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#1
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Hi, I've been chasing high dollar speaker cables for years. Finally, I
decided to make one myself. However, I don't know how to measure the spec. of the cable. Like how to use a handheld LCR meter to measure one speaker cable's inductance and/or capacitance? Could anyone kind enough to help me? Thanks in advance! Lawrence Leung |
#2
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Lawrence:
Find out the frequency that the LCR meter uses to measure with. Use a piece of cable -much- shorter than a wavelength of this frequency. Measure the capacitance of an open circuited piece Measure the inductance of a short circuted piece. divide by the length of the piece to get cap per unit length and inductance per unit length. characteristic impedance is sqrt(l/c) propagation constant is sqrt(l*c) -------------------------------- More accurate measurements can be made taking into account the actual length of the piece of cable. Regards, Cliff "Lawrence Leung" wrote in message 54... Hi, I've been chasing high dollar speaker cables for years. Finally, I decided to make one myself. However, I don't know how to measure the spec. of the cable. Like how to use a handheld LCR meter to measure one speaker cable's inductance and/or capacitance? Could anyone kind enough to help me? Thanks in advance! Lawrence Leung |
#3
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Lawrence:
Find out the frequency that the LCR meter uses to measure with. Use a piece of cable -much- shorter than a wavelength of this frequency. Measure the capacitance of an open circuited piece Measure the inductance of a short circuted piece. divide by the length of the piece to get cap per unit length and inductance per unit length. characteristic impedance is sqrt(l/c) propagation constant is sqrt(l*c) -------------------------------- More accurate measurements can be made taking into account the actual length of the piece of cable. Regards, Cliff "Lawrence Leung" wrote in message 54... Hi, I've been chasing high dollar speaker cables for years. Finally, I decided to make one myself. However, I don't know how to measure the spec. of the cable. Like how to use a handheld LCR meter to measure one speaker cable's inductance and/or capacitance? Could anyone kind enough to help me? Thanks in advance! Lawrence Leung |
#4
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In article S7Gpb.99545$HS4.838304@attbi_s01,
"Cliff Curry" wrote: Lawrence: Find out the frequency that the LCR meter uses to measure with. Use a piece of cable -much- shorter than a wavelength of this frequency. Measure the capacitance of an open circuited piece Measure the inductance of a short circuted piece. divide by the length of the piece to get cap per unit length and inductance per unit length. Note: characteristic impedance is sqrt(l/c) propagation constant is sqrt(l*c) Those approximations are not in general true below a few hundred kilohertz or so. In the audio range, there is no "characteristic impedance"; instead, at each frequency there is an impedance for *that frequency only*. The same goes for propagation, which is frequency-dependent. The way those parameters vary with frequency is critically dependent upon the physical construction of the line. For example, as frequency drops without limit, the propagation velocity also drops *without limit*. Find out why early long-distance telephone lines needed "loading coils". Then find out why they all were removed. See the wonderful Schaum's Outline book on Transmission Lines for more information on this. More accurate measurements can be made taking into account the actual length of the piece of cable. Better still is to avoid the need for measurements at all. Theoretical calculations will get you fairly close, for cables of any length useful for speakers -- under a hundred feet, say; do it for a few different sets of materials and different constructions if you like. Learning enough to understand whether values anywhere near the ones you calculated could have any possible effect on audible frequencies being supplied by a decent, real-world amplifier to any rational set of speakers will get you the rest of the way to true enlightenment. Isaac |
#5
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In article S7Gpb.99545$HS4.838304@attbi_s01,
"Cliff Curry" wrote: Lawrence: Find out the frequency that the LCR meter uses to measure with. Use a piece of cable -much- shorter than a wavelength of this frequency. Measure the capacitance of an open circuited piece Measure the inductance of a short circuted piece. divide by the length of the piece to get cap per unit length and inductance per unit length. Note: characteristic impedance is sqrt(l/c) propagation constant is sqrt(l*c) Those approximations are not in general true below a few hundred kilohertz or so. In the audio range, there is no "characteristic impedance"; instead, at each frequency there is an impedance for *that frequency only*. The same goes for propagation, which is frequency-dependent. The way those parameters vary with frequency is critically dependent upon the physical construction of the line. For example, as frequency drops without limit, the propagation velocity also drops *without limit*. Find out why early long-distance telephone lines needed "loading coils". Then find out why they all were removed. See the wonderful Schaum's Outline book on Transmission Lines for more information on this. More accurate measurements can be made taking into account the actual length of the piece of cable. Better still is to avoid the need for measurements at all. Theoretical calculations will get you fairly close, for cables of any length useful for speakers -- under a hundred feet, say; do it for a few different sets of materials and different constructions if you like. Learning enough to understand whether values anywhere near the ones you calculated could have any possible effect on audible frequencies being supplied by a decent, real-world amplifier to any rational set of speakers will get you the rest of the way to true enlightenment. Isaac |
#6
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Isaac Wingfield wrote in message ...
In article S7Gpb.99545$HS4.838304@attbi_s01, "Cliff Curry" wrote: Note: characteristic impedance is sqrt(l/c) propagation constant is sqrt(l*c) Those approximations are not in general true below a few hundred kilohertz or so. In the audio range, there is no "characteristic impedance"; instead, at each frequency there is an impedance for *that frequency only*. It is true there is no "characteristic impedance" for long coax cables, at frequencies below several hundred KHz. However, Zo = sqrt(L/C), will hold for *any* frequency if: R = 0 and G = 0. (R the resistance of the cable and, G the conductance). In the case of heavy gage (12 gage) audio cables , of a short length (25 ft), R and G are very close to zero. For this case, the calculated characterisitc impedance will hold down to audio frequenies. Bob Stanton |
#7
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Isaac Wingfield wrote in message ...
In article S7Gpb.99545$HS4.838304@attbi_s01, "Cliff Curry" wrote: Note: characteristic impedance is sqrt(l/c) propagation constant is sqrt(l*c) Those approximations are not in general true below a few hundred kilohertz or so. In the audio range, there is no "characteristic impedance"; instead, at each frequency there is an impedance for *that frequency only*. It is true there is no "characteristic impedance" for long coax cables, at frequencies below several hundred KHz. However, Zo = sqrt(L/C), will hold for *any* frequency if: R = 0 and G = 0. (R the resistance of the cable and, G the conductance). In the case of heavy gage (12 gage) audio cables , of a short length (25 ft), R and G are very close to zero. For this case, the calculated characterisitc impedance will hold down to audio frequenies. Bob Stanton |
#8
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#9
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#10
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![]() "Lawrence Leung" wrote ... Hi, I've been chasing high dollar speaker cables for years. Finally, I decided to make one myself. What on earth for? Speaker cables are one of the most hyped subjects in the entire audio world - as long as it's decent thick copper wire, doesn't go open or short circuit, and has enough cores to carry the signal, anything will do! At a recent audio trade fair, a *very* reputable UK speaker manufacturer was demonstating a new pair of speakers - all the "golden-eared" HiFi reviewers were raving about the wonderful "clarity and transparency of the treble, the fluid bass" (and rightly so). An unpretentious reporter noticed some familiar-looking orange cable running across the room, behind the wall drapes - "is that what it looks like?" he asked; "yeah, we forgot to bring the cables, so I popped over the road to Homebase and picked up one of their Black&Decker garden extension cables - they're good thick copper, make great speaker cables" Personally, I use QED 79-strand well terminated in sturdy connectors - it's about as far as I want to go into expensive cables - and pay more attention to obstructions and reflective surfaces in front of the speakers, which make a hell of a lot more difference! YMMV, Dave H. (The engineer formerly known as Homeless) (ex senior engineer at a reputable pro-audio manufacturer, etc.) |
#11
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![]() "Lawrence Leung" wrote ... Hi, I've been chasing high dollar speaker cables for years. Finally, I decided to make one myself. What on earth for? Speaker cables are one of the most hyped subjects in the entire audio world - as long as it's decent thick copper wire, doesn't go open or short circuit, and has enough cores to carry the signal, anything will do! At a recent audio trade fair, a *very* reputable UK speaker manufacturer was demonstating a new pair of speakers - all the "golden-eared" HiFi reviewers were raving about the wonderful "clarity and transparency of the treble, the fluid bass" (and rightly so). An unpretentious reporter noticed some familiar-looking orange cable running across the room, behind the wall drapes - "is that what it looks like?" he asked; "yeah, we forgot to bring the cables, so I popped over the road to Homebase and picked up one of their Black&Decker garden extension cables - they're good thick copper, make great speaker cables" Personally, I use QED 79-strand well terminated in sturdy connectors - it's about as far as I want to go into expensive cables - and pay more attention to obstructions and reflective surfaces in front of the speakers, which make a hell of a lot more difference! YMMV, Dave H. (The engineer formerly known as Homeless) (ex senior engineer at a reputable pro-audio manufacturer, etc.) |
#12
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#13
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#14
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![]() "Bob-Stanton" wrote in message om... Isaac Wingfield wrote in message ... snip The point I think we are both making is that if the line is short enough (in terms of the wavelengths it is carrying), then the line has no particular characteristics (resistance aside) that could affect the signal. That is certainly the case for domestic speaker cables. Isaac You're right, I agree. Bob Stanton Aw, c'mon Bob - this is the net, you're not allowed to say that, and even with the devil apostrophe in the right place! Regards Ian ;-) |
#15
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![]() "Bob-Stanton" wrote in message om... Isaac Wingfield wrote in message ... snip The point I think we are both making is that if the line is short enough (in terms of the wavelengths it is carrying), then the line has no particular characteristics (resistance aside) that could affect the signal. That is certainly the case for domestic speaker cables. Isaac You're right, I agree. Bob Stanton Aw, c'mon Bob - this is the net, you're not allowed to say that, and even with the devil apostrophe in the right place! Regards Ian ;-) |
#16
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"Dave H." wrote in
: "Lawrence Leung" wrote ... Hi, I've been chasing high dollar speaker cables for years. Finally, I decided to make one myself. What on earth for? Speaker cables are one of the most hyped subjects in the entire audio world - as long as it's decent thick copper wire, doesn't go open or short circuit, and has enough cores to carry the signal, anything will do! At a recent audio trade fair, a *very* reputable UK speaker manufacturer was demonstating a new pair of speakers - all the "golden-eared" HiFi reviewers were raving about the wonderful "clarity and transparency of the treble, the fluid bass" (and rightly so). An unpretentious reporter noticed some familiar-looking orange cable running across the room, behind the wall drapes - "is that what it looks like?" he asked; "yeah, we forgot to bring the cables, so I popped over the road to Homebase and picked up one of their Black&Decker garden extension cables - they're good thick copper, make great speaker cables" Personally, I use QED 79-strand well terminated in sturdy connectors - it's about as far as I want to go into expensive cables - and pay more attention to obstructions and reflective surfaces in front of the speakers, which make a hell of a lot more difference! YMMV, Dave H. (The engineer formerly known as Homeless) (ex senior engineer at a reputable pro-audio manufacturer, etc.) First of all, thank you so much for all the fellows for your inputs. Well, I have to admit that, high dollar speaker cables really make the difference, but the point is, rather the difference(s) worth the high dollar. I listened to a USD$0.30/ft cable and a USD$150.00/ft cable, they sound REALLY difference, the high dollar cable REALLY sounds better, but defintely not 500 times better than then cheap cable!!! ![]() That is one of the reasons that I try to make speaker cable myself, I just make one with double 12 AWG "normal" speaker cable (USD$0.40/ft), terminated it real good, heat shrink it, put on foil, nylon sleeving the whole nine yards, and guess what? I spent about USD$50.00 for that pair of speaker cables and it sounds almost as good as my Analysis-Plus Oval 9 (which is about USD$500.00), although my cable lack a little bit detail in the mid-range, the high pitch is not as clear. But, I blame it as new cables, need another 100 hours to break-in. What I want is to find out the characteristic of the Oval 9, like the Q, L, and C. Then compare them with my home-made cable's Q, L, and C to see if the "difference" can be quantified!!! Hey, if I told you I make a good living, you might not have any idea what "good living" mean, but if I told you I make 3 million dollars salary per year, then you know what my good living mean! We all live in a "number" world! Once again, thanks for all the inputs, please keep feed me with information and knowledge. Lawrence Leung |
#17
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"Dave H." wrote in
: "Lawrence Leung" wrote ... Hi, I've been chasing high dollar speaker cables for years. Finally, I decided to make one myself. What on earth for? Speaker cables are one of the most hyped subjects in the entire audio world - as long as it's decent thick copper wire, doesn't go open or short circuit, and has enough cores to carry the signal, anything will do! At a recent audio trade fair, a *very* reputable UK speaker manufacturer was demonstating a new pair of speakers - all the "golden-eared" HiFi reviewers were raving about the wonderful "clarity and transparency of the treble, the fluid bass" (and rightly so). An unpretentious reporter noticed some familiar-looking orange cable running across the room, behind the wall drapes - "is that what it looks like?" he asked; "yeah, we forgot to bring the cables, so I popped over the road to Homebase and picked up one of their Black&Decker garden extension cables - they're good thick copper, make great speaker cables" Personally, I use QED 79-strand well terminated in sturdy connectors - it's about as far as I want to go into expensive cables - and pay more attention to obstructions and reflective surfaces in front of the speakers, which make a hell of a lot more difference! YMMV, Dave H. (The engineer formerly known as Homeless) (ex senior engineer at a reputable pro-audio manufacturer, etc.) First of all, thank you so much for all the fellows for your inputs. Well, I have to admit that, high dollar speaker cables really make the difference, but the point is, rather the difference(s) worth the high dollar. I listened to a USD$0.30/ft cable and a USD$150.00/ft cable, they sound REALLY difference, the high dollar cable REALLY sounds better, but defintely not 500 times better than then cheap cable!!! ![]() That is one of the reasons that I try to make speaker cable myself, I just make one with double 12 AWG "normal" speaker cable (USD$0.40/ft), terminated it real good, heat shrink it, put on foil, nylon sleeving the whole nine yards, and guess what? I spent about USD$50.00 for that pair of speaker cables and it sounds almost as good as my Analysis-Plus Oval 9 (which is about USD$500.00), although my cable lack a little bit detail in the mid-range, the high pitch is not as clear. But, I blame it as new cables, need another 100 hours to break-in. What I want is to find out the characteristic of the Oval 9, like the Q, L, and C. Then compare them with my home-made cable's Q, L, and C to see if the "difference" can be quantified!!! Hey, if I told you I make a good living, you might not have any idea what "good living" mean, but if I told you I make 3 million dollars salary per year, then you know what my good living mean! We all live in a "number" world! Once again, thanks for all the inputs, please keep feed me with information and knowledge. Lawrence Leung |
#18
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On Thu, 06 Nov 2003 23:34:15 GMT, Lawrence Leung
wrote: Well, I have to admit that, high dollar speaker cables really make the difference, but the point is, rather the difference(s) worth the high dollar. I listened to a USD$0.30/ft cable and a USD$150.00/ft cable, they sound REALLY difference, the high dollar cable REALLY sounds better, but defintely not 500 times better than then cheap cable!!! ![]() Try listening to them again, when you don't *know* which cable is connected. You'll find that all these 'REAL' differences vanish...... -- Stewart Pinkerton | Music is Art - Audio is Engineering |
#19
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On Thu, 06 Nov 2003 23:34:15 GMT, Lawrence Leung
wrote: Well, I have to admit that, high dollar speaker cables really make the difference, but the point is, rather the difference(s) worth the high dollar. I listened to a USD$0.30/ft cable and a USD$150.00/ft cable, they sound REALLY difference, the high dollar cable REALLY sounds better, but defintely not 500 times better than then cheap cable!!! ![]() Try listening to them again, when you don't *know* which cable is connected. You'll find that all these 'REAL' differences vanish...... -- Stewart Pinkerton | Music is Art - Audio is Engineering |
#21
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In , on 11/07/03
at 08:01 AM, (Stewart Pinkerton) said: [ ... ] Try listening to them again, when you don't *know* which cable is connected. You'll find that all these 'REAL' differences vanish...... About half of the "magic" of tricky cables occurrs when you break down the original connection (thus scraping off some of the oxides and crud) and connect the new, wonderful cables. I recommend that everyone break down their system once or twice a year and reconnect everything. If you hear a difference after this exercise, increase the frequency of these breakdowns. ----------------------------------------------------------- SPAM: wordgame:123(abc):14 9 20 5 2 9 18 4 at 22 15 9 3 5 14 5 20 dot 3 15 13 (Barry Mann) [sorry about the puzzle, SPAMers are ruining my mailbox] ----------------------------------------------------------- |
#22
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"Lawrence Leung" wrote in message
54 First of all, thank you so much for all the fellows for your inputs. The best thanks is credibility. Well, I have to admit that, high dollar speaker cables really make the difference, but the point is, rather the difference(s) worth the high dollar. Not at all. I listened to a USD$0.30/ft cable and a USD$150.00/ft cable, they sound REALLY difference, the high dollar cable REALLY sounds better, but defintely not 500 times better than then cheap cable!!! ![]() I seriously doubt that you just listened when you made this comparison. Typically comparisons like this are made under the worst of circumstances from the standpoint of just listening. The levels aren't matched, the listening opportunities aren't time-synched, and there are no bias controls. Indeed the alleged listening test may be contemporaneous with a sales pitch for the more expensive cable. That is one of the reasons that I try to make speaker cable myself, I just make one with double 12 AWG "normal" speaker cable (USD$0.40/ft), terminated it real good, heat shrink it, put on foil, nylon sleeving the whole nine yards, and guess what? I spent about USD$50.00 for that pair of speaker cables and it sounds almost as good as my Analysis-Plus Oval 9 (which is about USD$500.00), although my cable lack a little bit detail in the mid-range, the high pitch is not as clear. But, I blame it as new cables, need another 100 hours to break-in. Cable break-in is another one of those areas where much so-called evidence is not obtained by means of just listening. What I want is to find out the characteristic of the Oval 9, like the Q, L, and C. Then compare them with my home-made cable's Q, L, and C to see if the "difference" can be quantified!!! Been there, done that. Slightly different context, but... Hey, if I told you I make a good living, you might not have any idea what "good living" mean, but if I told you I make 3 million dollars salary per year, then you know what my good living mean! Then you understand the pitfalls of unrestrained subjectivity. We all live in a "number" world! Not only a number world, but also a world where some numbers represent differences that are irrelevant to human experience. Once again, thanks for all the inputs, please keep feed me with information and knowledge. First off, learn how to "just listen". Free, online interactive tutorials on that subject can be found at www.pcabx.com . |
#23
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"Lawrence Leung" wrote in message
54 First of all, thank you so much for all the fellows for your inputs. The best thanks is credibility. Well, I have to admit that, high dollar speaker cables really make the difference, but the point is, rather the difference(s) worth the high dollar. Not at all. I listened to a USD$0.30/ft cable and a USD$150.00/ft cable, they sound REALLY difference, the high dollar cable REALLY sounds better, but defintely not 500 times better than then cheap cable!!! ![]() I seriously doubt that you just listened when you made this comparison. Typically comparisons like this are made under the worst of circumstances from the standpoint of just listening. The levels aren't matched, the listening opportunities aren't time-synched, and there are no bias controls. Indeed the alleged listening test may be contemporaneous with a sales pitch for the more expensive cable. That is one of the reasons that I try to make speaker cable myself, I just make one with double 12 AWG "normal" speaker cable (USD$0.40/ft), terminated it real good, heat shrink it, put on foil, nylon sleeving the whole nine yards, and guess what? I spent about USD$50.00 for that pair of speaker cables and it sounds almost as good as my Analysis-Plus Oval 9 (which is about USD$500.00), although my cable lack a little bit detail in the mid-range, the high pitch is not as clear. But, I blame it as new cables, need another 100 hours to break-in. Cable break-in is another one of those areas where much so-called evidence is not obtained by means of just listening. What I want is to find out the characteristic of the Oval 9, like the Q, L, and C. Then compare them with my home-made cable's Q, L, and C to see if the "difference" can be quantified!!! Been there, done that. Slightly different context, but... Hey, if I told you I make a good living, you might not have any idea what "good living" mean, but if I told you I make 3 million dollars salary per year, then you know what my good living mean! Then you understand the pitfalls of unrestrained subjectivity. We all live in a "number" world! Not only a number world, but also a world where some numbers represent differences that are irrelevant to human experience. Once again, thanks for all the inputs, please keep feed me with information and knowledge. First off, learn how to "just listen". Free, online interactive tutorials on that subject can be found at www.pcabx.com . |
#24
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![]() Isaac Wingfield wrote in message ... snip The point I think we are both making is that if the line is short enough (in terms of the wavelengths it is carrying), then the line has no particular characteristics (resistance aside) that could affect the signal. That is certainly the case for domestic speaker cables. Isaac I'm not sure I agree with that. Speaker cables are all short relative to the wavelengths being carried. For your statement to be true, there would never be a reason to be concerned with inductance, and we all know that's not true. Norm Strong |
#25
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![]() Isaac Wingfield wrote in message ... snip The point I think we are both making is that if the line is short enough (in terms of the wavelengths it is carrying), then the line has no particular characteristics (resistance aside) that could affect the signal. That is certainly the case for domestic speaker cables. Isaac I'm not sure I agree with that. Speaker cables are all short relative to the wavelengths being carried. For your statement to be true, there would never be a reason to be concerned with inductance, and we all know that's not true. Norm Strong |
#26
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"normanstrong" wrote in message news:9rRqb.101076
I'm not sure I agree with that. Speaker cables are all short relative to the wavelengths being carried. For your statement to be true, there would never be a reason to be concerned with inductance, and we all know that's not true. How a speaker cable behaves, whether as a transmission line or as a discrete device, is determined by the *resistance* of the conductors, not by it's wavelength at audio frequencies. If a transmission line was supercooled, and had zero resistance, it would act as a "high frequency" transmission line at *all* frequencies. Unfortunatly, the speaker cables ( 12 gage) in my house are at room temperature, and they don't act like "high frequency" transmission lines at *all* audio frequencies. At 20KHz they act mostly (sort of) like "high frequency" transmission lines, at 200 Hz they act like discrete components. The region beween 200 Hz and 20KHz is called the transition region. In the transition region, lines sort of act like "high frequency" transmission lines, and sort of act like discrete components. This makes life very difficult. :-) At 20 KHz, you can't really treet a speaker cable as a discrete inductor. A 100 ft length of 12 gage, speaker cable would have 20uH of inductance. If you calculate the loss as a simple series L, R, you would get a 0.62 dB loss (with an 8 Ohm load). If you calculate the speaker cable as a transmission line, (which it mostly is at 20 KHz) you get 0.32 dB loss. Which one is right. Dammed if I know. ;-) Bob Stanton |
#27
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"normanstrong" wrote in message news:9rRqb.101076
I'm not sure I agree with that. Speaker cables are all short relative to the wavelengths being carried. For your statement to be true, there would never be a reason to be concerned with inductance, and we all know that's not true. How a speaker cable behaves, whether as a transmission line or as a discrete device, is determined by the *resistance* of the conductors, not by it's wavelength at audio frequencies. If a transmission line was supercooled, and had zero resistance, it would act as a "high frequency" transmission line at *all* frequencies. Unfortunatly, the speaker cables ( 12 gage) in my house are at room temperature, and they don't act like "high frequency" transmission lines at *all* audio frequencies. At 20KHz they act mostly (sort of) like "high frequency" transmission lines, at 200 Hz they act like discrete components. The region beween 200 Hz and 20KHz is called the transition region. In the transition region, lines sort of act like "high frequency" transmission lines, and sort of act like discrete components. This makes life very difficult. :-) At 20 KHz, you can't really treet a speaker cable as a discrete inductor. A 100 ft length of 12 gage, speaker cable would have 20uH of inductance. If you calculate the loss as a simple series L, R, you would get a 0.62 dB loss (with an 8 Ohm load). If you calculate the speaker cable as a transmission line, (which it mostly is at 20 KHz) you get 0.32 dB loss. Which one is right. Dammed if I know. ;-) Bob Stanton |
#28
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#29
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#30
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(Per Stromgren) wrote in message ...
On 9 Nov 2003 03:48:40 -0800, (Bob-Stanton) wrote: "normanstrong" wrote in message news:9rRqb.101076 I'm not sure I agree with that. Speaker cables are all short relative to the wavelengths being carried. For your statement to be true, there would never be a reason to be concerned with inductance, and we all know that's not true. At 20KHz they act mostly (sort of) like "high frequency" transmission lines, at 200 Hz they act like discrete components. At 20 kHz, the wavelength at speed of light is 3*E8/20*E3=1.5*E4m, i.e. 15 km or about 9 miles. Your 100 ft of cable is 2/1000th of that, hardly a transmission line, even if we take into consideration a somewhat slower speed in the cable. Or do you say that it still will act as a transmission line? It is not, according to the books I own. Are you familiar with the Smith Chart? It is probably the most usesful graphical tool available to the RF designer. It was originally conceived by Phil Smith, in Bell Labs, in the 1930's and it is still widely in use. One of the Smith Chart's uses is to calculate the impedance change of a transmission line. The Smith Chart is a circular graph that is divided into wavelenths (and degrees). One full rotation around the chart equals one wavelength. 1 deg rotation equals 0.0028 WL of a transmission line. The Smith chart is readable down to about 1/2 degree, which equals 0.0014 wavelength. The chart will accurately show the change of impedance along a transmission line that is only 0.002 wavelengths long. I used an RF computer program to calculate the impedance(and loss) of 100 ft (of 100 Ohm) speaker cable terminated with an 8 Ohm load. Then, I checked the calculations by hand, using a Smith Chart. The Smith Chart results agreed with the computer program. They both showed that fractional wavelengh transmission lines "work". If you feel that fractional wavelengh transmission lines don't "work", you should throw away your Smith Chart, or perhaps just whiteout the fractional wavelength part of the Smith Chart, that you don't agree with. :-) As for me, I'll keep my old Smith Chart, because it shows that fractional wavelength transmission lines do "work" and it can calculate how they work. Bob Stanton |
#31
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(Per Stromgren) wrote in message ...
On 9 Nov 2003 03:48:40 -0800, (Bob-Stanton) wrote: "normanstrong" wrote in message news:9rRqb.101076 I'm not sure I agree with that. Speaker cables are all short relative to the wavelengths being carried. For your statement to be true, there would never be a reason to be concerned with inductance, and we all know that's not true. At 20KHz they act mostly (sort of) like "high frequency" transmission lines, at 200 Hz they act like discrete components. At 20 kHz, the wavelength at speed of light is 3*E8/20*E3=1.5*E4m, i.e. 15 km or about 9 miles. Your 100 ft of cable is 2/1000th of that, hardly a transmission line, even if we take into consideration a somewhat slower speed in the cable. Or do you say that it still will act as a transmission line? It is not, according to the books I own. Are you familiar with the Smith Chart? It is probably the most usesful graphical tool available to the RF designer. It was originally conceived by Phil Smith, in Bell Labs, in the 1930's and it is still widely in use. One of the Smith Chart's uses is to calculate the impedance change of a transmission line. The Smith Chart is a circular graph that is divided into wavelenths (and degrees). One full rotation around the chart equals one wavelength. 1 deg rotation equals 0.0028 WL of a transmission line. The Smith chart is readable down to about 1/2 degree, which equals 0.0014 wavelength. The chart will accurately show the change of impedance along a transmission line that is only 0.002 wavelengths long. I used an RF computer program to calculate the impedance(and loss) of 100 ft (of 100 Ohm) speaker cable terminated with an 8 Ohm load. Then, I checked the calculations by hand, using a Smith Chart. The Smith Chart results agreed with the computer program. They both showed that fractional wavelengh transmission lines "work". If you feel that fractional wavelengh transmission lines don't "work", you should throw away your Smith Chart, or perhaps just whiteout the fractional wavelength part of the Smith Chart, that you don't agree with. :-) As for me, I'll keep my old Smith Chart, because it shows that fractional wavelength transmission lines do "work" and it can calculate how they work. Bob Stanton |
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On Mon, 10 Nov 2003 09:24:47 +0100, Per Stromgren
wrote: No, I was not aware of the Smith chart, I'm afraid. But it seems to me (after some 30 minutes of Googling I just performed) that it is just a calculation tool, and it does not per se introduce any alternative theory. As far as I can see, there is no mention of this tool to work in the application you just showed us. Most sources say "RF broadband use only" or something to that effect. "RF ***narrowband*** use only", of course. Sorry about that. Per. |
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On Mon, 10 Nov 2003 09:24:47 +0100, Per Stromgren
wrote: No, I was not aware of the Smith chart, I'm afraid. But it seems to me (after some 30 minutes of Googling I just performed) that it is just a calculation tool, and it does not per se introduce any alternative theory. As far as I can see, there is no mention of this tool to work in the application you just showed us. Most sources say "RF broadband use only" or something to that effect. "RF ***narrowband*** use only", of course. Sorry about that. Per. |
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Per Stromgren wrote in message
line. No, I was not aware of the Smith chart, I'm afraid. But it seems to me (after some 30 minutes of Googling I just performed) that it is just a calculation tool, and it does not per se introduce any alternative theory. As far as I can see, there is no mention of this tool to work in the application you just showed us. Most sources say "RF broadband use only" or something to that effect. Or did I miss something? Per. A Smith will show the change of impedance of a transmission line, for a line as short as 0.002 WL. This is not a new theory, it's just the way it is. If one rotates the cursor of a Smith chart by 0.002 WL, one will be able to read, how the impedance of a 0.002 WL line changes. There is no low frequency limit to Smith Charts. The only limits a the transmission line must be at least 0.002 WL long and the line must have very low series resistance. The case I cited was a 100 ft line, of 12 gage wire. A line of 100 Ft is just barely long enough to allow Smith chart calculations. A 12 gage cable has just barely low enough series resistance, to allow the Smith chart to work accurately. Of one thing I'm su calculating the loss of a 100 ft line, using discrete component models, will not give correct results. Bob Stanton |
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