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Speaker wire - another fine theory
"René" wrote in message
news:dJo5b.342490$o%2.157128@sccrnsc02... Please allow me to introduce (yet) another mechanism of distortion: Speaker wires can carry substantial AC currents, which in turn generate measurable magnetic fields. As the "+" and "-" wires are usually positioned side by side, some mechanical forces are working on them. The plastic (?) isolator material is somewhat elastic, therefor allowing a minimum of relative movement. This effect is not trivial - with a shorted length of cable and a DC current of a few 10's of amps - the motion can actually be felt! With speakers dipping to one ohm i.e. Apogees driven by the larger Krells surely this would already have been an area of concern? This in turn allows the wires to move respective to one another, and by doing so, dissipate a measure of energy. This obviously leads to a degree of distortion of the signal arriving at the speaker. To come to the point: I do not worry at all about the above effect. If as you surmise this leads to a degree of distortion then you should be worried if this is in fact the case. Still I would suspect that this effect is notably stronger (and perhaps even *measurable*!) than esoteric effects relating to HI-end mains cable, or "played-in" interlinks with designated in and outputs. It amazes me that this rather obvious effect seems not be discussed in hi -end circles. (or is it?) A *true* High ender is henceforth expected to use loudspeaker wiring with spreaders that keeps the conductors well apart lest he will not be taken seriously. Cogan-Hall loudspeaker cable construction was of parallel copper tube conductors with spreaders approx. every three inches. To come to the final point (finally): why are very subtle mechanisms of distortion so magnified in the various discussions - and an obvious mechanism like described above is scarcely heard off? Because this is a High End news group where subtle distortions are hopefully considered important. I'm sure some cable manufacturer somewhere has already described this effect in verbose prose already. Wow its too big to ignore - cables actually moving! Disclaimer: if somebody makes money out of this idea - I like to have a fair sha-) Ok do some serious testing then market a speaker cable that is 'motion' free (take that in its literal sense) then laugh all the way to the bank ;-) Mike -- - René |
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Speaker wire - another fine theory
In article dJo5b.342490$o%2.157128@sccrnsc02, René wrote:
Please allow me to introduce (yet) another mechanism of distortion: Speaker wires can carry substantial AC currents, which in turn generate measurable magnetic fields. As the "+" and "-" wires are usually positioned side by side, some mechanical forces are working on them. The plastic (?) isolator material is somewhat elastic, therefor allowing a minimum of relative movement. This effect is not trivial - with a shorted length of cable and a DC current of a few 10's of amps - the motion can actually be felt! This in turn allows the wires to move respective to one another, and by doing so, dissipate a measure of energy. This obviously leads to a degree of distortion of the signal arriving at the speaker. Why do you think such a phenomenon would lead to distortion? If it's dissipating energy, then it will simply increase the electrical losses in the cable, though by an EXTRAORDINALLY insiginifcant amount. This is equivalent to adding a TINY amount of electrical resistance to the cable. Still I would suspect that this effect is notably stronger (and perhaps even *measurable*!) than esoteric effects relating to HI-end mains cable, or "played-in" interlinks with designated in and outputs. It amazes me that this rather obvious effect seems not be discussed in hi -end circles. (or is it?) Becasue it is NOT "rather obvious." It's extremely tiny and wholly insignificant AND if your claim is correct, it's a simple linear inscrease in resistance. A *true* High ender is henceforth expected to use loudspeaker wiring with spreaders that keeps the conductors well apart lest he will not be taken seriously. A "high ender" that worried about such an effect would be asking not to be taken seriously. Simply constraining the cables so they don't move relative to one another, like most speaker cables are made, is enough to essentially remder any such effect irrelevant. SPreading the cables apart has the effect of ncreasing the inductance of the cable. To come to the final point (finally): why are very subtle mechanisms of distortion so magnified in the various discussions - and an obvious mechanism like described above is scarcely heard off? Because it's not fistorion, it's loss. If you think that's a problem, simply go one or two gauges heavire in wire, and that will TOTALLY swamp out ANY such effects. -- | Dick Pierce | | Professional Audio Development | | 1-781/826-4953 Voice and FAX | | | |
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Speaker wire - another fine theory
On Wed, 03 Sep 2003 16:33:13 GMT, René wrote:
Please allow me to introduce (yet) another mechanism of distortion: Speaker wires can carry substantial AC currents, which in turn generate measurable magnetic fields. As the "+" and "-" wires are usually positioned side by side, some mechanical forces are working on them. The plastic (?) isolator material is somewhat elastic, therefor allowing a minimum of relative movement. This effect is not trivial - with a shorted length of cable and a DC current of a few 10's of amps - the motion can actually be felt! This in turn allows the wires to move respective to one another, and by doing so, dissipate a measure of energy. This obviously leads to a degree of distortion of the signal arriving at the speaker. To come to the point: I do not worry at all about the above effect. Still I would suspect that this effect is notably stronger (and perhaps even *measurable*!) than esoteric effects relating to HI-end mains cable, or "played-in" interlinks with designated in and outputs. It amazes me that this rather obvious effect seems not be discussed in hi -end circles. (or is it?) It has been discussed, but as with all other cable-related non-linear distortions, it has also been quantified at less than -140dB below a 10 amp rms signal, hance hardly of consequence for audio. I *have* seen microphonic effects in small-signal cables, but that's an entirely different mechanism, and well understood by those who make studio-grade microphone cables (as opposed to the 'high end' brands which just have cable made up by Belden etc.). To come to the final point (finally): why are very subtle mechanisms of distortion so magnified in the various discussions - and an obvious mechanism like described above is scarcely heard off? Largely because all cables sound the same, so you have to make up *some* kind of wacky theory to advertise your 'special' brand! -- Stewart Pinkerton | Music is Art - Audio is Engineering |
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Speaker wire - another fine theory
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Speaker wire - another fine theory
On 6 Sep 2003 14:55:36 GMT, René wrote:
On 4 Sep 2003 15:43:43 GMT, (Stewart Pinkerton) wrote: It has been discussed, but as with all other cable-related non-linear distortions, it has also been quantified at less than -140dB below a 10 amp rms signal, hance hardly of consequence for audio. I *have* seen microphonic effects in small-signal cables, but that's an entirely different mechanism, and well understood by those who make studio-grade microphone cables (as opposed to the 'high end' brands which just have cable made up by Belden etc.). The -140 dB claim seems realistic to me, and I continue to be unworried :-). Yet, this effect is at least measurable, contrary to some other interlink-related effects I have seen mentioned - this places the considered effect in a degree of importance an order of magnitude higher! ..so what is the cost of rigid coax nowadays... About a buck a foot. Such 'cable' is standard issue for microwave use, consisting of a copper tube, a solid copper wire centre conductor, and solid Teflon dielectric. It's kinda tricky to work with, but it looks *really* cool! :-) -- Stewart Pinkerton | Music is Art - Audio is Engineering |
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Speaker wire - another fine theory
"Stewart Pinkerton" wrote in message
... On 6 Sep 2003 14:55:36 GMT, René wrote: On 4 Sep 2003 15:43:43 GMT, (Stewart Pinkerton) wrote: It has been discussed, but as with all other cable-related non-linear distortions, it has also been quantified at less than -140dB below a 10 amp rms signal, hance hardly of consequence for audio. I *have* seen microphonic effects in small-signal cables, but that's an entirely different mechanism, and well understood by those who make studio-grade microphone cables (as opposed to the 'high end' brands which just have cable made up by Belden etc.). The -140 dB claim seems realistic to me, and I continue to be unworried :-). Yet, this effect is at least measurable, contrary to some other interlink-related effects I have seen mentioned - this places the considered effect in a degree of importance an order of magnitude higher! ..so what is the cost of rigid coax nowadays... About a buck a foot. Such 'cable' is standard issue for microwave use, consisting of a copper tube, a solid copper wire centre conductor, and solid Teflon dielectric. It's kinda tricky to work with, but it looks *really* cool! :-) Come on, tell the real truth...its sounds okay ;-) -- Stewart Pinkerton | Music is Art - Audio is Engineering |
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Speaker wire - another fine theory
René wrote in message news:dJo5b.342490$o%2.157128@sccrnsc02...
Please allow me to introduce (yet) another mechanism of distortion: Speaker wires can carry substantial AC currents, which in turn generate measurable magnetic fields. As the "+" and "-" wires are usually positioned side by side, some mechanical forces are working on them. The plastic (?) isolator material is somewhat elastic, therefor allowing a minimum of relative movement. This effect is not trivial - with a shorted length of cable and a DC current of a few 10's of amps - the motion can actually be felt! This in turn allows the wires to move respective to one another, and by doing so, dissipate a measure of energy. This obviously leads to a degree of distortion of the signal arriving at the speaker. To come to the point: I do not worry at all about the above effect. Still I would suspect that this effect is notably stronger (and perhaps even *measurable*!) than esoteric effects relating to HI-end mains cable, or "played-in" interlinks with designated in and outputs. It amazes me that this rather obvious effect seems not be discussed in hi -end circles. (or is it?) A *true* High ender is henceforth expected to use loudspeaker wiring with spreaders that keeps the conductors well apart lest he will not be taken seriously. To come to the final point (finally): why are very subtle mechanisms of distortion so magnified in the various discussions - and an obvious mechanism like described above is scarcely heard off? Disclaimer: if somebody makes money out of this idea - I like to have a fair sha-) I have encountered this phenomenon examining some twin 10 inch nearfield monitors in a recording studio. They had been wired with 2.5 mm solid core mains distribution cable. The electromechanical vibration of the cable was easily felt. Exchanging the cable for a more conventional multistrand kind produced no obvious change in the response of the speaker although the cable vibration was no longer noticable. Steve Lane |
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Speaker wire - another fine theory
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Speaker wire - another fine theory
I agree that ANY wire carrying a current has a magnetic field
surrounding it.. What I meant was that the copper itself would not be magnetized to cause the wire to vibrate. -MIKE |
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Speaker wire - another fine theory
"---MIKE---" wrote in message
news:6VN7b.408943$YN5.275543@sccrnsc01... I agree that ANY wire carrying a current has a magnetic field surrounding it.. What I meant was that the copper itself would not be magnetized to cause the wire to vibrate. Actually, any two wires conducting current regardless of conductor material will feel a force to due to conservation of energy. With AC excitation like in a speaker wire the force between the two wires will pulsate. If you're designing pulsed energy weapons with millions of amps you have to account for the forces involved lest your wiring structure rip itself apart. Any emag textbook will show you how to calculate the forces involved. As for home speaker wires it's probably on the order of the force of a gnat fart. Sure it might inject electrons into the signal from the change in capacitance (conductor spacing) but what's a few femtoamps when you have amps of signal? Bob Pease did a paper a few years ago on this relating to measuring very low input bias current opamps. Motion in the wiring (due to vibrations in the room) injected enough electrons to mess up the measurements. Of course, they were trying to measure currents literally of a few thousand electrons per second. Once current increases into the picoamp or nanoamp range the effect is not measureable. |
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Speaker wire - another fine theory
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Speaker wire - another fine theory
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Speaker wire - another fine theory
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Speaker wire - another fine theory
On 16 Sep 2003 14:42:59 GMT, (ShLampen) wrote:
In article , (Stewart Pinkerton) writes: So what? Electromotive force is still generated, which causes the wires to vibrate. I would bet that most of this motion (if any) is caused by the PHYSICAL vibration of the speaker itself. Are you saying you can feel it at the amplifier output? I'm not saying that it has any *significant* effect whatever, simply that the effect exists, even if only at the microscopic level. I'm *certainly* not suggesting that there's any *audible* effect, as I hope regular readers will understand! -- Stewart Pinkerton | Music is Art - Audio is Engineering |
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Speaker wire - another fine theory
On 16 Sep 2003 14:44:33 GMT, (ShLampen) wrote:
In article , (Stewart Pinkerton) writes: I *have* seen microphonic effects in small-signal cables, but that's an entirely different mechanism, and well understood by those who make studio-grade microphone cables (as opposed to the 'high end' brands which just have cable made up by Belden etc.). Now what does this mean? We make good mic cables for ourself but poor cables for private labeling? Not what I meant at all, simply that many of the 'high end' brands (as you well) know, are simply rebadged Belden cable, possibly with the addition of a fat and colourful outer jacket. I have the greatest respect for Belden cables, and I apologise if I was unclear on this point. I don't think that's accurate. We've been making cable for 101 years and microphone cable since electrical recording came in, so I doubt there's any cable effect we don't know about and take into consideration with each new design. I'm sure that's the case, and I've certainly never seen any of the amazing 'science' quoted by Cardas, MIT et al in the Belden catalogue! -- Stewart Pinkerton | Music is Art - Audio is Engineering |
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Speaker wire - another fine theory
In article , ShLampen wrote:
In article , (Stewart Pinkerton) writes: So what? Electromotive force is still generated, which causes the wires to vibrate. I would bet that most of this motion (if any) is caused by the PHYSICAL vibration of the speaker itself. Are you saying you can feel it at the amplifier output? Actually, the force can be calculated. This is a high-school level physics calculation. I'll avoid the derivation and simply show that the force between two parallel conductors carrying a current is calculated as: F/L = u0/(4 pi) 2I^2/r where F/L is the force per unit length, u0 is the permability of free space, close enough for this purpose, I is the current (and the I^ term assumes that the currents are of equal magnitude) and r is the distance separating them. Indeed, the definition of an ampere, the fundamental unit of current, is in terms of the force between two parallel wires carrying equal currents: "An ampere is that constant current which, when flowing in each of two infinitely long parallel wires that are 2 meter apart in a vacuum produces a force on each wire of 2*10^-7 newton per meter of length" Semat, Fundamentals of Physics, Holt, Rinehart & Winston, 4th ed. Now, 1 amp is sufficient current to produce 8 watt into a nominal 8 ohm loudspeaker load, so that gives us a good basis on which to make some calculations. The separation of the conductors in a typical 10 gauge zip-cord style speaker wire is on the order of 5 mm, or 0.005 meters. Since the force on each goes as the inverse separation, we would expect the force top be 200 times that if the conductors were separated by 1 meter, so that the total force is: 200 * 2 * 10^-7 newtons/meter or 4 * 10^-5 newtons/meter per conductor, or a total net force of 8 * 10^-5 newtons/meter. That's 0.00008 N/m the force exerted by a 1 gram weight due to the acceleration of gravity at the earths surface is, (since F = m*a) F = 0.001 * 9.8 m/sec^2 or 9.8 * 10^-3 newtons. That's 0.0098 N, call is 0.01 N. Let's put this into perspective. A standard U. S. one cent coin (a penny) has a mass of 3 grams and weighs in, therefore, at 0.3 newtons. To generate the equivalent force of that 1 ampere current along 1 meter of wire, we'd have to take that penny, chop it into about 350 individual pieces, draw each piece (weighing about 8 micrograms each) into a wire 1 meter long, and carefully lay it on top of the insulation so that the wire is compressed under that heavy burden. Now, using the softest PVC insulation imaginable, let's estimate its mechanical compliance is on the order of about .1 mm/N/cm of length, or, thus, about 0.001 mm/N/m of length (just did a VERY rough measurement). We can now calculate the total displacement of the conductors in such a wire. simply: x = F * C where x is the displacement in meters, F is the applied force in newtons and c is the mechanical compliance in meters/newton. In our case, since F = 8 * 10^-5 n/m and C = 10^-6 m/n/m, then x = 8*10^-5 n * 10^-6 m/n/m x = 8 * 10^-11 meters that's 80 TRILLIONTHS of a meter. The radius of a hydrogen atom is on the order of 10^10 meters, so we're talking about movements comparable to atomic dimensions for fairly sizeable currents. -- | Dick Pierce | | Professional Audio Development | | 1-781/826-4953 Voice and FAX | | | |
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Speaker wire - another fine theory
ShLampen wrote:
In article , "Mike Gilmour" writes: Ok do some serious testing then market a speaker cable that is 'motion' free (take that in its literal sense) then laugh all the way to the bank No, no! Solid concrete speakers. Better yet, build the speakers into the foundation for the house (takes multi-room audio to a new level). Of course it better be OXYGEN FREE concrete. Feh. Concrete is for wimps. The real men use cast iron. |
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Speaker wire - another fine theory
"Rusty Boudreaux" wrote in message ...
"ShLampen" wrote in message ... In article gzy5b.260113$cF.82096@rwcrnsc53, (Richard D Pierce) writes: I believe you are wrong here. Inductance is determined by the size of the wire, not the distance between them (that would be capacitance). I can show Dude, you need to go back to school. Inductance is proportional to the enclosed loop area. Increase the spacing and you increase the inductance. Capacitance decreases with separation. I believe it is you, Mr Bordreaux, who needs to go back to school. A straight wire's inductance will decrease as the diameter increases. Bob Stanton |
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Speaker wire - another fine theory
In article ,
Bob-Stanton wrote: "Rusty Boudreaux" wrote in message ... "ShLampen" wrote in message ... In article gzy5b.260113$cF.82096@rwcrnsc53, (Richard D Pierce) writes: I believe you are wrong here. Inductance is determined by the size of the wire, not the distance between them (that would be capacitance). I can show Dude, you need to go back to school. Inductance is proportional to the enclosed loop area. Increase the spacing and you increase the inductance. Capacitance decreases with separation. I believe it is you, Mr Bordreaux, who needs to go back to school. A straight wire's inductance will decrease as the diameter increases. Double dude, go back to reading class, that's NOT what we are talking about at all. We are talking about the effective series inductance of a LOOP. In other words. Take a speaker wire, with its two conductors. Measure the inductance of the whole shebang. Now, separated the two conductors of the speaker wire by a large distance, say, insted of them being 5 mm apart and in parallel, separate them so that they now are 1 meter apart save where they connect to the amp and speaker. Measure the inductance. It will be different. How? (Hint: inductance is a function of enclosure loop area, which we just changed by a whole bunch). -- | Dick Pierce | | Professional Audio Development | | 1-781/826-4953 Voice and FAX | | | |
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Speaker wire - another fine theory
"Bob-Stanton" wrote in message
... "Rusty Boudreaux" wrote in message Dude, you need to go back to school. Inductance is proportional to the enclosed loop area. Increase the spacing and you increase the inductance. Capacitance decreases with separation. I believe it is you, Mr Bordreaux, who needs to go back to school. A straight wire's inductance will decrease as the diameter increases. Bob Sattnon, How about actually reading what we are discussing. Steve Lampen (ShLampen) made two assertions: "Inductance is determined by the size of the wire, not the distance between them (that would be capacitance)." and "Speading out each conductor is one way to reduce inductance." His first assertion was wrong and the second was actually backward (assuming he meant spreading instead of speading). I corrected both of his assertions by pointing out increasing the SPACING and thus increasing the loop area will increase the inductance. Did I, at any point, say anything about the wire diameter? But since you brought it up, which effect is more pronounced? Take a typical speaker wire and double the conductor diameter while keeping the separation between the two the same. Now take the original wire and increase the spacing by one conductor diameter (i.e. the center of the conductors will be at the same location as the case with larger diameter wire). Now, which case (bigger wire or more separation) has a larger inductance? |
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Speaker wire - another fine theory
On 18 Sep 2003 14:36:22 GMT, (Stewart Pinkerton)
wrote: On Wed, 17 Sep 2003 18:09:09 GMT, (Bob-Stanton) wrote: (Stewart Pinkerton) wrote in message Goertz MI has very low impedance, around 6-8 ohms, and very high capacitance, while the classic spaced construction cable, 'balanced' FM antenna feeder, has 300 ohm impedance and very high inductance. Agreed that we're talking a lot less than milliHenries here. Actually, if the Goertz cable (or any other) is terminated in it's characteristic impedance, it will not look capacitive or inductive to the amplifier. It's terminal impedance will be a pure resistance. Yes, but that isn't ever going to happen with a loudspeaker, except at a very few specific frequencies. True, but using a decent 8-ohm cable even with a real speaker will yield an impedance (forgetting the speaker itself) that is very, very close to a resistive 8 ohms. It certainly will not be the highly inductive load of a traditional twin-flex speaker cable. Of course some amplifiers need that additional inductive load to stay stable, but that is another story. d _____________________________ http://www.pearce.uk.com |
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Speaker wire - another fine theory
"Rusty Boudreaux" wrote in message news:gv9ab.489808
How about actually reading what we are discussing. Steve Lampen (ShLampen) made two assertions: "Inductance is determined by the size of the wire, not the distance between them (that would be capacitance)." and "Speading out each conductor is one way to reduce inductance." His first assertion was wrong and the second was actually backward (assuming he meant spreading instead of speading). I corrected both of his assertions by pointing out increasing the SPACING and thus increasing the loop area will increase the inductance. Did I, at any point, say anything about the wire diameter? Lampen was referring to the 'size' of the wire. That is diameter or gage, right? But since you brought it up, which effect is more pronounced? Take a typical speaker wire and double the conductor diameter while keeping the separation between the two the same. Now take the original wire and increase the spacing by one conductor diameter (i.e. the center of the conductors will be at the same location as the case with larger diameter wire). Now, which case (bigger wire or more separation) has a larger inductance? In the first case, doubling the diameter of speaker wire would reduce the loop inductance. In the second case, doubling the wire spacing would increase the loop inductance. In the a real world both you and Lampen are wrong. Real speaker cables typically have a 75 Ohms characteristic impedance. This is true for both large and small gage cables. The characteristic impedance is a function of the ratio of the wire's inducatance and capacitance, not it's absolute size. A large speaker cable (12 gage) will typically have a characteristic impedance of 75 to 120 Ohms. If an 8 Ohm termination is connected to the end of a 20 ft long, 12 gage speaker cable, the impedance that the amplifier will see (at 20KHz) will be 8.096 + j 0.189. A 20 gage speaker cable (of the same 75 Ohms characteristic impedance) will have an impedance 8.196 +j 0.189. The resistive component of the impedance of the small speaker cable, will be slightly higher, but the inductive component will be exactly the same. Therefore both large and small speaker cables, can have the same inductance. So, if you are saying a larger gage speaker will always have more inductance, you are wrong (sorry). Lampen was also wrong when he said it would have less inductance. Bob Stanton |
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Speaker wire - another fine theory
On 18 Sep 2003 16:14:04 GMT, Don Pearce wrote:
On 18 Sep 2003 14:36:22 GMT, (Stewart Pinkerton) wrote: On Wed, 17 Sep 2003 18:09:09 GMT, (Bob-Stanton) wrote: (Stewart Pinkerton) wrote in message Goertz MI has very low impedance, around 6-8 ohms, and very high capacitance, while the classic spaced construction cable, 'balanced' FM antenna feeder, has 300 ohm impedance and very high inductance. Agreed that we're talking a lot less than milliHenries here. Actually, if the Goertz cable (or any other) is terminated in it's characteristic impedance, it will not look capacitive or inductive to the amplifier. It's terminal impedance will be a pure resistance. Yes, but that isn't ever going to happen with a loudspeaker, except at a very few specific frequencies. True, but using a decent 8-ohm cable even with a real speaker will yield an impedance (forgetting the speaker itself) that is very, very close to a resistive 8 ohms. No, it won't. Anyone who has dabbled in radio will tell you that you need at least tolerably close load matching to get anything like a proper resistive transmission line. Now, since the amplifier certainly won't have anywhere close to 8 ohms source impedance, and the speaker won't be anywhere near to an 8 ohm resistive load over the vast majority of its working range, you are in fact back to the lumped capacitance model. It certainly will not be the highly inductive load of a traditional twin-flex speaker cable. Of course some amplifiers need that additional inductive load to stay stable, but that is another story. A reality check will indicate that a few dozen microHenries (as you'd get for ten feet of 'zipcord') hardly constitutes a 'highly inductive load', even at 20kHz. -- Stewart Pinkerton | Music is Art - Audio is Engineering |
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Speaker wire - another fine theory
On 19 Sep 2003 16:32:15 GMT, (Stewart Pinkerton)
wrote: On 18 Sep 2003 16:14:04 GMT, Don Pearce wrote: On 18 Sep 2003 14:36:22 GMT, (Stewart Pinkerton) wrote: On Wed, 17 Sep 2003 18:09:09 GMT, (Bob-Stanton) wrote: (Stewart Pinkerton) wrote in message Goertz MI has very low impedance, around 6-8 ohms, and very high capacitance, while the classic spaced construction cable, 'balanced' FM antenna feeder, has 300 ohm impedance and very high inductance. Agreed that we're talking a lot less than milliHenries here. Actually, if the Goertz cable (or any other) is terminated in it's characteristic impedance, it will not look capacitive or inductive to the amplifier. It's terminal impedance will be a pure resistance. Yes, but that isn't ever going to happen with a loudspeaker, except at a very few specific frequencies. True, but using a decent 8-ohm cable even with a real speaker will yield an impedance (forgetting the speaker itself) that is very, very close to a resistive 8 ohms. No, it won't. Anyone who has dabbled in radio will tell you that you need at least tolerably close load matching to get anything like a proper resistive transmission line. Now, since the amplifier certainly won't have anywhere close to 8 ohms source impedance, and the speaker won't be anywhere near to an 8 ohm resistive load over the vast majority of its working range, you are in fact back to the lumped capacitance model. I do mean close. With the line being a minute fraction of a wavelength long, You would be very hard pressed to measure the speaker alone as any different to the speaker plus line (once the line delay has been normalised) even at the frequencies where the speaker is quite some way from 8 ohms. Normal speaker cables, around a couple of hundred ohms, can make a measurable difference - a fact attested to by the instability of some amplifiers using them What I am really trying to do here is dispel the myth that such cables (like the Goertz) are in some way capacitive when driving a speaker. The fact is they aren't. It certainly will not be the highly inductive load of a traditional twin-flex speaker cable. Of course some amplifiers need that additional inductive load to stay stable, but that is another story. A reality check will indicate that a few dozen microHenries (as you'd get for ten feet of 'zipcord') hardly constitutes a 'highly inductive load', even at 20kHz. Inductive enough to pull a poor amplifier back from the brink of oscillation, though. d _____________________________ http://www.pearce.uk.com |
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Speaker wire - another fine theory
On 19 Sep 2003 17:53:15 GMT, Don Pearce wrote:
On 19 Sep 2003 16:32:15 GMT, (Stewart Pinkerton) wrote: Anyone who has dabbled in radio will tell you that you need at least tolerably close load matching to get anything like a proper resistive transmission line. Now, since the amplifier certainly won't have anywhere close to 8 ohms source impedance, and the speaker won't be anywhere near to an 8 ohm resistive load over the vast majority of its working range, you are in fact back to the lumped capacitance model. I do mean close. With the line being a minute fraction of a wavelength long, You would be very hard pressed to measure the speaker alone as any different to the speaker plus line (once the line delay has been normalised) even at the frequencies where the speaker is quite some way from 8 ohms. Well yes, due to the 'line' being a very small fraction of a wavelength, as you say. Normal speaker cables, around a couple of hundred ohms, can make a measurable difference - a fact attested to by the instability of some amplifiers using them That is due to the series inductance of the cable, not the characteristic impedance per se. Stick a milliHenry inductor on the front of some 8-ohm Goertz MI, and you get the same result. What I am really trying to do here is dispel the myth that such cables (like the Goertz) are in some way capacitive when driving a speaker. The fact is they aren't. The fact is, they are. Try hooking an original Naim NAP250 to some Goertz MI, and watch it fry! It certainly will not be the highly inductive load of a traditional twin-flex speaker cable. Of course some amplifiers need that additional inductive load to stay stable, but that is another story. A reality check will indicate that a few dozen microHenries (as you'd get for ten feet of 'zipcord') hardly constitutes a 'highly inductive load', even at 20kHz. Inductive enough to pull a poor amplifier back from the brink of oscillation, though. Yes, as noted above. -- Stewart Pinkerton | Music is Art - Audio is Engineering |
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Speaker wire - another fine theory
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Speaker wire - another fine theory
(Stewart Pinkerton) wrote in message ...
On 18 Sep 2003 16:14:04 GMT, Don Pearce wrote: On 18 Sep 2003 14:36:22 GMT, (Stewart Pinkerton) wrote: On Wed, 17 Sep 2003 18:09:09 GMT, (Bob-Stanton) wrote: (Stewart Pinkerton) wrote in message No, it won't. Anyone who has dabbled in radio will tell you that you need at least tolerably close load matching to get anything like a proper resistive transmission line. That is because at RF, the cable is usually many wavelengths long. A cable will act as an impedance transformer, if the load is other than the cable's characteristic impedance. As for audio, a 20 ft long cable is only 406 E-6 wavelengths long (at 20 kHz). This is far too short to cause an impedance transformation. Therefore, the impedance seen by the amplifier will be nearly the same as the impedance of the load (loudspeaker). A cable will add a tiny amount of resistance and inductance, but that will usually be insignificant. Now, since the amplifier certainly won't have anywhere close to 8 ohms source impedance, and the speaker won't be anywhere near to an 8 ohm resistive load over the vast majority of its working range, you are in fact back to the lumped capacitance model. Trying to analyze a transmission line, (even a short one like an audio cable) by using lumped constants, will always result in wrong answers. Bob Stanton |
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Speaker wire - another fine theory
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Speaker wire - another fine theory
(Stewart Pinkerton) wrote in message ...
On 22 Sep 2003 22:30:59 GMT, (Bob-Stanton) wrote: (Stewart Pinkerton) wrote in message ... On 20 Sep 2003 15:15:37 GMT, (Bob-Stanton) wrote: (Stewart Pinkerton) wrote in message As I recall, Dunlavy rated his ribbon cable as 6 Ohms characteristic impedance. That cable would have a slightly capacitive loop impedance with an 8 Ohm load. Indeed he did, and the Dunlavy cable was/is probably the most *technically* excellent speaker cable ever made. OTOH, John Dunlavy also noted that it was audibly indistinguishable from 'zipcord', even on his top studio monitors (which were 4-6 Ohm loads). Yes, I agree. You will notice I *never* said 6 Ohm ribbon cable sounded better than zip cord. (In this thread I was writing about how the inductance of cable changes with spaceing, not how various cables sound.) Most people would be *better off* with zip cord than with expensive ribbon cable. Many amplifier designs include a small inductor in the output. This inductance improves stability. Zip cord is slightly more inductive than ribbon cable, which is an advantage not a disadvantage. Bob Stanton |
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Speaker wire - another fine theory
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