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#1
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acoustics
A few days ago, I was in a room on the third floor, the
window was open, some people were conversating down at street level. Their words came in, clear as a bell, almost like being in the same room. I was surprised, I thought the power would attenuate a lot faster. Then I wondered if it also works the other way - could they hear our conversations, just as crisp? I recall a discussion of optics, and someone remarked: 'I see you, you see me' is pretty much a universal law. Does that also hold for acoustics? -- Rich |
#2
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acoustics
Rich,
'I see you, you see me' is pretty much a universal law. Does that also hold for acoustics? If someone is in front of a big "satellite dish" their speaking will be focused toward you, and the dish will also collect sound from you and focus it at them. The pattern will be highly directional, but it seems to me this is indeed a reversible situation. --Ethan |
#3
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acoustics
If they were having a conversation, they were conversing, not
conversating. |
#4
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acoustics
On Tue, 25 Dec 2007 09:34:20 -0500, "Ethan Winer" ethanw at
ethanwiner dot com wrote: Rich, 'I see you, you see me' is pretty much a universal law. Does that also hold for acoustics? If someone is in front of a big "satellite dish" their speaking will be focused toward you, and the dish will also collect sound from you and focus it at them. The pattern will be highly directional, but it seems to me this is indeed a reversible situation. This is the same example I was going to use, but with the opposite result: The dish (parabolic reflector) focuses incoming parallel waves to a point. If you put a point source at the focus, then the output is a collimated beam. That's how headlight/flashlight reflectors work. The output is not "focused" in the same sense as when the dish is used as a collector, since there is no place where the rays/waves focus to a point (assuming an ideal parabolic reflector). So in answer to the original question, the "I see you, you see me" holds, in the sense that the process is not totally unidirectional, but the efficiencies or sensitivities in each direction can be quite different. Best regards, Bob Masta DAQARTA v3.50 Data AcQuisition And Real-Time Analysis www.daqarta.com Scope, Spectrum, Spectrogram, FREE Signal Generator Science with your sound card! |
#5
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acoustics
"BobG" wrote in message ... : If they were having a conversation, they were conversing, not : conversating. On the other hand, there are five metacarpals. The other side of the coin is the obverse, not the reverse or the converse. :-) |
#6
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acoustics
On Dec 25, 4:53*am, RichD wrote:
A few days ago, I was in a room on the third floor, the window was open, some people were conversating down at street level. *Their words came in, clear as a bell, almost like being in the same room. *I was surprised, I thought the power would attenuate a lot faster. Then I wondered if it also works the other way - could they hear our conversations, just as crisp? I recall a discussion of optics, and someone remarked: 'I see you, you see me' is pretty much a universal law. Does that also hold for acoustics? -- Rich Beware generalization. One could easily come up with a scenario in which sound propagates between two points with more attenuation in one direction. Imagine a New York City deli owner closes up for the night. He pulls down the sheet metal gate and retreats to the back of his store. A friend comes up, puts his face six inches from the sheet metal barrier and says something to the owner inside store, not yelling, just raising his voice somewhat above conversational level. Having his mouth right up against the gate causes the sheet metal to vibrate and transmits the sounds inside the store. In the quiet of the store owner can hear every syllable. The store owner, standing in the cat food and paper goods aisle 16 feet from the sheet metal gate, responds. As humans are wont to do when speaking, he uses the same tone of voice. Of course, by the time the sound of his voice reaches the sheet metal surface sixteen feet away it softens by a factor of a thousand compared to the power other guy's voice hit the metal with. Not enough to overcome the damping of the hinges between the segments of the sheetmetal gate. His friend can hardly hear his voice, let alone make out the words. Also, consider that the deli owner's friend is standing out in a street surrounded by noises: traffic sounds, breezes blowing, people talking. The whisper of a sound coming through the metal gate into the noisy environment has such a low SNR that the friend standing outside is lucky to hear anything at all. It's still a crapshoot when highly trained architects and engineers design a modern concert hall whether it will have any good acoustics at all. Some of the best halls were designed generations ago using a seat-of-the pants, intuitive approach. Acoustics are notoriously unpredictable. |
#7
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acoustics
RichD wrote:
A few days ago, I was in a room on the third floor, the window was open, some people were conversating down at street level. Their words came in, clear as a bell, almost like being in the same room. I was surprised, I thought the power would attenuate a lot faster. Then I wondered if it also works the other way - could they hear our conversations, just as crisp? I recall a discussion of optics, and someone remarked: 'I see you, you see me' is pretty much a universal law. Does that also hold for acoustics? I think it does, but only if the radiation pattern is also reversed. For example, if someone stands at the focus of a parabolic reflector, it very efficiently captures the radial sound waves from their voice and produces a nearly plane wave radiation pattern that travels long distances with little dispersion. In effect, the parabola converts the near center radial wave pattern to a far center radial pattern (the waves act as if their center of radiation is a lot further away than the speaker actually is) so the square law attenuation rule still applies, but getting to twice the distance to have wave strength fall to 1/4 means getting a lot further away. Now, think of this acting in reverse. Your voice radiates in a spherical wave, so falls by square law, from your mouth. Only a small fraction of that sphere is collected by the parabola to reach its focus. The non-reversibility is not the fault of the parabola, but your fault for not radiating a reverse spherical wave pattern similar to what you received. That kind of wave front would return to the parabola and focus almost perfectly reversibly to the one you received. Now, if you add another parabola at your location, you will send almost plane waves (spherical waves as if the center were far from you), almost the reverse of what you received. Replace both parabola with ellipsoids and the reversibility is even better. -- Regards, John Popelish |
#8
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acoustics
BobG wrote:
If they were having a conversation, they were conversing, not conversating. Oh, that sounds so perverse! -- "I'd rather have a bottle in front of me than a frontal lobotomy" "Daily Thought: SOME PEOPLE ARE LIKE SLINKIES. NOT REALLY GOOD FOR ANYTHING BUT THEY BRING A SMILE TO YOUR FACE WHEN PUSHED DOWN THE STAIRS. http://webpages.charter.net/jamie_5" |
#9
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acoustics
"Jamie" t wrote in message ... : BobG wrote: : : If they were having a conversation, they were conversing, not : conversating. : Oh, that sounds so perverse! I'm not conversant with that term. Please do not be so perversitative, conversate properly. |
#10
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acoustics
On Tue, 25 Dec 2007, RichD wrote:
A few days ago, I was in a room on the third floor, the window was open, some people were conversating down at street level. Their words came in, clear as a bell, almost like being in the same room. I was surprised, I thought the power would attenuate a lot faster. Then I wondered if it also works the other way - could they hear our conversations, just as crisp? I recall a discussion of optics, and someone remarked: 'I see you, you see me' is pretty much a universal law. Does that also hold for acoustics? How well does "I see you, you see me" hold for a telescope? The optical system is reversible, but that doesn't mean that both ends are equal. In your example, it sounds like reflection from the next building and the open windows. Your noise that reflects downwards from the open windows will make it to street level, but since your room is likely to be quieter than street level, you're probably talking more quietly than the people on the street. -- Timo Nieminen - Home page: http://www.physics.uq.edu.au/people/nieminen/ E-prints: http://eprint.uq.edu.au/view/person/...,_Timo_A..html Shrine to Spirits: http://www.users.bigpond.com/timo_nieminen/spirits.html |
#11
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acoustics
RichD wrote:
A few days ago, I was in a room on the third floor, the window was open, some people were conversating down at street level. Their words came in, clear as a bell, almost like being in the same room. I was surprised, I thought the power would attenuate a lot faster. Then I wondered if it also works the other way - could they hear our conversations, just as crisp? I recall a discussion of optics, and someone remarked: 'I see you, you see me' is pretty much a universal law. Does that also hold for acoustics? Whispering galleries and inside elliptic reflectors, yes. This is the preferred way to build confessionals in church - at one focus - with rentable scholarship rooms at the other focus. Parabolic reflector (satellite dish), not so much. Incoming will be focused but outgoing will be collimated. -- Uncle Al http://www.mazepath.com/uncleal/ (Toxic URL! Unsafe for children and most mammals) http://www.mazepath.com/uncleal/lajos.htm#a2 |
#12
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acoustics
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#13
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acoustics
I recall a discussion of optics, and someone remarked: 'I see you, you see me' is pretty much a universal law. Does that also hold for acoustics? Wind direction may have an effect on sound but not on light. Not true for light anyway. What about one-way mirrors? Ian |
#14
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acoustics
In , Ian Iveson wrote:
I recall a discussion of optics, and someone remarked: 'I see you, you see me' is pretty much a universal law. Does that also hold for acoustics? Wind direction may have an effect on sound but not on light. Not true for light anyway. What about one-way mirrors? One-way mirrors are actually not directional. They are mostly reflective and slightly transmissive, and installed between rooms with greatly different illumination levels. If you flip the mirror around, the effect of that "partially silvered" surface will not change. - Don Klipstein ) |
#15
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acoustics
"RichD" A few days ago, I was in a room on the third floor, the window was open, some people were conversating down at street level. Their words came in, clear as a bell, almost like being in the same room. I was surprised, I thought the power would attenuate a lot faster. Then I wondered if it also works the other way - could they hear our conversations, just as crisp? ** Almost certainly not. I recall a discussion of optics, and someone remarked: 'I see you, you see me' is pretty much a universal law. Does that also hold for acoustics? ** It ain't true of optics or acoustics. Egs. A peep hole device allows you to see who is outside your door while being unobserved, similarly a periscope or telescope allows an observer to be unseen. A small hole in a wall of a room will allow you to hear what is happening outside if you press your ear against it - however, very little of your voice energy escapes the room through that hole. ....... Phil |
#16
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acoustics
On Tue, 25 Dec 2007 11:08:38 -0500, John Popelish
wrote: Now, if you add another parabola at your location, you will send almost plane waves (spherical waves as if the center were far from you), almost the reverse of what you received. The Sante Fe, NM Childrens Museum has a wonderful outdoor example of this. Two parabolic dishes, doubtlessly C-band castoffs, face each other across an open space of maybe fifty feet, centers at a young person's head height. In front of each dish is a post-mounted yoke, into which you place your chin. Back-to-back conversation, outdoors, at about fifty feet and normal conversational volume - it's big fun. Much thanks, Chris Hornbeck |
#17
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acoustics
Bob,
The output is not "focused" in the same sense as when the dish is used as a collector Yes, but the person away from the collector isn't a "large" source either. So it still seems it would be 100 percent reciprocal, no? This is like half of a pair of reflectors like you see in parks, where two people can be hundreds of yards away and talk as if they're next to each other. --Ethan |
#18
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acoustics
On Tue, 25 Dec 2007 09:34:20 -0500, "Ethan Winer" ethanw at
ethanwiner dot com wrote: Rich, 'I see you, you see me' is pretty much a universal law. Not if I'm in the dark, and you're in the sun. Or if I'm hiding in the bushes and you're not. Or if I have a telescope but you don't. John |
#19
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acoustics
"RichD" wrote in message
A few days ago, I was in a room on the third floor, the window was open, some people were conversating down at street level. Their words came in, clear as a bell, almost like being in the same room. I was surprised, I thought the power would attenuate a lot faster. Then I wondered if it also works the other way - could they hear our conversations, just as crisp? I recall a discussion of optics, and someone remarked: 'I see you, you see me' is pretty much a universal law. Does that also hold for acoustics? Yes, acoustical reciprocity exists. |
#20
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acoustics
On Tue, 25 Dec 2007 15:30:57 +0000, Androcles wrote:
"BobG" wrote in message : If they were having a conversation, they were conversing, not : conversating. On the other hand, there are five metacarpals. The other side of the coin is the obverse, not the reverse or the converse. :-) No, actually, the obverse is the "front" of the coin, usually considered to be "heads", and the "tails" side is the reverse. Hope This Helps! Rich |
#21
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acoustics
In article , John Larkin wrote:
On Tue, 25 Dec 2007 09:34:20 -0500, "Ethan Winer" ethanw at ethanwiner dot com wrote: Rich, 'I see you, you see me' is pretty much a universal law. Not if I'm in the dark, and you're in the sun. Or if I'm hiding in the bushes and you're not. Or if I have a telescope but you don't. I thought this refers to a principle that when a ray is traced from origin to destination, percentage loss at each lossy point are the same in both directions, percentage reflected by partially reflective objects in the way is the same for both directions, and percentage making it from origin to destination are the same in both directions. Of course, polarizers and polarized light can complicate this, but we can't have a situation where there is a container that light can enter but not exit along the same path in a way that allows a thermal radiator to heat a target in the container to a higher temperature than the thermal radiator is at. - Don Klipstein ) |
#22
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acoustics
"Rich Grise" wrote in message news:HGAcj.83626$GV4.20532@trnddc05... : On Tue, 25 Dec 2007 15:30:57 +0000, Androcles wrote: : "BobG" wrote in message : : : If they were having a conversation, they were conversing, not : : conversating. : : On the other hand, there are five metacarpals. The other side of the : coin is the obverse, not the reverse or the converse. :-) : : No, actually, the obverse is the "front" of the coin, usually considered : to be "heads", and the "tails" side is the reverse. : : Hope This Helps! No, in fact, observe the other side is the inside and conversely has a reversed head on the reverse and a converse tail on the reverse of the obverse. Hope that is declarified. |
#23
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acoustics
Androcles wrote:
"Rich Grise" wrote in message news:HGAcj.83626$GV4.20532@trnddc05... : On Tue, 25 Dec 2007 15:30:57 +0000, Androcles wrote: : "BobG" wrote in message : : : If they were having a conversation, they were conversing, not : : conversating. : : On the other hand, there are five metacarpals. The other side of the : coin is the obverse, not the reverse or the converse. :-) : : No, actually, the obverse is the "front" of the coin, usually considered : to be "heads", and the "tails" side is the reverse. : : Hope This Helps! No, in fact, observe the other side is the inside and conversely has a reversed head on the reverse and a converse tail on the reverse of the obverse. Hope that is declarified. They do have pills for what ails you. In the mean time: stay calm. |
#24
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acoustics
"Sjouke Burry" wrote in message ... : Androcles wrote: : "Rich Grise" wrote in message : news:HGAcj.83626$GV4.20532@trnddc05... : : On Tue, 25 Dec 2007 15:30:57 +0000, Androcles wrote: : : "BobG" wrote in message : : : : : If they were having a conversation, they were conversing, not : : : conversating. : : : : On the other hand, there are five metacarpals. The other side of the : : coin is the obverse, not the reverse or the converse. :-) : : : : No, actually, the obverse is the "front" of the coin, usually considered : : to be "heads", and the "tails" side is the reverse. : : : : Hope This Helps! : : No, in fact, observe the other side is the inside and conversely : has a reversed head on the reverse and a converse tail on : the reverse of the obverse. : Hope that is declarified. : : : They do have pills for what ails you. : In the mean time: stay calm. Nah, I just ignore ****headed trolls like you that are not amused by a simple play on words you are incapable of understanding and rely on insult for their kicks. **** off, you ****ing moron. *plonk* |
#25
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acoustics
On Wed, 26 Dec 2007 09:01:06 -0500, "Ethan Winer" ethanw at
ethanwiner dot com wrote: Bob, The output is not "focused" in the same sense as when the dish is used as a collector Yes, but the person away from the collector isn't a "large" source either. So it still seems it would be 100 percent reciprocal, no? This is like half of a pair of reflectors like you see in parks, where two people can be hundreds of yards away and talk as if they're next to each other. You have given the answer in your example: If one reflector was all it took to get 100% reciprocal operation, then they wouldn't use two reflectors. Suppose we think of this with light beams instead of sound waves, and use laser pointers so that we have a planar wave front. The guy without a reflector can aim his beam at the distant reflector, which might have an area of (say) 10 square feet, and anywhere he aims within that area the beam will be captured and received more-or-less 100% at the focal point. But the guy at the focal point can't do the same thing in reverse. He either needs to aim his beam *exactly* at the other guy (avoiding the reflector, or bouncing it on a careful trajectory), or else he needs many, many beams at slightly different trajectories so that they will cover the same 10 square-foot area at full intensity at the reflectorless guy's end. Best regards, Bob Masta DAQARTA v3.50 Data AcQuisition And Real-Time Analysis www.daqarta.com Scope, Spectrum, Spectrogram, FREE Signal Generator Science with your sound card! |
#26
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acoustics
Bob,
If one reflector was all it took to get 100% reciprocal operation, then they wouldn't use two reflectors. I don't think that follows. With only one reflector, the gain would be insufficient for EITHER person to hear the other. Again, I'm not arguing too strongly because I don't really know for sure. But so far I can't see why it's not reciprocal. The guy without a reflector can aim his beam at the distant reflector, which might have an area of (say) 10 square feet, and anywhere he aims within that area the beam will be captured and received more-or-less 100% at the focal point. Yes, but a person talking is not a beam. --Ethan |
#28
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acoustics
"John Larkin" wrote in message ... On Wed, 26 Dec 2007 23:20:18 +0000 (UTC), (Don Klipstein) wrote: In article , John Larkin wrote: On Tue, 25 Dec 2007 09:34:20 -0500, "Ethan Winer" ethanw at ethanwiner dot com wrote: Rich, 'I see you, you see me' is pretty much a universal law. Not if I'm in the dark, and you're in the sun. Or if I'm hiding in the bushes and you're not. Or if I have a telescope but you don't. I thought this refers to a principle that when a ray is traced from origin to destination, percentage loss at each lossy point are the same in both directions, percentage reflected by partially reflective objects in the way is the same for both directions, and percentage making it from origin to destination are the same in both directions. Of course, polarizers and polarized light can complicate this, but we can't have a situation where there is a container that light can enter but not exit along the same path in a way that allows a thermal radiator to heat a target in the container to a higher temperature than the thermal radiator is at. - Don Klipstein ) There are optical isolators, like electrical isolators, that let light go from port A to port B, but block light from B to A. They violate no laws of thermodynamics, because they absorb the light from B, rather than reflecting it. http://en.wikipedia.org/wiki/Optical_isolator Or just watch them interviewing the suspects on Law & Order :-) |
#29
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acoustics
On Thu, 27 Dec 2007 11:51:39 -0500, "Ethan Winer" ethanw at
ethanwiner dot com wrote: Bob, If one reflector was all it took to get 100% reciprocal operation, then they wouldn't use two reflectors. I don't think that follows. With only one reflector, the gain would be insufficient for EITHER person to hear the other. Again, I'm not arguing too strongly because I don't really know for sure. But so far I can't see why it's not reciprocal. The guy without a reflector can aim his beam at the distant reflector, which might have an area of (say) 10 square feet, and anywhere he aims within that area the beam will be captured and received more-or-less 100% at the focal point. Yes, but a person talking is not a beam. The reflector provides gain for the listener, by concentrating the sound from a large area down to a small area at his ear. Let's say that the reflector is 10 square feet, so all sound impinging on that area is concentrated down to his ear due to the nature of the parabolic shape. The gain of this operation could easily be 100:1 if the ear catches only 0.1 square foot. Now when we turn around and speak into the reflector it *spreads* the sound from the small source (mouth) over that same 10 square feet. Is there gain here? Yes, but not the same as the prior case: Here the only gain (as far as the guy at the other end without a reflector is concerned) is due to the fact that without the reflector the sound would be a spherical source from the mouth, falling off with the square of distance. With the reflector, assuming everything was just right, the best you could hope for would be sound that was collimated into a plane wave that did not fall off with distance. But the sound would still be spread over 10 square feet in the ideal case, and much more in reality. The ear of the listener on the other end only catches a tiny percent of that without a reflector. If his ear only catches 0.1 square foot, there is a *loss* of 100:1 compared to having a reflector. Best regards, Bob Masta DAQARTA v3.50 Data AcQuisition And Real-Time Analysis www.daqarta.com Scope, Spectrum, Spectrogram, FREE Signal Generator Science with your sound card! |
#30
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acoustics
Bob,
Let's say that the reflector is 10 square feet, so all sound impinging on that area is concentrated down to his ear due to the nature of the parabolic shape. The gain of this operation could easily be 100:1 if the ear catches only 0.1 square foot. Yes, but my point is that the source / person is not 10 square feet! --Ethan |
#31
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acoustics
On Dec 28, 10:46 am, "Ethan Winer" ethanw at ethanwiner dot com
wrote: Bob, Let's say that the reflector is 10 square feet, so all sound impinging on that area is concentrated down to his ear due to the nature of the parabolic shape. The gain of this operation could easily be 100:1 if the ear catches only 0.1 square foot. Yes, but my point is that the source / person is not 10 square feet! So far, everyone is making a bunch of assumptions, many of which simply don't hold, with the result being that the conclusions people are reaching are HIGHLY suspect. For example: 1. A parbolic reflector, has TWO focal points. If the source or receiver is placed at the principle focal point, the other focal point is an infinite distance away and the system then will focus an incoming set of parallel rays to the focal point and vice versa. Move the focal point farther from the principle point, and the other focal point now moves closer to the system and the incoming/outgoing rays are no longer parallel, but convergent. Asserting that a parabolic disk will focus a set of parallel rays to a small point ASSUME that the source or receiver is placed at the infinity focus point of the parabola. A reciprocal transmitter-receiver system would consist of two parabolic reflectors, with the transmitter and receiver placed at the principle focus of each reflector. The transmitter would emit a parallel bundle of rays which the receiver could refocus back to the focal point again. BUT, a system does not REQUIRE a reciprocal physical arrangement. You could have, say, a transmitter with no reflector placed 100 feet away and a receiver with its reflectors aimed at it and the receiver moved out somewhat to compensate. 2. The ability of any such system to focus to a small point is a function of the size of the reflector and the wavelengths involved. With a reflector a few FEET in diameter and wavelengths ranging from several inches to many feet, the efficacy of a parabolic reflector is limited. At low frequencies where the wavelength is large compared to the dish, it simply doesn't focus anything. At higher frequencies and thus shrter wavelengths, the region of focus is, essentially, defined by the wavelength. I.e. at say 1 kHz, you are simply NOT going to have any precision in focusing smaller than a couple of feet at best. |
#32
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On Dec 25, 3:25 pm, Uncle Al wrote:
Whispering galleries and inside elliptic reflectors, yes. This is the preferred way to build confessionals in church - at one focus - with rentable scholarship rooms at the other focus. Really? I"m going to have to look into this. I"m thinking I'd really like to line up a few "scholarship" hours at peak confession times! Parabolic reflector (satellite dish), not so much. Incoming will be focused but outgoing will be collimated. Obviously the "whispering gallery" setup would use TWO parabolic reflectors which is the equivalent of the elliptic chamber. Both are conic sections and work nearly the same. A single parabolic reflector is the usual microphone setup. But a single reflector is the "I see you, you see me" equivalent of only ONE person with a telescope as opposed to each person having one. If both persons have similar telescopes then that is the optical equivalent of a "whispering chamber". And I might mention that acoustic lenses exist as well so a reflector isn't essential to create the effects. |
#33
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#34
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acoustics
On Dec 29, 10:11 am, "Ethan Winer" ethanw at ethanwiner dot com
wrote: wrote: ... snip ... Interesting stuff. So with only one dish, is "I see you, you see me" true? Well, look at the optical analogy: with piece of equipment available for under $5,000, you can see details on the moon with a resolution on the order of a kilometer or less. But the person standing on the moon without such an optical aid couldn't even begin to resolve the county you live in. It's a somewhat extreme example of the general case, but going back to the acoustic equivalent, there is gain going in both directions, but it is not entirely symmetrical. Assume both "transmitters (i.e., persons speaking) radiate omni- directionally. In the case of the speaker and no reflector, the entire energy is emitted in all directions, and a far away reflector intercepts only a very small portion of the radiated power. However, the speaker is placed at the principle focal point of the reflector, the reflector intercepts a much larger portion of the total radiated power and collimates it into a beam. Imagine, for instance, a 1 meter diameter reflector and the receiver and transmitter placed 30 meters apart. In the former case, the reflector at the receiving end intercepts only about 0.11% of the total radiated acoustic power of the transmitter, whereas in the latter case, where the focal length might be on the order of a half meter, it intercepts maybe 30% of the energy. However, the use of the reflector at the transmitter does not, as assumed in the discussion, result in a collimated beam with no divergence, for the reasons mentioned previously. Rather, it, too, has divergence which is wave- length and thus frequency dependent: more divergence at lower frequencies than at high. Be all that as it may, the result is more along the lines of "I hear you a bit better than you hear me., or maybe not, depends." :-) |
#35
Posted to sci.physics,sci.electronics.basics,rec.audio.tech
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acoustics
Be all that as it may, the result is more along the lines of
"I hear you a bit better than you hear me., or maybe not, depends." :-) Thanks. |
#36
Posted to sci.physics, sci.electronics.basics, rec.audio.tech
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acoustics
On Dec 27 2007, 2:52*pm, (Bob Masta) wrote:
On Wed, 26 Dec 2007 09:01:06 -0500, "Ethan Winer" ethanw at ethanwiner dot com wrote: Bob, The output is not "focused" in the same sense as when the dish is used as a collector Yes, but the person away from the collector isn't a "large" source either.. So it still seems it would be 100 percent reciprocal, no? This is like half of a pair of reflectors like you see in parks, where two people can be hundreds of yards away and talk as if they're next to each other. You have given the answer in your example: *If one reflector was all it took to get 100% reciprocal operation, then they wouldn't use two reflectors. Suppose we think of this with light beams instead of sound waves, and use laser pointers so that we have a planar wave front. * The guy without a reflector can aim his beam at the distant reflector, which might have an area of (say) 10 square feet, and anywhere he aims within that area the beam will be captured and received more-or-less 100% at the focal point. But the guy at the focal point can't do the same thing in reverse. *He either needs to aim his beam *exactly* at the other guy (avoiding the reflector, or bouncing it on a careful trajectory), or else he needs many, many beams at slightly different trajectories so that they will cover the same 10 square-foot area at full intensity at the reflectorless guy's end. * Best regards, Bob Masta * * * * * * * DAQARTA *v3.50 * *Data AcQuisition And Real-Time Analysis * * * * * * *www.daqarta.com Scope, Spectrum, Spectrogram, FREE Signal Generator * * * * Science with your sound card! In that connection seems a procedure interesting, restores acoustic wave fronts according huygens principle: http:www.syntheticwave.de H. |
#37
Posted to sci.physics, sci.electronics.basics, rec.audio.tech
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acoustics
On Jan 16, 12:37 am, syntheticwave wrote:
In that connection seems a procedure interesting, restores acoustic wave fronts according huygens principle: http:www.syntheticwave.de ... possibly does not become clear from the link above alone, why connected that animation with the topic "see I you, you see me" discussed here. Therefore I would like to justify, what I want to express by the link: We must include the Huygens principle ( http://en.wikipedia.org/wiki/Huygens_principle ) into the view of the topic. Thus acoustic waves can be bundled or diverged or nearly at will aligned by the represented loudspeaker field. Just suitably delay for each elementary wave would be need. Perhaps that becomes clearer with the "acoustic curtain" animation: http://www.syntheticwave.de/acoustic%20curtain.htm With the light waves the conditions are alike in principle yet, but both propagation speed and wavelength are by completely different dimensions. If the light is not coherent, it hardly comes to extinctions and overlays, as with the many longer acoustic waves the case is. Therefore applies see I you, you normally sees me. But whether I hear you, it depends on the fact how the elementary waves superimpose. Greetings Helmut, and sorry for my bad English ļ |
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