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Tech Square Technical and speculative discussion of amps, cables and other topics. |
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Tech Square Technical and speculative discussion of amps, cables and other topics. |
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In Reply to: Re: Hmmmmm...Hi Jon posted by Jon Risch on September 25, 2003 at 21:09:01:
""Doing better thank you, but still not so great overall.""JRA mixed bag..But I hope the path is not too long..
JE..[ The rate of change of current causes internal eddy currents, which force re-distribution of the current density..If strand to strand contact is compromised, those eddy currents will be reduced, and the current will drive FURTHER into the bundle..As if the bulk resistivity of the conductor were reduced. ]
JR: Of course, your statement asimes significant impairment of strabnd to strrand contact, but the real world has it5 sonmewhere in between, with the potential consequenes I point out.
ME: My statement was that it is opposite of what you wrote..the loss of interstrand conductivity will REDUCE the skin effect.
JR: You are saying that strand jumping is going to be initiated by the self-inductance of the wire?
ME: No, I'm saying that each wire will carry current based on what it sees magnetically as well as just the voltage difference at the ends..A good example is a six around one cable, six wires spiralled around the middle one..All six external wires see the exact same magnetic environment, the middle one sees no net field as a result of the six outer ones. At DC, the current distribution of the seven will be based solely on their endpoint resistance, but when the wire is energized by an AC signal, the inner wire doesn't see the time rate of change magnetic field the six outer ones do.
We have that problem hugely magnified in one of our superconducting magnet cables...there, with no resistance, the current within the wires is entirely determined by the rate at which we ramp the current, and the inner wire can actually have current flowing opposite of the six outer ones.
JR: Yep. But the maun point is that a larger wire, like teh 12 ga., vs. the much smaller wires, like the 20 ga., will have more driving force behind the strand jumping, and therefore, more potential deleterious effect from any such strand jumping.
ME: In theory, yes..I point out that the equations being used are incorrect for the app...not totally wrong, but wrong levels.
JR: I note for the record, that these equations were also used by AH, in an article which yiou proof read, and ostensibly approved and gave yiour blessing to. I never saw one comment along these lines then. I still say yougo out of your way to questuion pro=-cable physics, and deliberately ignore the HUGE amoubnt of questionable science touted by the naysayers. Perhaps it is a true blind spot, and you can not even see you are doing this.
ME: I note for the record: The equations used at AH are the ones used by all, me included... What also must be noted is this: I suddenly realized when posting a response to you that buried in the scot's guide article was the caveat of the 5 depths thing. So, that is indeed a new realization for me as well. And, you're statement also does not hold water based on my response to TM on dielectric stuff, where I stated something like "the article has not proven burn in doesn't exist"..
(I must note: It has always been my belief that the differences of opinion I, you, JC, peter, se, TM, JJ..etc..is the best thing for this forum (and others)...without it, I personally would never have realized the equations being used are mis-applied..I learned something also..)
So, I hadn't commented on the skin eq. error, as I didn't realize it till recently. In other words, there is no "conspiracy of silence" on my part..
JR: I have never been one to try and relate skin effect issues to HF amplitude losses, which is all your concern about conductance is.
All I have ever said about skin effect (or if you prefer, self-inductance) is that it makes the surface of the wire more critical with regard to platings, finish, etc., as well as providing a potential mechanism for strand jumpingm, and why I think that the larger stranded wires ar going to get into more trouble than the smaller ones.
ME: Didn't you do a sweep showing .4 db loss at 20Khz?, or something like that?
I prefer using both terms; skin effect and self inductance are related, but separate entities..
Bad surface conditions on stranded wires reduces skin effect...strand jumping will only be an issue with radial gradients, that only happens when intercepted changing mag fields are different.
JR: Then I would hope that you would also not recommend the Audioholics articles that have the very same skin effect equations in them, and atempt to cite skin depths, hard numbers and draw conclusions from them.
Me: They have used real equipment, real wires, real results, and real reproducibility by anyone around the world...which I always admire and look for. I do understand that GDS views this forum, and if he feels the equations should be updated, then that's cool..I noted the error of equations, but point out that real world effect would only be a little less than what was previously expected via the equations..so, that would only head in the direction of less concern.
JR: ""The Audioquest site article has some basic explanation of teh theory of strand jumping, and a nice graphic to help illustrate the situation, and this is why I point folks there, not for the worlds greatest physics lessson.
Come up with a nicely worded explanation/description, a nice graphic, and I will use it from now on.""
Yah, I liked the graphics also..cool pics..
I personally don't think any of us understands it enough to commit to "paper"...yet..
Cheers, John
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Follow Ups
- Re: Hmmmmm...Hi Jon - jneutron 08:03:31 09/26/03 (1)
- Re: Hmmmmm...Hi Jon - Jon Risch 10:26:38 09/26/03 (0)
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