both sound waves and electromagnetic waves, the only difference being the relative velocities of C for each. If C is a constant, and it is in this case, then the relationship between F and W is absolutely fixed. If you change one by any given percentage, you change the other as well by exactly the same percentage. See: http://cnx.rice.edu/content/m11060/latest/ http://www.installer.com/tech/freqandwave.html - Look at the table, the relationship between frequency and wavelength is fixed, if you change one, you change the other. http://hyperphysics.phy-astr.gsu.edu...ound/dopp.html This one gives graphic representation of the apparent shift in wavelength and thus in frequency as well. http://www.safetyline.wa.gov.au/inst...e53/l53_03.asp http://rockpile.phys.virginia.edu/arc00/arch32.pdf http://www.isvr.soton.ac.uk/SPCG/Tut...-frequency.htm These links cover electromagnetic waves, but if you make C equal the speed of sound, it works for sound too. http://www.1728.com/freqwave.htm http://www.qrg.northwestern.edu/proj...h-related.html http://hubblesite.org/reference_desk...d=72&cat=light http://www.zyra.org.uk/freqwav.htm Jim, you don't seem to understand that the receiver cannot stop to take measurements without the Doppler shift stopping as well. I'll try one last time: It doesn't matter which is moving, as long as there is relative motion there between the source and the receiver there will be Doppler shift in the apparent frequency picked up by the receiver BECAUSE the motion results in the wavelength's apparent shortening or lengthening (depending on direction of the relative motion) as seen by the receiver. If the motion stops, the Doppler shift will stop too, and the receiver will pick up the actual frequency of the source. If I'm being stubborn and bullheaded, it's because I'm trying to help you, because this time I'm right! Both of you have completely omitted the role of the medium in determining wavelength. The wavelength is given by wavelength = (u - cos v)/freq where u is the velocity of the wave wrt the medium, and v is the velocity of the source wrt the medium. Take the cosine of the angle formed between a specific "ray" and the direction of motion of the source wrt the that ray. freq is the source frequency, i.e. wrt the source frame. Obviously, according to this equation, when the source is in motion wrt the medium, the wavelength varies with direction of wave propagation from the point of origin in the medium. Thus the detected frequency will differ for various observers that are perfectly at rest wrt each other, i.e. when those observers are positioned along the circumference of a circle that surrounds the source. The frequency detected by any detector will be given by freq' = (u - cos' v')/wavelength where freq' is the detected frequency, and v' is the velocity of the detector wrt the medium. I believe I covered that in a general sense under the relative motion and direction of travel of the source and receiver(s), and with this quote from my previous post, " To make it even more confusing, if you are traveling at a different velocity and direction relative to the source than is the receiver, you'll observations will be totally different than his.". Since the wavelength is invariant, then by substitution: freq' = freq(u - cos' v')/ (u - cos v) When the source and observer are moving wrt each other in a head on path, then cos = cos' = 1 and the equation reduces to freq' = freq(u - v')/ (u - v) or freq' = freq(1 - v'/u)/ (1 - v/u) The doppler shift is thus not proportional to the velocity of the source wrt the detector. IOW, the equation wavelength = u/freq is only valid when the frequency is that measured by a detector or by a source that is at rest wrt the medium. True but "apparent wavelength = u/ apparent frequency" is valid when the measrements are done by the receiver. Regardless, the relationship of the receiver's perceived frequency to perceived wavelength is a fixed one, if one changes the other will too. To figure Doppler shift you have to take into account both relative velocity and direction, otherwise you have no idea which way the freuqnecy is shifting. Since in the context of special relativity the source and detector are always at rest wrt the medium in their own frames respectively, then the equation wavelength = c/freq is adopted as universally true. IOW, this form is invalid for sound waves, or any type of matter wave, where the terms (cos v) and (cos' v') don't drop out of the doppler equations if and when they are non zero. Because they are zero in the case of light propagation and special relativity, they do in fact drop out, leaving the equation above. Hope this helps. Pick up "Schaum's outlines: Physics for Science and Engineering". The section on doppler theory is very clearly written. I was trying to keep it simple, but your observations are correct and valid, thanks. :-) I don't know what doppler distortion might be. I think someone has too much time on their hands. That's what we're trying to figure out, and you might be right. :-) |
#126
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Porky wrote: "RP" wrote in message ... Porky wrote: "Jim Carr" wrote in message news:PCL9d.10898$_a3.1977@fed1read05... "Porky" wrote in message .net... Wavelength and frequency are directly related and in any medium where the velocity of propagation is constant, as with sound, if one changes, the other has to change as well and the change will be directly proportional, there are no exceptions. Are you being bullheaded or do you really not understand? I've given you mind experiments and mathematics to prove you wrong, and all you can do is repeat your same assertation with no proof. You never admit you're wrong, do you? Show me one post in the hundreds where people have disagreed with you where you admit you're wrong. One thing you're overlooking is that if the receiver is moving, in order to make a valid observation about what he observes, your measuring device has to be moving with him, so the apparent wavelength Here we go again. Go back to the stationary source. The first wave strikes the receiver. The receiver moves towards the source then STOPS BEFORE THE SECOND WAVE ARRIVES. According to you since the receiver is not moving I don't have to worry about the measuring stick moving. At the moment the second wave strikes the receiver I take my measurement between it and the first wave. If the receiver stops, he will hear the sound at it's actual frequency, it is ONLY when there is relative motion between the source and the receiver that a pitch shift is heard, if you stop the motion you stop the shift. What's that distance? If you said the same as at the source, you would be correct. Yes, because the receiver has stopped and there is NO motion between the source and the receiver, and thus, no Doppler shift! You can't stop to take measurements because that changes the relative motion between sourece and receiver on which Doppler shift is based. What's the frequency? Obviously the frequency is greater than at the source because the second wave traveled for less time/distance before striking the receiver. But the instant the receiver stopped, the frequency shift stopped too and the receiver hears the actual frequency of the source, As I said, the relationship between frequency and the wavelength is fixed, it cannot be changed without changing the propagation speed of the medium. Thus it is proved again. No, it isn't! Will someone please explain it to Jim? He obviously isn't listening to me. To make it even more confusing, if you are traveling at a different velocity and direction relative to the source than is the receiver, you'll observations will be totally different than his. My formula will correctly determine the wavelength even if the source and receiver are moving. Plug in the numbers and try it yourself. Frequency is time dependent. It tells how often some event occurs such as the wave passing by us. Wavelength is not time dependent. It's the distance between identical points between waves. If the speed is constant, there is a mathematical relationship - on that we agree. If we introduce other movement into the picture, we had better account for it. You can't pretend it didn't happen, can we. You have no problems adjusting the frequency based on the movement (Doppler Shift), so you had better adjust the wavelength based on the movement as well. This is my last post on the topic, Porky. If you don't understand by now, you never will. Look, the apparent frequency the listener hears is directly related to the wavelength he sees, in a relationship that is locked together. If C is the speed of sound, W is the wavelength and F the frequency, then the equations for determining wavelength from frequency or frequency from wavelength, W=C/F and F=C/W apply to both sound waves and electromagnetic waves, the only difference being the relative velocities of C for each. If C is a constant, and it is in this case, then the relationship between F and W is absolutely fixed. If you change one by any given percentage, you change the other as well by exactly the same percentage. See: http://cnx.rice.edu/content/m11060/latest/ http://www.installer.com/tech/freqandwave.html - Look at the table, the relationship between frequency and wavelength is fixed, if you change one, you change the other. http://hyperphysics.phy-astr.gsu.edu...ound/dopp.html This one gives graphic representation of the apparent shift in wavelength and thus in frequency as well. http://www.safetyline.wa.gov.au/inst...e53/l53_03.asp http://rockpile.phys.virginia.edu/arc00/arch32.pdf http://www.isvr.soton.ac.uk/SPCG/Tut...-frequency.htm These links cover electromagnetic waves, but if you make C equal the speed of sound, it works for sound too. http://www.1728.com/freqwave.htm http://www.qrg.northwestern.edu/proj...h-related.html http://hubblesite.org/reference_desk...d=72&cat=light http://www.zyra.org.uk/freqwav.htm Jim, you don't seem to understand that the receiver cannot stop to take measurements without the Doppler shift stopping as well. I'll try one last time: It doesn't matter which is moving, as long as there is relative motion there between the source and the receiver there will be Doppler shift in the apparent frequency picked up by the receiver BECAUSE the motion results in the wavelength's apparent shortening or lengthening (depending on direction of the relative motion) as seen by the receiver. If the motion stops, the Doppler shift will stop too, and the receiver will pick up the actual frequency of the source. If I'm being stubborn and bullheaded, it's because I'm trying to help you, because this time I'm right! Both of you have completely omitted the role of the medium in determining wavelength. The wavelength is given by wavelength = (u - cos v)/freq where u is the velocity of the wave wrt the medium, and v is the velocity of the source wrt the medium. Take the cosine of the angle formed between a specific "ray" and the direction of motion of the source wrt the that ray. freq is the source frequency, i.e. wrt the source frame. Obviously, according to this equation, when the source is in motion wrt the medium, the wavelength varies with direction of wave propagation from the point of origin in the medium. Thus the detected frequency will differ for various observers that are perfectly at rest wrt each other, i.e. when those observers are positioned along the circumference of a circle that surrounds the source. The frequency detected by any detector will be given by freq' = (u - cos' v')/wavelength where freq' is the detected frequency, and v' is the velocity of the detector wrt the medium. I believe I covered that in a general sense under the relative motion and direction of travel of the source and receiver(s), and with this quote from my previous post, " To make it even more confusing, if you are traveling at a different velocity and direction relative to the source than is the receiver, you'll observations will be totally different than his.". Since the wavelength is invariant, then by substitution: freq' = freq(u - cos' v')/ (u - cos v) When the source and observer are moving wrt each other in a head on path, then cos = cos' = 1 and the equation reduces to freq' = freq(u - v')/ (u - v) or freq' = freq(1 - v'/u)/ (1 - v/u) The doppler shift is thus not proportional to the velocity of the source wrt the detector. IOW, the equation wavelength = u/freq is only valid when the frequency is that measured by a detector or by a source that is at rest wrt the medium. True but "apparent wavelength = u/ apparent frequency" is valid when the measrements are done by the receiver. Regardless, the relationship of the receiver's perceived frequency to perceived wavelength is a fixed one, if one changes the other will too. To figure Doppler shift you have to take into account both relative velocity and direction, otherwise you have no idea which way the freuqnecy is shifting. Of course direction cannot be discounted, which is why the equations that I posted refer to the velocities rather than to the scalar speeds. In hindsight, my last statement above should have read: wavelength = u/freq is only valid when the frequency is that measured by a detector or source that is at rest wrt the medium, or that is in motion at 90 or 270 deg wrt the projected ray (in which case cos_theta = 0). Or IOW, when (cos v) = 0. But I have no idea what "apparent" wavelength and frequency is supposed to mean, except maybe that the observer was "apparently" wrong about one or the other BTW, for those reading this in the sci.physics NG, note that in the following argument we had to assume a medium in order to derive the special relativistic wavelength-frequency relationship. OTOH the mere existence of a "wavelength" of em radiation should offer a clue Richard Perry Since in the context of special relativity the source and detector are always at rest wrt the medium in their own frames respectively, then the equation wavelength = c/freq is adopted as universally true. IOW, this form is invalid for sound waves, or any type of matter wave, where the terms (cos v) and (cos' v') don't drop out of the doppler equations if and when they are non zero. Because they are zero in the case of light propagation and special relativity, they do in fact drop out, leaving the equation above. Hope this helps. Pick up "Schaum's outlines: Physics for Science and Engineering". The section on doppler theory is very clearly written. I was trying to keep it simple, but your observations are correct and valid, thanks. :-) I don't know what doppler distortion might be. I think someone has too much time on their hands. That's what we're trying to figure out, and you might be right. :-) |
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"RP" wrote in message
... Of course direction cannot be discounted, which is why the equations that I posted refer to the velocities rather than to the scalar speeds. In hindsight, my last statement above should have read: wavelength = u/freq is only valid when the frequency is that measured by a detector or source that is at rest wrt the medium, or that is in motion at 90 or 270 deg wrt the projected ray (in which case cos_theta = 0). Or IOW, when (cos v) = 0. Which agrees with what I was saying, though I admit to never seeing your formulas with cos before. Like I said, this is not my field. If it's okay I'm gonna assume the medium doesn't move for the purposes of this discussion. But I have no idea what "apparent" wavelength and frequency is supposed to mean, except maybe that the observer was "apparently" wrong about one or the other Which, again, agrees with my point. I'll attempt to address "apparent wavelength" if you'll bear with me to the end before responding. You and I are not in disgreement. I'm ignoring Porky. We take the simple wavelength = u/freq formula with everything at rest and we see an inverse relationship between frequency and wavelength. I never disputed that. It's not unique to waves. If automobiles driving at 10 feet per second pass us at a rate of two per second, we can calculate the distance between the cars. It's just grade school algebra that even I can do. Of course, we'll have to measure the same point on each car such as the front bumper (gotta be precise with you physics guys). So, as we discussed Doppler shift, I got to thinking about what was really happening. If my source is moving, then the physical distance between two waves is the speed of the waves times the time interval between waves plus or minus the speed of the source times the time interval. With a stationary receiver and medium we can mathematically derive the frequency at which the receiver encounters the waves. Again, I believe we agree on this part. But as I was thinking about the receiver moving with a stationary medium and source, it occured to me that while his movement alters the frequency at which the waves arrive over time, the distance between the waves really didn't change. Please keep reading as I address this. Therefore, our formula didn't apply anymore. This agrees with your assertation that the formula only works for everything being still. All I did was add to the formula some compensation for the movement of the receiver. With that new formula I ended up calculating the same physical distance for the wavelength at the stationary source regardless of whether the receiver was moving or not. I also used Doppler to get the correct frequency as measured at either source. It's easy to visualize. Drop pebbles into a still pond at a constant rate. We watch the rings radiate from the center. From above we can watch them stay the same distance apart. We see a bee fly over the pond on a bee-line for the point where the pebbles are dropped. How do we calculate the frequency at which the bee passes over each wave? If we know the speed of the waves, the speed of the bee and the frequency of the waves, we can calculate that frequency. This is the Doppler shift formula simply stated. But if we use the simple wavelength formula, we arrive at a number that disagrees with what we see from above. If we use mine, we get the same number. If we use the simple formula (which assumes everything to be still) in this situation with the receiver moving, it REALLY tells us the how far Wave B traveled after the bee crossed over Wave A. Is that wavelength? No. We we know wavelength is defined as the distance between the same points on two waves, NOT the distance traveled. A subtle but important difference. Only in the case of everything being still are the wavelength and the distance traveled the same. For most discussions of audio that assumption suffices. Thus if we use my formula we can arrive at the correct wavelength in all cases of the source or receiver moving in a stationary medium. Am I totally whacked or is my theory, pardon the pun, sound? Just to comment on the semantics: Apparent can mean either readily seen *or* readily clear/understood *or* appearing but not necesarily so. If you say the apparent wavelength changes using the third definition, then we can ignore the movement of the receiver when calculating that number. But why would we do that when we know that formula is only measuring the distance the second wave traveled, not the distance between the same points on the wave? As we've seen we can easily calcuate the correct wavelength. |
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Jim Carr wrote: "RP" wrote in message ... Of course direction cannot be discounted, which is why the equations that I posted refer to the velocities rather than to the scalar speeds. In hindsight, my last statement above should have read: wavelength = u/freq is only valid when the frequency is that measured by a detector or source that is at rest wrt the medium, or that is in motion at 90 or 270 deg wrt the projected ray (in which case cos_theta = 0). Or IOW, when (cos v) = 0. Which agrees with what I was saying, though I admit to never seeing your formulas with cos before. Like I said, this is not my field. If it's okay I'm gonna assume the medium doesn't move for the purposes of this discussion. But I have no idea what "apparent" wavelength and frequency is supposed to mean, except maybe that the observer was "apparently" wrong about one or the other Which, again, agrees with my point. I'll attempt to address "apparent wavelength" if you'll bear with me to the end before responding. You and I are not in disgreement. I'm ignoring Porky. We take the simple wavelength = u/freq formula with everything at rest and we see an inverse relationship between frequency and wavelength. I never disputed that. It's not unique to waves. If automobiles driving at 10 feet per second pass us at a rate of two per second, we can calculate the distance between the cars. It's just grade school algebra that even I can do. Of course, we'll have to measure the same point on each car such as the front bumper (gotta be precise with you physics guys). So, as we discussed Doppler shift, I got to thinking about what was really happening. If my source is moving, then the physical distance between two waves is the speed of the waves times the time interval between waves plus or minus the speed of the source times the time interval. With a stationary receiver and medium we can mathematically derive the frequency at which the receiver encounters the waves. Again, I believe we agree on this part. But as I was thinking about the receiver moving with a stationary medium and source, it occured to me that while his movement alters the frequency at which the waves arrive over time, the distance between the waves really didn't change. Please keep reading as I address this. Therefore, our formula didn't apply anymore. This agrees with your assertation that the formula only works for everything being still. All I did was add to the formula some compensation for the movement of the receiver. With that new formula I ended up calculating the same physical distance for the wavelength at the stationary source regardless of whether the receiver was moving or not. I also used Doppler to get the correct frequency as measured at either source. It's easy to visualize. Drop pebbles into a still pond at a constant rate. We watch the rings radiate from the center. From above we can watch them stay the same distance apart. We see a bee fly over the pond on a bee-line for the point where the pebbles are dropped. How do we calculate the frequency at which the bee passes over each wave? If we know the speed of the waves, the speed of the bee and the frequency of the waves, we can calculate that frequency. This is the Doppler shift formula simply stated. But if we use the simple wavelength formula, we arrive at a number that disagrees with what we see from above. If we use mine, we get the same number. If we use the simple formula (which assumes everything to be still) in this situation with the receiver moving, it REALLY tells us the how far Wave B traveled after the bee crossed over Wave A. Is that wavelength? No. We we know wavelength is defined as the distance between the same points on two waves, NOT the distance traveled. A subtle but important difference. Only in the case of everything being still are the wavelength and the distance traveled the same. For most discussions of audio that assumption suffices. Thus if we use my formula we can arrive at the correct wavelength in all cases of the source or receiver moving in a stationary medium. Am I totally whacked or is my theory, pardon the pun, sound? Just to comment on the semantics: Apparent can mean either readily seen *or* readily clear/understood *or* appearing but not necesarily so. If you say the apparent wavelength changes using the third definition, then we can ignore the movement of the receiver when calculating that number. But why would we do that when we know that formula is only measuring the distance the second wave traveled, not the distance between the same points on the wave? As we've seen we can easily calcuate the correct wavelength. I see that you provided: " W=(C+R)/F where R is the speed of the Receiver" This equation is ok as long as you know what the special case is that you are applying it to. Since you didn't define the system, the equation may or may not get the correct answer when applied by others. Richard Perry |
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"RP" wrote in message ... Of course direction cannot be discounted, which is why the equations that I posted refer to the velocities rather than to the scalar speeds. In hindsight, my last statement above should have read: wavelength = u/freq is only valid when the frequency is that measured by a detector or source that is at rest wrt the medium, or that is in motion at 90 or 270 deg wrt the projected ray (in which case cos_theta = 0). Or IOW, when (cos v) = 0. But I have no idea what "apparent" wavelength and frequency is supposed to mean, except maybe that the observer was "apparently" wrong about one or the other The "apparent" wavelength and frequency are what the receiver observes, as opposed to the actual frequency and wavelength as it appears at the source. "Apparent" in this case meaning "as it appears" to the receiver. If there is relative motion between the source and receiver, the apparent wavelength observed by the reseiver will be different from the actual wavelength and frequency produced by the source, this difference is Doppler shift. Therefore, you have the actual frequency and wavelength emitted by the source and the apparent frequency and wavelength as it is observed by the receiver. We are worried only about Doppler shift in sound as it applies to recording and home studio. BTW, for those reading this in the sci.physics NG, note that in the following argument we had to assume a medium in order to derive the special relativistic wavelength-frequency relationship. OTOH the mere existence of a "wavelength" of em radiation should offer a clue I don't think we're really worried about relativistic aspects, and since we live in the earth's atmosphere and of necessity use air as our primary medium of acoustic propogation when listening to music, there is no reason to assume a medium, we are not concerned with EM radiation, just sound in air. For that reason, I'm taking sci.physics off the cross posting list, just to keep it simple and on topic. |
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"Jim Carr" wrote in message news:HHZ9d.14497$_a3.4819@fed1read05... "RP" wrote in message ... Of course direction cannot be discounted, which is why the equations that I posted refer to the velocities rather than to the scalar speeds. In hindsight, my last statement above should have read: wavelength = u/freq is only valid when the frequency is that measured by a detector or source that is at rest wrt the medium, or that is in motion at 90 or 270 deg wrt the projected ray (in which case cos_theta = 0). Or IOW, when (cos v) = 0. Which agrees with what I was saying, though I admit to never seeing your formulas with cos before. Like I said, this is not my field. If it's okay I'm gonna assume the medium doesn't move for the purposes of this discussion. But I have no idea what "apparent" wavelength and frequency is supposed to mean, except maybe that the observer was "apparently" wrong about one or the other Which, again, agrees with my point. I'll attempt to address "apparent wavelength" if you'll bear with me to the end before responding. You and I are not in disgreement. I'm ignoring Porky. We take the simple wavelength = u/freq formula with everything at rest and we see an inverse relationship between frequency and wavelength. I never disputed that. It's not unique to waves. If automobiles driving at 10 feet per second pass us at a rate of two per second, we can calculate the distance between the cars. It's just grade school algebra that even I can do. Of course, we'll have to measure the same point on each car such as the front bumper (gotta be precise with you physics guys). So, as we discussed Doppler shift, I got to thinking about what was really happening. If my source is moving, then the physical distance between two waves is the speed of the waves times the time interval between waves plus or minus the speed of the source times the time interval. With a stationary receiver and medium we can mathematically derive the frequency at which the receiver encounters the waves. Again, I believe we agree on this part. But as I was thinking about the receiver moving with a stationary medium and source, it occured to me that while his movement alters the frequency at which the waves arrive over time, the distance between the waves really didn't change. Please keep reading as I address this. Therefore, our formula didn't apply anymore. This agrees with your assertation that the formula only works for everything being still. All I did was add to the formula some compensation for the movement of the receiver. With that new formula I ended up calculating the same physical distance for the wavelength at the stationary source regardless of whether the receiver was moving or not. I also used Doppler to get the correct frequency as measured at either source. It's easy to visualize. Drop pebbles into a still pond at a constant rate. We watch the rings radiate from the center. From above we can watch them stay the same distance apart. We see a bee fly over the pond on a bee-line for the point where the pebbles are dropped. How do we calculate the frequency at which the bee passes over each wave? If we know the speed of the waves, the speed of the bee and the frequency of the waves, we can calculate that frequency. This is the Doppler shift formula simply stated. But if we use the simple wavelength formula, we arrive at a number that disagrees with what we see from above. If we use mine, we get the same number. If we use the simple formula (which assumes everything to be still) in this situation with the receiver moving, it REALLY tells us the how far Wave B traveled after the bee crossed over Wave A. Is that wavelength? No. We we know wavelength is defined as the distance between the same points on two waves, NOT the distance traveled. A subtle but important difference. Only in the case of everything being still are the wavelength and the distance traveled the same. For most discussions of audio that assumption suffices. Thus if we use my formula we can arrive at the correct wavelength in all cases of the source or receiver moving in a stationary medium. Am I totally whacked or is my theory, pardon the pun, sound? Just to comment on the semantics: Apparent can mean either readily seen *or* readily clear/understood *or* appearing but not necesarily so. If you say the apparent wavelength changes using the third definition, then we can ignore the movement of the receiver when calculating that number. But why would we do that when we know that formula is only measuring the distance the second wave traveled, not the distance between the same points on the wave? As we've seen we can easily calcuate the correct wavelength. My whole point was that the frequency and wavelength of a sound have a fixed relationship and if one change, the other must change as well. All other things being equal, you simply cannot have a sound in air that changes in frequency without changing in wavelength, period! If you think otherwise, you think wrong! |
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Porky wrote: My whole point was that the frequency and wavelength of a sound have a fixed relationship and if one change, the other must change as well. All other things being equal, you simply cannot have a sound in air that changes in frequency without changing in wavelength, period! If you think otherwise, you think wrong! As Richard points out, these statements must be carefully qualified. The relationship depends on the speed of sound. The speed of sound in your frame of reference depends on its velocity with respect to the medium and the direction you chose to measure it in with respect to your frame's velocity. That's what Michaelson and Morely were trying to measure to see how fast and in what direction we were moving with respect to the ether. That it never varies with direction is a property of light, not sound because sound actually has a medium whereas light doesn't, as Einstein figured out. If you measure W from within one frame of reference you'd better be using the C that applies to the direction of measurement in that frame of reference to calculate F in that same frame of reference. When you start mixing frames of reference and not considering angles of measurement as y'all have been doing in this sub-thread it gets very confusing, as you've seen. Bob -- "Things should be described as simply as possible, but no simpler." A. Einstein |
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"Bob Cain" wrote in message ... Porky wrote: My whole point was that the frequency and wavelength of a sound have a fixed relationship and if one change, the other must change as well. All other things being equal, you simply cannot have a sound in air that changes in frequency without changing in wavelength, period! If you think otherwise, you think wrong! As Richard points out, these statements must be carefully qualified. The relationship depends on the speed of sound. The speed of sound in your frame of reference depends on its velocity with respect to the medium and the direction you chose to measure it in with respect to your frame's velocity. That's what Michaelson and Morely were trying to measure to see how fast and in what direction we were moving with respect to the ether. That it never varies with direction is a property of light, not sound because sound actually has a medium whereas light doesn't, as Einstein figured out. If you measure W from within one frame of reference you'd better be using the C that applies to the direction of measurement in that frame of reference to calculate F in that same frame of reference. When you start mixing frames of reference and not considering angles of measurement as y'all have been doing in this sub-thread it gets very confusing, as you've seen. Is it not true that for a specific value of the speed of propagation, C, the relationship of wavelength to frequency is a fixed one, and in order for that relationship of wavelength to frequency to change, C must change as well? The whole point I was trying to make is that if one assumes that the velocity and direction of motion between them is constant, the receiver will see a fixed relationship between the frequency and wavelength of the sound he hears. I'm talking about the typical Doppler shift one is likely to encounter in everyday life, like a train whistle, a siren on an emergency vehicle, or a car engine as it approaches and passes. In other words, Doppler shift as one is likely to encounter it in a recording or home studio enviornment. This assumes that the air will retain roughly the same characteristics during the time one observes a particular instance of Doppler shift. I think most of those interested in the phenomena as it affects the topics of the various recording groups have little interest in anything other than the basics. Jim made statements about observed frequency being shifted while observed wavelength stayed the same, and everything I've ever seen about Doppler shift, as it applies to sound in air, indicated that the apparent shift in frequency the receiver observed is due to the apparent shift in wavelength caused by the relative motion between the source and the receiver. Does the value of C actually change because of the relative motion between the source and the receiver? If so, how does that happen since that motion is relative and not absolute? And if so, how does the absolute velocity of either of or both the source and receiver affect the change in C? |
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"RP" wrote in message
... " W=(C+R)/F where R is the speed of the Receiver" This equation is ok as long as you know what the special case is that you are applying it to. Since you didn't define the system, the equation may or may not get the correct answer when applied by others. The above will work whether the receiver is moving or the source is moving and we use Doppler to calculate F at the source *or* we skip Doppler and simply measure F at the receiver. It does not take into account the medium moving. We're pretty much in agreement that I'm talking about specific scenarios. Doppler was explained to me as a kid. It made perfect sense. I know you fully understand it better than I. Just for kicks I decided to look at a dozen sites all explaining Doppler. In most of them they *only* mentioned the source moving. Some included a formula that handled the receiver moving as well. However, in *every* site I saw that used a picture, they used some form of the concentric circles similar to what I described regarding the pond. One picture was a stationary source with perfectly concentric circles. The distances between the lines we are told is the wavelength. With the source moving in a straight line we see a different picture. You can clearly see that on one side the lines are closer together and on the opposite side they are farther apart than in the first picture. Since the distance between the lines is the wavelength, we can see how the wavelength changes. This link is a great example: http://www.fearofphysics.com/Sound/dopwhy2.html Seeing it this way makes it easy to understand. But nobody showed a picture of the receiver moving. What would the lines look like if the receiver was moving and the source was stationary? The lines would look exactly the same as the first case when the source was stationary. But we're told that the receiver sees a different frequency. It doesn't just "appear" to be a different frequency. Every tool we use to measure the frequency will arrive at the same value. How can the distance between the lines be the same when we acknowledge the frequency at the point of the observer is different than that at the emitter when Porky says the wavelength/frequency relationship is fixed - period? It's simple, and I know you know. After you calculate the wavelength mathematically using Porky's formula, you gotta add/subtract the distance the receiver traveled. If you're moving, Porky's formula tells you how far the wave traveled, not the distance between two equal points on a wave (wavelength). Why he refuses to acknowledge this escapes me. If he wants to argue that there's not much practical use for it, I wouldn't mind. Here's an example using a horn. My limited understanding is that there is a mathematical relationship between the length and flare of the horn and the lowest note it can reproduce properly/well/at all. If I am misstating the above, humor me and pretend I'm right for the sake of argument. If someone is using a horn and says "this is the lowest note it can play properly/well/at all," you could measure the frequency and calculate the length of the horn. If the horn is moving, you're moving (or both) you would still get the right number so long as you know the speed of the movement and apply the Doppler formula. If you didn't account for Doppler, you'd never know the length of the horn. The application of Doppler above implicitly removes the effect of the movement. Intuitively we say we do it because we don't know the right frequency. Once we know the right frequency we can use the fixed relationship between frequency and wavelength to perform our calculations. Another person might argue that there are no wrong frequencies. Either something happens at a certain time interval or it doesn't. There's no ambiguity about how many times per second sound waves strike my microphone. The problem is that when you're moving, you can no longer apply the frequency and speed of the waves to determine the wavelength. You have to account for the movement somehow. In both cases you use Doppler to convert the frequency back to that of a stationary source, then do the calculation. Or, if you're oddball like me, you simply modify your wavelength formula to account for the movement of the source and skip the Doppler formula. Either way the end result is always the same. It's no big deal. |
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Porky wrote: Is it not true that for a specific value of the speed of propagation, C, the relationship of wavelength to frequency is a fixed one, and in order for that relationship of wavelength to frequency to change, C must change as well? Yes, for whatever specific value of C pertains to your frame of reference. Youse guys are using too many words and not enough algebra for me to figure out what you're saying. And if so, how does the absolute velocity of either of or both the source and receiver affect the change in C? Therein lies the crux of both your arguments. What do you think the answer is? Hint: your question is without meaning as stated. You should be asking what is the speed of sound in the frame of reference of the TX, the RX, and the fixed frame of reference of the quiescent air (that's the easy one) and how do you transform the variables among them. Richard spelled that out. Bob -- "Things should be described as simply as possible, but no simpler." A. Einstein |
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Bob Cain wrote: Porky wrote: My whole point was that the frequency and wavelength of a sound have a fixed relationship and if one change, the other must change as well. All other things being equal, you simply cannot have a sound in air that changes in frequency without changing in wavelength, period! If you think otherwise, you think wrong! As Richard points out, these statements must be carefully qualified. The relationship depends on the speed of sound. The speed of sound in your frame of reference depends on its velocity with respect to the medium and the direction you chose to measure it in with respect to your frame's velocity. That's what Michaelson and Morely were trying to measure to see how fast and in what direction we were moving with respect to the ether. That it never varies with direction is a property of light, not sound because sound actually has a medium whereas light doesn't, as Einstein figured out. No, Einstein figured no so thing, only that a particular state of motion couldn't be ascribed to it, i.e. it "seems" to move along with every observer in his own frame. Not so, however, when light speed isn't defined to be constant. The statement that the traveling twin aged less is an admission that his clock ticked slower, i.e. that his standard of measure differed from the stay at home twin's standard. Though both call their unit of time the second, these seconds are not equivalent, thus they should have agreed that the traveling twin call his time unit by some other name. IOW, though both calculated the velocity of some beam of light to be c, it must follow that the velocity actually differed wrt these two, and in fact wrt some third observer the velocity of the first two wrt the beam did in fact differ, since the latter has no difficulty seeing a beam move at 2c wrt another observer, even though that other observer only clocks it at 1c. Thus, if each relies upon a universal standard, i.e. one that remains in equilibrium throughout, then the anisotropy becomes apparent. Richard Perry If you measure W from within one frame of reference you'd better be using the C that applies to the direction of measurement in that frame of reference to calculate F in that same frame of reference. When you start mixing frames of reference and not considering angles of measurement as y'all have been doing in this sub-thread it gets very confusing, as you've seen. Bob |
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RP wrote: That it never varies with direction is a property of light, not sound because sound actually has a medium whereas light doesn't, as Einstein figured out. No, Einstein figured no so thing, only that a particular state of motion couldn't be ascribed to it, i.e. it "seems" to move along with every observer in his own frame. So it was others then that have interpreted his conclusions as making the ether an unnecessary idea? I thought he actually stated that in his paper but it's been quite a while since I read it. Not so, however, when light speed isn't defined to be constant. The statement that the traveling twin aged less is an admission that his clock ticked slower, i.e. that his standard of measure differed from the stay at home twin's standard. Though both call their unit of time the second, these seconds are not equivalent, thus they should have agreed that the traveling twin call his time unit by some other name. IOW, though both calculated the velocity of some beam of light to be c, it must follow that the velocity actually differed wrt these two, and in fact wrt some third observer the velocity of the first two wrt the beam did in fact differ, since the latter has no difficulty seeing a beam move at 2c wrt another observer, even though that other observer only clocks it at 1c. They both see each other's clock's ticking slower but they also see a contraction of distance in the direction of motion of the other. Don't these effects combine to leave the observed c constant for all observers regardless of the frame of reference from which it originated? Bob -- "Things should be described as simply as possible, but no simpler." A. Einstein |
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Bob Cain wrote: RP wrote: That it never varies with direction is a property of light, not sound because sound actually has a medium whereas light doesn't, as Einstein figured out. No, Einstein figured no so thing, only that a particular state of motion couldn't be ascribed to it, i.e. it "seems" to move along with every observer in his own frame. So it was others then that have interpreted his conclusions as making the ether an unnecessary idea? Yes indeed. Einstein saw the necessity of a medium, on logical grounds, though he discounted the common interpretations of it, i.e. as being something that objects have a definite velocity wrt. I thought he actually stated that in his paper but it's been quite a while since I read it. Not so, however, when light speed isn't defined to be constant. The statement that the traveling twin aged less is an admission that his clock ticked slower, i.e. that his standard of measure differed from the stay at home twin's standard. Though both call their unit of time the second, these seconds are not equivalent, thus they should have agreed that the traveling twin call his time unit by some other name. IOW, though both calculated the velocity of some beam of light to be c, it must follow that the velocity actually differed wrt these two, and in fact wrt some third observer the velocity of the first two wrt the beam did in fact differ, since the latter has no difficulty seeing a beam move at 2c wrt another observer, even though that other observer only clocks it at 1c. They both see each other's clock's ticking slower but they also see a contraction of distance in the direction of motion of the other. Don't these effects combine to leave the observed c constant for all observers regardless of the frame of reference from which it originated? Yes indeed again, but keep in mind that these effects occur by sheer fiat, i.e. they are taken as logical premises, and the universe and its interactions are afterward adjusted accordingly to accommodate those presuppositions. The same can be done with virtually any other set of initial premises. OTOH, again, without a universally agreed upon standard, special relativity is automatically disjoint from Newtonian Mechanics without so much as one pen laid to a paper. They are mutually exclusive logical systems, and as such the conclusions of one bear no effect whatsoever on the conclusions of the other. They can both be correct, and moreover one can be correct and the incorrect given exactly the same mathematical conclusion. As B. Russell noted "the resolution to any philosophical argument lies in the definitions of the terms." Richard Perry Bob |
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RP wrote: They are mutually exclusive logical systems, and as such the conclusions of one bear no effect whatsoever on the conclusions of the other. Only because they have a mutually exclusive premise. Newton's theory requires that light veloctities be additive. Einstein's requires the opposite, that it be constant for all observers. From only this difference, the first part of his paper develops his theory purely kinematically and arrives at the Lorentz transformation. They can both be correct, and moreover one can be correct and the incorrect given exactly the same mathematical conclusion. Not sure what you mean here. There is an incorrect premise in Newton's theory that leads to incorrect prediction. Bob -- "Things should be described as simply as possible, but no simpler." A. Einstein |
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Bob Cain wrote: RP wrote: They are mutually exclusive logical systems, and as such the conclusions of one bear no effect whatsoever on the conclusions of the other. Only because they have a mutually exclusive premise. Newton's theory requires that light veloctities be additive. Einstein's requires the opposite, that it be constant for all observers. From only this difference, the first part of his paper develops his theory purely kinematically and arrives at the Lorentz transformation. They can both be correct, and moreover one can be correct and the incorrect given exactly the same mathematical conclusion. Not sure what you mean here. There is an incorrect premise in Newton's theory that leads to incorrect prediction. Which prediction would that be? Richard Perry |
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On Fri, 08 Oct 2004 11:42:55 -0700, Bob Cain
wrote: If the the motion of a test particle normally at rest at a point is purely sinusoidal and containing two tones then First, to expirience doppler effect, we don't need 2 tones. One is enough, but source and listener have to travell (change the distance) relative to each other. Second, molecules of air do not really travell from the speaker towards the listener. If that was the case we'd have wind, not sound. In sound, molecules move in such way, to form areas of higher or lower air pressure (Speaker gives nescesserry energy by means of alternate forward and backward movements). Because of this, pressure wave travell - not matery, length of cones excursion does not influence the freq (or wavelength). Third, the distance btw source and listener is always the same. Fact that cone is sometimes closer, sometimes further changes nothing, because it started "compressing" the air from the neutral position Now, you can say the pressure wave started to travell from he point of max excursion. Yes, but it always does. Therefore the distance does not change. Also, from that same point (moment in time) speaker started "decompressing" the air. All the speaker has to do is to keep pushing and pulling in propper interval so to keep pressure zones equally spaced. Therefore, we can say the distance is constant. If it is constant source dos not travell. If it does not travell there can not possibly be Doppler effect. I think "doppler in speaker" advocates are analyzing the problem, as if there would be two sources, one behind another, appart by the distance of max cone excursion, emmiting sound of same freq. Well, if that was the case, what would be the result heard by listener (being third dot on the same line with two sources)? Can that be called doppler effect? there is a cross phase modulation of each by the other and by itself that appears as IM distortion in the fluid velocity at that same point. It can be called Doppler because standard Doppler shift can be drived from a constant modulation of frequency. Or it can be called Billy. :-) Experiment to prove Doppler effect due to speaker movement, would be to feed the amp with constant tone put a mic infront of a speaker, than measure captured frequency. If ther's fluctuation coinciding with movement, you have doppler. Say we have tone of 100Hz. That's 100 pushes (and 100 pulls). Doppler effect would be present if captured freq would constantly dance arround 100Hz, rise and fall 200 times per second (100 rises and 100 falls) being exactly 100Hz only momentary, while "passing through" neutral position. Obviously, that's not the case. |
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"Porky" wrote in message et...
"Paul Draper" wrote in message om... We're talking at crossed purposes here, and I suppose it depends on what you are measuring when you look at the scope and see a square wave. There are several possibilities: 1. The voltage applied across the terminals of the speaker coil. 2. The current driven through the speaker coil 3. The position of the speaker coil 4. The velocity of the speaker coil 5. The acceleration of the speaker coil 6. The pressure in the air at a point in front of the speaker diaphragm I've been arguing that there is a connection between 4 and 6. Those two, I think, follow the same profile. The others are related through derivatives or integrals, possibly with a phase shift. PD A pure square wave has zero rise and fall times, the "slopes" are vertical. If you apply a square wave to a speaker's terminals, when the positive voltage rise happens, the cone will jump forward and will push the air in front of it. Because of the inertia of the mass of the cone and the air in front of it, the cone will not instantly spring to it's maximum forward position, it will require some period of time, thus the slope of the soundwave being generated will not have a vertical rise time. The same applies to the fall time, again, the slope will not be vertical. Also if the applied square wave is of a low enough frequency, since the average listening room is not air tight, the "top" and "bottom" of the generated soundwave will not be level, they will contain a slope even though the applied electrical square wave has a level "top" and "bottom". As for item (4), in order to follow the square wave's zero rise time, the cone's velocity would have to be infinite, and that can't happen. There is a direct relationship between the velocity of the cone and the rate of change in pressure, so there is a connection between (4) and (6). If one were to apply say, a 20 Hz square wave to a speaker, and record the resulting sound wave, one would see a positive sawtooth wave corresponding to the rise of the wave with a rather abrupt (but not vertical) positive slope and a more gradual negative slope, and then a negative sawtooth wave corresponding to the fall of the wave with a rather abrupt (but not vertical) negative slope and a more gradual positive slope. This is what happens in a real world speaker placed in a real world typical listening room. At higher frequencies, it is possible to reproduce a fair approximation of a square wave, but not a true pure square wave. OK, and now I think I've narrowed down the point of our debate. You think that a voltage applied to the speaker's terminals corresponds to the position of the speaker cone. In the low frequency limit, that may be right. Certainly, if I appy a DC current to the electromagnet, the speaker cone will move to a position where the force applied by the electromagnet balances the elastic restoring force of the cone. But at higher frequencies, I think the situation gets more complicated. First of all, the electromagnet is an inductor, so V = L dI/dt Since the electromagnet is a solenoid, there is something like the relationship B = (mu)nI and so B is proportional to the integral of V with respect to time. And the *force* on the speaker diaphragm is proportional to B, and proportional to the acceleration, not the position of the diaphragm (constant)B = F = ma = m d2(x)/dt2 Thus we have Int(V)dt = (constant) d2(x)/dt2 Thus, the voltage across the terminal is not proportional to the position of the speaker diaphragm, but to the third derivative of the position with respect to time. PD |
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Vladan wrote: First, to expirience doppler effect, we don't need 2 tones. One is enough, but source and listener have to travell (change the distance) relative to each other. Correct, but the effect for a single frequency is very small in comparison to two or more. Second, molecules of air do not really travell from the speaker towards the listener. If that was the case we'd have wind, not sound. In sound, molecules move in such way, to form areas of higher or lower air pressure (Speaker gives nescesserry energy by means of alternate forward and backward movements). They oscillate about a rest position. Because of this, pressure wave travell - not matery, length of cones excursion does not influence the freq (or wavelength). That's what I thought too for a long time. I was wrong. Third, the distance btw source and listener is always the same. Fact that cone is sometimes closer, sometimes further changes nothing, because it started "compressing" the air from the neutral position Now, you can say the pressure wave started to travell from he point of max excursion. Yes, but it always does. Therefore the distance does not change. Also, from that same point (moment in time) speaker started "decompressing" the air. All the speaker has to do is to keep pushing and pulling in propper interval so to keep pressure zones equally spaced. Therefore, we can say the distance is constant. If it is constant source dos not travell. If it does not travell there can not possibly be Doppler effect. Assume that there is an oscilatory motion of particles about a rest position that is imparted linearly by a driver doing the same. Then figure out the fluid velocity at that rest position as a function of the motion of the particles about it. You will find that the relationship predicts intermodulation at that fixed point in an amount related to the size of the excursion of the particles about it. The pressure at that point will be linearly related to the fluid velocity at the point. Thus, a pressure microphone fixed at that rest position will yield signal that contains intermodulation products. If you take that point to be the rest position of the speaker, the potentially large excursions there, on the order of centimeters, can result in a pressure signal propegating from that rest position which contains very signifigant amounts of this IM distortion. The Mackie HR824 has an interesting design that minimizes this. It is only a two way system so should be very prone to low frequencies modulating the mid frequencies. However, the excursion of the Low/Mid driver is small at low frequencies compared to what it would be in a typical ported cabinet. The HR824 cabinet has a tuned passive radiator in the back where the large LF excursion occur separately from the mid range. This effectively makes it a three way system. Tuned ports somewhat accomplish the same thing but not as effecitvely as a passively coupled mass system does. I think "doppler in speaker" advocates are analyzing the problem, as if there would be two sources, one behind another, appart by the distance of max cone excursion, emmiting sound of same freq. Well, if that was the case, what would be the result heard by listener (being third dot on the same line with two sources)? Can that be called doppler effect? An analyis starting from the view of having a high frequency radiator attached and moving with respect to the a low frequency radiator of the same size does correctly depict the situation of the mixed signal being applied to a single radiator. It's just linear superposition. Trying to view this as the velocity of the LF component modulating the frequence of the HF component, as is often done and justified with "dynamic" Doppler shift, is not correct because it does not take into account the fact that the LF component is also generating a wave, not just moving through the air. It predicts an error that is minimum at the ends of the LF excursion where the veolocity due to it is a minimum and a maximum error as the LF motion passes through the rest position where its velocity is a maximum. An analysis that proceeds just from the conditions in a propegating wave, as defined above, predicts the opposite. The latter analysis also applies to the situation where the point in question is the rest position of the speaker due to boundry condition requirements. I don't know what to call the real effect that follows from the correct analysis but it does not follow from thinking of it as "Doppling." Bob -- "Things should be described as simply as possible, but no simpler." A. Einstein |
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RP wrote: Not sure what you mean here. There is an incorrect premise in Newton's theory that leads to incorrect prediction. Which prediction would that be? How about that time and space are a fixed background? Bob -- "Things should be described as simply as possible, but no simpler." A. Einstein |
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"Paul Draper" wrote in message om... "Porky" wrote in message et... "Paul Draper" wrote in message om... We're talking at crossed purposes here, and I suppose it depends on what you are measuring when you look at the scope and see a square wave. There are several possibilities: 1. The voltage applied across the terminals of the speaker coil. 2. The current driven through the speaker coil 3. The position of the speaker coil 4. The velocity of the speaker coil 5. The acceleration of the speaker coil 6. The pressure in the air at a point in front of the speaker diaphragm I've been arguing that there is a connection between 4 and 6. Those two, I think, follow the same profile. The others are related through derivatives or integrals, possibly with a phase shift. PD A pure square wave has zero rise and fall times, the "slopes" are vertical. If you apply a square wave to a speaker's terminals, when the positive voltage rise happens, the cone will jump forward and will push the air in front of it. Because of the inertia of the mass of the cone and the air in front of it, the cone will not instantly spring to it's maximum forward position, it will require some period of time, thus the slope of the soundwave being generated will not have a vertical rise time. The same applies to the fall time, again, the slope will not be vertical. Also if the applied square wave is of a low enough frequency, since the average listening room is not air tight, the "top" and "bottom" of the generated soundwave will not be level, they will contain a slope even though the applied electrical square wave has a level "top" and "bottom". As for item (4), in order to follow the square wave's zero rise time, the cone's velocity would have to be infinite, and that can't happen. There is a direct relationship between the velocity of the cone and the rate of change in pressure, so there is a connection between (4) and (6). If one were to apply say, a 20 Hz square wave to a speaker, and record the resulting sound wave, one would see a positive sawtooth wave corresponding to the rise of the wave with a rather abrupt (but not vertical) positive slope and a more gradual negative slope, and then a negative sawtooth wave corresponding to the fall of the wave with a rather abrupt (but not vertical) negative slope and a more gradual positive slope. This is what happens in a real world speaker placed in a real world typical listening room. At higher frequencies, it is possible to reproduce a fair approximation of a square wave, but not a true pure square wave. OK, and now I think I've narrowed down the point of our debate. You think that a voltage applied to the speaker's terminals corresponds to the position of the speaker cone. Old magnetic meter style voltmeters work on the same principle, but it is the current across a known resistance, not specifically the voltage that makes them work. However, that wasn't what I was trying to get across. With a zero rise time on the squarewave, the voltage rise will be instantaneous from negative value to positive value, However, the cone is not capable of moving instantanoeusly, so there will be some lag in motion both ways. This alone makes the generation of a pure square wave impossible. In the low frequency limit, that may be right. Certainly, if I appy a DC current to the electromagnet, the speaker cone will move to a position where the force applied by the electromagnet balances the elastic restoring force of the cone. But at higher frequencies, I think the situation gets more complicated. You are quite correct, so it will always be impossible to reproduce a pure squarewave with zero rise and fall times, but at higher frequencies the recovery slope of the air in the room will allow fairly (but not perfectly) flat tops and bottoms, so one can get a fair approximation (but only an approximation) of a square wave at higher frequencies. First of all, the electromagnet is an inductor, so V = L dI/dt Since the electromagnet is a solenoid, there is something like the relationship B = (mu)nI and so B is proportional to the integral of V with respect to time. And the *force* on the speaker diaphragm is proportional to B, and proportional to the acceleration, not the position of the diaphragm (constant)B = F = ma = m d2(x)/dt2 Thus we have Int(V)dt = (constant) d2(x)/dt2 Thus, the voltage across the terminal is not proportional to the position of the speaker diaphragm, but to the third derivative of the position with respect to time. I'm not disagreeing with you, I'm just pointing out that a real speaker in a real listening room cannot even approximate a square wave at low frequencies, but can reproduce a fair approximation at higher frequencies. Note that an approximation is not the real thing, and a fair approximation isn't all that accurate an approximation, but it does look fairly close on an oscilloscope. :-) With all due respect to the sci.physics folks, the recording news groups are not particularly concerned with the fine points of theory, we're primarily concerned with good studio techniques and practices. We want practical applications, and rule of thumb is often more practical for us than are complicated exact equations. This is my opinion and others in the recording groups may disagree with me, but for the most part I think many of those in the recording groups simply don't have the physics and math background, they're just trying to get good sounding recordings. They're interested in basic engineering solutions, not complex background theory. I hope no offense is taken, because there certainly is none intended. :-) |
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"Bob Cain" wrote in message ... Vladan wrote: First, to expirience doppler effect, we don't need 2 tones. One is enough, but source and listener have to travell (change the distance) relative to each other. Correct, but the effect for a single frequency is very small in comparison to two or more. Second, molecules of air do not really travell from the speaker towards the listener. If that was the case we'd have wind, not sound. In sound, molecules move in such way, to form areas of higher or lower air pressure (Speaker gives nescesserry energy by means of alternate forward and backward movements). They oscillate about a rest position. Because of this, pressure wave travell - not matery, length of cones excursion does not influence the freq (or wavelength). That's what I thought too for a long time. I was wrong. Third, the distance btw source and listener is always the same. Fact that cone is sometimes closer, sometimes further changes nothing, because it started "compressing" the air from the neutral position Now, you can say the pressure wave started to travell from he point of max excursion. Yes, but it always does. Therefore the distance does not change. Also, from that same point (moment in time) speaker started "decompressing" the air. All the speaker has to do is to keep pushing and pulling in propper interval so to keep pressure zones equally spaced. Therefore, we can say the distance is constant. If it is constant source dos not travell. If it does not travell there can not possibly be Doppler effect. Assume that there is an oscilatory motion of particles about a rest position that is imparted linearly by a driver doing the same. Then figure out the fluid velocity at that rest position as a function of the motion of the particles about it. You will find that the relationship predicts intermodulation at that fixed point in an amount related to the size of the excursion of the particles about it. The pressure at that point will be linearly related to the fluid velocity at the point. Thus, a pressure microphone fixed at that rest position will yield signal that contains intermodulation products. If you take that point to be the rest position of the speaker, the potentially large excursions there, on the order of centimeters, can result in a pressure signal propegating from that rest position which contains very signifigant amounts of this IM distortion. The Mackie HR824 has an interesting design that minimizes this. It is only a two way system so should be very prone to low frequencies modulating the mid frequencies. However, the excursion of the Low/Mid driver is small at low frequencies compared to what it would be in a typical ported cabinet. The HR824 cabinet has a tuned passive radiator in the back where the large LF excursion occur separately from the mid range. This effectively makes it a three way system. Tuned ports somewhat accomplish the same thing but not as effecitvely as a passively coupled mass system does. I think "doppler in speaker" advocates are analyzing the problem, as if there would be two sources, one behind another, appart by the distance of max cone excursion, emmiting sound of same freq. Well, if that was the case, what would be the result heard by listener (being third dot on the same line with two sources)? Can that be called doppler effect? An analyis starting from the view of having a high frequency radiator attached and moving with respect to the a low frequency radiator of the same size does correctly depict the situation of the mixed signal being applied to a single radiator. It's just linear superposition. Trying to view this as the velocity of the LF component modulating the frequence of the HF component, as is often done and justified with "dynamic" Doppler shift, is not correct because it does not take into account the fact that the LF component is also generating a wave, not just moving through the air. It predicts an error that is minimum at the ends of the LF excursion where the veolocity due to it is a minimum and a maximum error as the LF motion passes through the rest position where its velocity is a maximum. An analysis that proceeds just from the conditions in a propegating wave, as defined above, predicts the opposite. The latter analysis also applies to the situation where the point in question is the rest position of the speaker due to boundry condition requirements. I don't know what to call the real effect that follows from the correct analysis but it does not follow from thinking of it as "Doppling." Vladan made the same point that I was trying to make. it isn't Doppler distortion, however Bob is correct that there are IM distortion products, therfore we should try to come up with a different label for the IM distortion Bob is describing, calling it Doppler distortion is just too confusing. |
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Bob Cain wrote: RP wrote: Not sure what you mean here. There is an incorrect premise in Newton's theory that leads to incorrect prediction. Which prediction would that be? How about that time and space are a fixed background? Time, when a universal standard is adopted for use by all observers, whether or not on board clocks perpetually agree with that standard, must necessarily be universal time. Obvious why, eh? Now as for space, acceleration most certainly is absolute, evidenced especially by angular acceleration. I doubt that anyone disputes this. If however, you are referring implicitly to Mach's arguments, then I must concur, i.e. that space is indeed not some static and fixed Euclidean metric in which masses are embedded in. OTOH, whether Newton personally perceived space as such an entity or not, it is immaterial, because his sentiments have no part nor parcel with his math. Thus, show me in a quantitative fashion that Newtonian Mechanics makes an incorrect prediction within its domain of applicability, i.e. the kinematics of neutral masses. If you can do so without utilizing a premise that he did not actually pen, then good luck. Don't try Fizeau's measurements of light speed in moving media, because I've embarrassed enough Ph D's already in that argument by showing them how to correctly compose "average speeds" with the Galilean transform Richard Perry |
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"Jim Greenfield" wrote in message
om... Porky should realise at once that you haven't given him sufficient information (your speed ref the room). As he doesn't understand the implications of mistakenly identifying the _cause_ of Doppler, he might fall for the trap! :-) Jim G c'=c+v Aw, you're no fun!! To recap this entire discussion, it started like this. Porky described Doppler for sound as a shift in the wavelength whether the source or receiver is moving (one should describe it using frequency of the receiver IMHO). I replied that the wavelength certainly does change when the source moves, but it does NOT change when only the receiver moves. He said I was wrong because wavelength and frequency are always in a direct relationship to one another. He cited a few references that did not explicitly discuss the movement of the receiver *and* wavelength specifically. I didn't care because it seemed readily obvious to my uneducated mind. I decided to find a link that discusses wavelength: http://physics.nad.ru/Physics/English/dopp_txt.htm . This site writes, "Next, we shall consider the case when observer moves and the source of the wave is still. In this case the wavelength is NOT changed and Doppler frequency shift appears because the velocity w of the wave relatively the observer is changed." That is certainly a good way of explaining it (which is how you did as well). I never said it that way. My little formula certainly worked that way, but I should have used the phrase "the velocity of the wave relative to the observer is changed." No matter how you slice it if you observe a sound frequency while you're moving, you need to account for that movement when calculating wavelength. You could use Doppler to try to compute the wavelength at the source first and use *that* number, but that requires you know the speed of the source. My method doesn't require it. So as to avoid arguments of relativity I've been talking about sound waves here where the frequency change is different depending on whether the source moves towards the receiver or vice versa. |
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On Mon, 11 Oct 2004 14:40:17 -0700, Bob Cain
wrote: Correct, but the effect for a single frequency is very small in comparison to two or more. I think this is not an argument in the case of wether there is Doppler effect present, or not. I think we agreed there is not. Because of this, pressure wave travell - not matery, length of cones excursion does not influence the freq (or wavelength). That's what I thought too for a long time. I was wrong. I dissagree. I think you have wrong premisse Assume that there is an oscilatory motion of particles about a rest position that is imparted linearly by a driver doing the same.... I think "doppler in speaker" advocates are analyzing the problem, as if there would be two sources, one behind another... An analyis starting from the view of having a high frequency radiator attached and moving with respect to the a low frequency radiator of the same size does correctly depict the situation of the mixed signal being applied to a single radiator. It's just linear superposition.... O.K. I think you say if cone is to produce 2 waves of different freqs at same time, and since excursion it makes to produce one is unrelated to excursion it would make to produce another, that other wave is shifted in a manner similar to doppler effect. I say, speaker does not produce two, or more, pressure waves, for each freq separately, at one time, but rather one result of all the freqs it has to reproduce at that time. Only because ear and mics work analogue to that, we are abele to distinguish two or more tones from that resultant. Also, for producing certain freq, it doesn't matter how far cone goes, but how often. If cone make X full cycles in second, freq is always X, regardles if cone moved 0.1cm, or 1cm. If ther's no shift in freq - ther's no doppler effect. I agree there can be some phase shift, due to various reasons, like inertia, viscosity, displacement....., but none of them produces Doppler effect. |
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Vladan wrote: On Mon, 11 Oct 2004 14:40:17 -0700, Bob Cain wrote: Correct, but the effect for a single frequency is very small in comparison to two or more. I think this is not an argument in the case of wether there is Doppler effect present, or not. I think we agreed there is not. I agree that what's there doesn't follow from a dynamic Doppler analysis where it is the LF velocity shifting the HF frequency. That analysis fails because it assumes the LF motion is not generating any signifigant wave. There is an effect, however, that is very similar in the sense of producing IM distortion that can be very signifigant. Because of this, pressure wave travell - not matery, length of cones excursion does not influence the freq (or wavelength). That's what I thought too for a long time. I was wrong. I dissagree. I think you have wrong premisse An analysis that derives the fluid velocity at a point as a function of the motion of particles normally at rest at that point gives, to a close aproximation, Vf(d,t) = Vd(t - (d + Sd(t - d/c))/c) where Vd(t) and Sd(t) are functions describing the velocity and position of the driver and d is the distance from the driver's rest position to the point. This is a plane wave solution and is a modulation of effective distance between the rest position of the driver and a point a fixed distance away from it. If Vd(t) and Sd(t) are a two frequency mix, the resulting fluid velocity Vf(t) and the proportional pressure at a point a fixed distance from the rest position of the driver will show IM products. O.K. I think you say if cone is to produce 2 waves of different freqs at same time, and since excursion it makes to produce one is unrelated to excursion it would make to produce another, that other wave is shifted in a manner similar to doppler effect. No, I was only trying to say that the compound motion of two drivers receiving separate signals and one driver recieving a compound signal are the same. I say, speaker does not produce two, or more, pressure waves, for each freq separately, at one time, but rather one result of all the freqs it has to reproduce at that time. Only because ear and mics work analogue to that, we are abele to distinguish two or more tones from that resultant. Yes. Also, for producing certain freq, it doesn't matter how far cone goes, but how often. If cone make X full cycles in second, freq is always X, regardles if cone moved 0.1cm, or 1cm. If ther's no shift in freq - ther's no doppler effect. That's what I also thought for too long. The flaw in my view was that the fluid velocity at a point was equal to the velocity of the particles normally at rest there about the point. This produces Vf(d,t) = Vd(t - d/c) instead of the more correct form above and does indicate that there is no distortion at all. This simplifying approximation is made early on in the acoustics texts I've seen without an analyisis the signifigance of that approximation. I don't know if the effect should be called "Doppler" distortion but it's real and in many ways similar. Bob -- "Things should be described as simply as possible, but no simpler." A. Einstein |
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RP wrote: Time, when a universal standard is adopted for use by all observers, whether or not on board clocks perpetually agree with that standard, must necessarily be universal time. Obvious why, eh? Nope. That implies a preferred reference frame and there isn't one. Thus, show me in a quantitative fashion that Newtonian Mechanics makes an incorrect prediction within its domain of applicability, i.e. the kinematics of neutral masses. If you can do so without utilizing a premise that he did not actually pen, then good luck. Don't try Fizeau's measurements of light speed in moving media, because I've embarrassed enough Ph D's already in that argument by showing them how to correctly compose "average speeds" with the Galilean transform I can't. Don't have the Principia at hand. :-) Bob -- "Things should be described as simply as possible, but no simpler." A. Einstein |
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"Jim Carr" wrote in message news:g%Kad.29368$_a3.1912@fed1read05... "Jim Greenfield" wrote in message om... Porky should realise at once that you haven't given him sufficient information (your speed ref the room). As he doesn't understand the implications of mistakenly identifying the _cause_ of Doppler, he might fall for the trap! :-) Jim G c'=c+v Aw, you're no fun!! To recap this entire discussion, it started like this. Porky described Doppler for sound as a shift in the wavelength whether the source or receiver is moving (one should describe it using frequency of the receiver IMHO). I replied that the wavelength certainly does change when the source moves, but it does NOT change when only the receiver moves. He said I was wrong because wavelength and frequency are always in a direct relationship to one another. He cited a few references that did not explicitly discuss the movement of the receiver *and* wavelength specifically. I didn't care because it seemed readily obvious to my uneducated mind. I decided to find a link that discusses wavelength: http://physics.nad.ru/Physics/English/dopp_txt.htm . This site writes, "Next, we shall consider the case when observer moves and the source of the wave is still. In this case the wavelength is NOT changed and Doppler frequency shift appears because the velocity w of the wave relatively the observer is changed." That is certainly a good way of explaining it (which is how you did as well). I never said it that way. My little formula certainly worked that way, but I should have used the phrase "the velocity of the wave relative to the observer is changed." No matter how you slice it if you observe a sound frequency while you're moving, you need to account for that movement when calculating wavelength. You could use Doppler to try to compute the wavelength at the source first and use *that* number, but that requires you know the speed of the source. My method doesn't require it. So as to avoid arguments of relativity I've been talking about sound waves here where the frequency change is different depending on whether the source moves towards the receiver or vice versa. Well, I did qualify it by saying for a given value of C, the relationship of frequency to wavelength is fixed, and that is correct. :-) It would appear that either I was mistakenly arguing EM Doppler shift where relative velocity is what matters, or acoustic Doppler shift works a bit differently in Russia. *LOL* All the references I could find where the source was moving stated that it was relative velocity that mattered, not which was in motion, but now it's obvious that they were refering to EM Doppler. Simply stated, your reference says that, with acoustic Doppler shift, when the source is moving, the wavelength observed by the receiver changes, but when the receiver is moving, C, the speed of propagation in the medium, as it is observed by the receiver changes. Sounds logical to me, and it certainly isn't the first time I've made a mistake. I suppose that means that, when both are moving, both wavelength and C change, but all changes are relative to the receiver's perception. Relative to the source, neither changes. :-) |
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Bob Cain wrote: RP wrote: Time, when a universal standard is adopted for use by all observers, whether or not on board clocks perpetually agree with that standard, must necessarily be universal time. Obvious why, eh? Nope. That implies a preferred reference frame and there isn't one. LOL. Well it isn't a mysterious undertaking; the preferred frame would be exactly the one that we preferred, i.e. upon which we agreed. The point is, that any clock in equilibrium will do, as these, regardless of actual ticking rate, will tick at proportional rates to each other. Certainly you can find no preferred frame, in the sense that you implied, if all observers were to use the Earth/Sun orbital system as reference clock. The ambiguities that you have in mind are relevant only in the special relativistic view of simultaneity. It isn't difficult to see that even within the Galilean system, that the redefinition of time to: What an observers clock reads, also leads to a transform other then the Galilean transform, even though it will necessarily derive the same outcomes, that is, since we've not altered the physics of space time with our redefinition of measures. Thus, show me in a quantitative fashion that Newtonian Mechanics makes an incorrect prediction within its domain of applicability, i.e. the kinematics of neutral masses. If you can do so without utilizing a premise that he did not actually pen, then good luck. Don't try Fizeau's measurements of light speed in moving media, because I've embarrassed enough Ph D's already in that argument by showing them how to correctly compose "average speeds" with the Galilean transform I can't. Don't have the Principia at hand. :-) This will do: F = dp/dt E = 0.5mv^2 Galilean transform Energy is conserved. Angular momentum is conserved. That's about all there is to Newton, barring his gravitation equation, which one could argue is simply incomplete. Even so, within experimental error, his equation hasn't been disproved. Any deviations can be corrected for within the context of the premises listed above, or by the inclusion of extraneous electromagnetic forces, which latter are not necessarily contradictory to Newton, as I've proved also by formulating just such an electromagnetic synthesis. This argument has a high prospect of degrading into philosophical banter, and with good reason, it began that way I'll leave it with this: They are disjoint logical systems, bottom line. Richard Perry http://www.cswnet.com/~rper/Electromagnetism.html Bob |
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"Porky" wrote in message
.. . Simply stated, your reference says that, with acoustic Doppler shift, when the source is moving, the wavelength observed by the receiver changes, Not quite. I think I see where your practical experience, which I lack, is throwing you off. You think of wavelength solely as W=C/F. In practical terms such as figuring out horn length, loudspeaker dimensions, room acoustics, and so forth, that works fine because everything is stationary. In effect you're saying that wavelength is the distance the second wave travels after the receiver encounters the first wave. However, wavelength by definition is the distance between the crest or peak of one wave and the peak/crest of the next wave. Wavelength is a distance. We can stop time and motion and figure out the wavelength with a ruler. Distance is time independent (Los Angeles and New York are 3,000 miles apart last night, tonight and tomorrow). W=C/F is a quick way of calculating wavelength if everything is stationary. But it's not the *definition*. Again, since the above practical examples require things to be stationary, it's easy to fall into the trap of thinking of it that way. When the source emits a wave, moves, then emits the second wave, the distance is different than if the source had just stood still. If the receiver is still, it can use W=C/F to figure out the wavelength. If the receiver is moving, W=C/F has to include an adjustment to C to calculate the distance between the crest/peak of one wave and the crest/peak of the next wave. Simply stated it's the distance the second wave traveled plus or minus the distance the receiver traveled as opposed to just the distance traveled by itself. Saying the apparent or "observed" wavelength changes when the source moves is incorrect. It really is different. When the receiver moves you might say that the "observed" wavelength is different, but that again implies that wavelength is the distance the second wave travels after the receiver encounters the first wave, which we know it's not. We can't use W=C/F if the receiver is moving - we use W=(C+/-V)/F where V is the velocity of the receiver relative to the source. |
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"RP" wrote in message
... LOL. Well it isn't a mysterious undertaking; the preferred frame would be exactly the one that we preferred, i.e. upon which we agreed. The point is, that any clock in equilibrium will do, as these, regardless of actual ticking rate, will tick at proportional rates to each other. Certainly you can find no preferred frame, in the sense that you implied, if all observers were to use the Earth/Sun orbital system as reference clock. The ambiguities that you have in mind are relevant only in the special relativistic view of simultaneity. Is that why somebody can post a message in this newsgroup from New York at midnight and I see it here in Phoenix at 9:00 pm?? |
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"Jim Carr" wrote in message news:g%Kad.29368$_a3.1912@fed1read05...
"Jim Greenfield" wrote in message om... Porky should realise at once that you haven't given him sufficient information (your speed ref the room). As he doesn't understand the implications of mistakenly identifying the _cause_ of Doppler, he might fall for the trap! :-) Jim G c'=c+v Aw, you're no fun!! To recap this entire discussion, it started like this. Porky described Doppler for sound as a shift in the wavelength whether the source or receiver is moving (one should describe it using frequency of the receiver IMHO). I replied that the wavelength certainly does change when the source moves, but it does NOT change when only the receiver moves. It seems to me my bike sounds the same at 5000rpm in the shed, or when I am on it at 120 kliks! Though to someone I am approaching, they would think I am pulling (roughly) 6000rpm He said I was wrong because wavelength and frequency are always in a direct relationship to one another. Nope. Frequency is "actions at a POINT per time". I despair at the inability of people to grasp this seemingly simple concept. If the point is moving, things alter (relative speed/frequency/sine waves passed per second) He cited a few references that did not explicitly discuss the movement of the receiver *and* wavelength specifically. I didn't care because it seemed readily obvious to my uneducated mind. I decided to find a link that discusses wavelength: http://physics.nad.ru/Physics/English/dopp_txt.htm . This site writes, "Next, we shall consider the case when observer moves and the source of the wave is still. In this case the wavelength is NOT changed and Doppler frequency shift appears because the velocity w of the wave relatively the observer is changed." That is certainly a good way of explaining it (which is how you did as well). I never said it that way. My little formula certainly worked that way, but I should have used the phrase "the velocity of the wave relative to the observer is changed." No matter how you slice it if you observe a sound frequency while you're moving, you need to account for that movement when calculating wavelength. You could use Doppler to try to compute the wavelength at the source first and use *that* number, but that requires you know the speed of the source. My method doesn't require it. So as to avoid arguments of relativity I've been talking about sound waves here where the frequency change is different depending on whether the source moves towards the receiver or vice versa. Drat! I was coming to the Rel bit. It always comes up in discussion of Doppler, because DHR's like to compare sound waves with light. I don't think there is any correllation between light (photons through a vacuum) and sound (pressure fronts through a medium, but there you go! YOU realise that those waves in the hall aren't actually changing their wavelength when you move towards them, but try explaining to a DHR that a stream of photons will have a changed 'frequency' of hitting a receiver, WITHOUT having an altered wavelength (distance between them), if the source or observer are moving rel each other. Sorry to spoil your fun :-) There are plenty more who think that Doppler is a cause, instead of an effect. Jim G c'=c+v |
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"Jim Greenfield" wrote in message
om... Drat! I was coming to the Rel bit. It always comes up in discussion of Doppler, because DHR's like to compare sound waves with light. I don't think there is any correllation between light (photons through a vacuum) and sound (pressure fronts through a medium, but there you go! YOU realise that those waves in the hall aren't actually changing their wavelength when you move towards them, but try explaining to a DHR that a stream of photons will have a changed 'frequency' of hitting a receiver, WITHOUT having an altered wavelength (distance between them), if the source or observer are moving rel each other. In case you missed it before, I am entirely untrained in this field. It's not even a hobby. I play and record music as a hobby, but it doesn't require knowing any of this stuff. With that said... Looking at a formula I found for determing Doppler in electromagnetic waves I see it is different than for sound. Looking at *that* formula I would have to say that it doesn't matter if the source or observer is moving, you'll see the same apparent shift in frequency. With Doppler in sound, if the source is moving at X you get a different frequency shift than if you do if the observer is moving at X (assuming a head-on movement). With electromagnetic waves I would hazard to guess that the "actual" wavelength changes in either case (source or observer moving) since the speed of light is my speed limit. Or maybe I'm falling into a layman's trap. If so, I'm sure someone will correct me. Sorry to spoil your fun :-) There are plenty more who think that Doppler is a cause, instead of an effect. Very well put. |
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"Jim Carr" wrote in message news:Fh2bd.29584$_a3.17034@fed1read05... "Porky" wrote in message .. . Simply stated, your reference says that, with acoustic Doppler shift, when the source is moving, the wavelength observed by the receiver changes, Not quite. I think I see where your practical experience, which I lack, is throwing you off. You think of wavelength solely as W=C/F. In practical terms such as figuring out horn length, loudspeaker dimensions, room acoustics, and so forth, that works fine because everything is stationary. In effect you're saying that wavelength is the distance the second wave travels after the receiver encounters the first wave. Actually, I was referring to the apparent wavelength that the receiver "sees", the actual wavelength does not change, but the wavelength as it appears to the receiver isn't the same as the actual wavelength. However, wavelength by definition is the distance between the crest or peak of one wave and the peak/crest of the next wave. Wavelength is a distance. We can stop time and motion and figure out the wavelength with a ruler. Distance is time independent (Los Angeles and New York are 3,000 miles apart last night, tonight and tomorrow). W=C/F is a quick way of calculating wavelength if everything is stationary. But it's not the *definition*. Again, since the above practical examples require things to be stationary, it's easy to fall into the trap of thinking of it that way. When the source emits a wave, moves, then emits the second wave, the distance is different than if the source had just stood still. If the receiver is still, it can use W=C/F to figure out the wavelength. If the receiver is moving, W=C/F has to include an adjustment to C to calculate the distance between the crest/peak of one wave and the crest/peak of the next wave. Simply stated it's the distance the second wave traveled plus or minus the distance the receiver traveled as opposed to just the distance traveled by itself. But as it appears to the receiver, the apparent wavelength will be longer or shorter, depending on direction of motion. This doesn't change the actual wavelength of course. Saying the apparent or "observed" wavelength changes when the source moves is incorrect. It really is different. When the receiver moves you might say that the "observed" wavelength is different, but that again implies that wavelength is the distance the second wave travels after the receiver encounters the first wave, which we know it's not. We can't use W=C/F if the receiver is moving - we use W=(C+/-V)/F where V is the velocity of the receiver relative to the source. According to the link you posted, if the source is moving, the apparent wavelength changes, but if the receiver is moving C, the apparent speed of sound changes. Therefore, F=C/W always applies in the general sense, the difference is that if the source is moving, W is the variable, and if the receiver is moving, C is the variable. Your equation above is correct and it calculates the change in apparent C if the receiver is moving. Correct me if I'm wrong, but won't Frc = Ftx ((C + V)/C) work for motion of either Tx or Rc? V, of course, will be a positive number if the motion is toward the other and a negative number if the motion is away from the other. The trick is that whether W or C is the variable depends on which is moving, the source or the receiver. This doesn't take the variation of velocity/time into account, but for the home studioist, that can safely be ignored. |
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"Jim Carr" wrote in message news:rZ3bd.29612$_a3.12325@fed1read05... "Jim Greenfield" wrote in message om... Drat! I was coming to the Rel bit. It always comes up in discussion of Doppler, because DHR's like to compare sound waves with light. I don't think there is any correllation between light (photons through a vacuum) and sound (pressure fronts through a medium, but there you go! YOU realise that those waves in the hall aren't actually changing their wavelength when you move towards them, but try explaining to a DHR that a stream of photons will have a changed 'frequency' of hitting a receiver, WITHOUT having an altered wavelength (distance between them), if the source or observer are moving rel each other. In case you missed it before, I am entirely untrained in this field. It's not even a hobby. I play and record music as a hobby, but it doesn't require knowing any of this stuff. With that said... Looking at a formula I found for determing Doppler in electromagnetic waves I see it is different than for sound. Looking at *that* formula I would have to say that it doesn't matter if the source or observer is moving, you'll see the same apparent shift in frequency. With Doppler in sound, if the source is moving at X you get a different frequency shift than if you do if the observer is moving at X (assuming a head-on movement). With electromagnetic waves I would hazard to guess that the "actual" wavelength changes in either case (source or observer moving) since the speed of light is my speed limit. Or maybe I'm falling into a layman's trap. If so, I'm sure someone will correct me. When dealing with relativistic speeds you not only have C, W and F to contend with, the time contraction factor Tau comes into play and at any velocity which is a respectable percentage of the speed of light, Tau must be taken into account to get accurate results. For the home recordist who just wants to figure acoustic Doppler shift, Tau is insignificant. |
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"Jim Carr" wrote in message news:rZ3bd.29612$_a3.12325@fed1read05...
"Jim Greenfield" wrote in message om... Drat! I was coming to the Rel bit. It always comes up in discussion of Doppler, because DHR's like to compare sound waves with light. I don't think there is any correllation between light (photons through a vacuum) and sound (pressure fronts through a medium, but there you go! YOU realise that those waves in the hall aren't actually changing their wavelength when you move towards them, but try explaining to a DHR that a stream of photons will have a changed 'frequency' of hitting a receiver, WITHOUT having an altered wavelength (distance between them), if the source or observer are moving rel each other. In case you missed it before, I am entirely untrained in this field. It's not even a hobby. I play and record music as a hobby, but it doesn't require knowing any of this stuff. With that said... Me too! until I had my left fingers chopped!!!!!!!!!!!!! With that said......... Looking at a formula I found for determing Doppler in electromagnetic waves I see it is different than for sound. Looking at *that* formula I would have to say that it doesn't matter if the source or observer is moving, you'll see the same apparent shift in frequency. With Doppler in sound, if the source is moving at X you get a different frequency shift than if you do if the observer is moving at X (assuming a head-on movement). Are you sure? If I am on my bike at 5000rpm, and my mate behind is pulling the same, it sounds just the same as if we are both stationary; his motion (source) has not effected the frequency to me, but we will both sound to be pulling 6000 to someone standing by the road ahead. You must measure the wavelength from where it is produced relative to the medium, and not to the source, in the case of sound in air. If the source were moving at 1/2 speed of sound (same direction), you should still measure the wavelength from where it was produced (coordinate in the air), to where it is after one cycle. This is confusing for longituudinal waves, but just think in terms of cycles (points on a sine) So I don't think that wavelength alters in either case relative to the medium against which I am hearing(measuring) With electromagnetic waves I would hazard to guess that the "actual" wavelength changes in either case (source or observer moving) since the speed of light is my speed limit. Or maybe I'm falling into a layman's trap. If so, I'm sure someone will correct me. Sorry to spoil your fun :-) There are plenty more who think that Doppler is a cause, instead of an effect. Very well put. Thanks Jim G c'=c+v |
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"Porky" wrote in message ...
"Jim Carr" wrote in message news:rZ3bd.29612$_a3.12325@fed1read05... "Jim Greenfield" wrote in message om... Drat! I was coming to the Rel bit. It always comes up in discussion of Doppler, because DHR's like to compare sound waves with light. I don't think there is any correllation between light (photons through a vacuum) and sound (pressure fronts through a medium, but there you go! YOU realise that those waves in the hall aren't actually changing their wavelength when you move towards them, but try explaining to a DHR that a stream of photons will have a changed 'frequency' of hitting a receiver, WITHOUT having an altered wavelength (distance between them), if the source or observer are moving rel each other. In case you missed it before, I am entirely untrained in this field. It's not even a hobby. I play and record music as a hobby, but it doesn't require knowing any of this stuff. With that said... Looking at a formula I found for determing Doppler in electromagnetic waves I see it is different than for sound. Looking at *that* formula I would have to say that it doesn't matter if the source or observer is moving, you'll see the same apparent shift in frequency. With Doppler in sound, if the source is moving at X you get a different frequency shift than if you do if the observer is moving at X (assuming a head-on movement). With electromagnetic waves I would hazard to guess that the "actual" wavelength changes in either case (source or observer moving) since the speed of light is my speed limit. Or maybe I'm falling into a layman's trap. If so, I'm sure someone will correct me. When dealing with relativistic speeds you not only have C, W and F to contend with, the time contraction factor Tau comes into play and at any velocity which is a respectable percentage of the speed of light, Tau must be taken into account to get accurate results. For the home recordist who just wants to figure acoustic Doppler shift, Tau is insignificant. Jim Carr: As I intimated, Porky, as a believing DHR, has stepped up to the plate equipped with the standard SR opening play. Just because you are a layman (as am I), don't be coerced into accepting something (Relativity), which is patently impossible/wrong, just because it is in fashion (they can get their stuff "peer reviewed" by OTHER true believers). As you realise, there are three things involved; velocity, wavelength, frequency. Notice immediately Relativity is introduced, Porky introduces a fourth! Tau What Porky fails to mention, is that this is the result of circular logic which runs like this: c (velocity of light in vacuum) is a constant, independent of the velocity of the source of the light. Due to this magic, length contracts as c is approached time dilates (changes) as c is approached Because time and length both change, c remains the same! Do you think at school you could get away with that? Given a simple 3 part algebra, with 2 unknowns, provide an accepted answer by throwing in an extra (arbitrary and imaginary) factor?????? Relativity will go down in history as the greatest con of the 20th century. (It surely wont see this one out) Jim G c'=c+v |
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