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In Reply to: Some interesting replies. posted by May Belt on April 17, 2007 at 02:50:57:
I don't prefer the "shock wave" analogy. Current flow is when electrons migrate. When the current is direct (DC) electrons do "flow", they migrate in one direction only. But in an alternating current with NO DC OFFSET, there is no net resultant migration - electrons simple migrate back and forth "about" where they were sitting before the voltage was applied. Although there are very short propagation delays in really long cable runs (transmission line theory), in wire runs as short as we find in home environments, the migration of electrons at the source end of a cable results in migration at the other end almost instantaneously.So, the better way to "think" about electron migrating in an alternating current is to picture electrons moving back and forth, in unison. Their relative displacement is proportional to the magnitude of current that is flowing, which is in turn proportional to the magnitude of the applied voltage, since impedance is constant (for a given frequency). In a 120V 60Hz branch circuit seeing 1A of current, electrons (according to my calculations) move back and forth about 0.4 X 10^(-6) or 0.4 micro-meters. 4.0 micro-meters at 10 Amps. So not very far in other words. The electrons basically just "sit and wiggle".
This is why I have trouble with the directionality theory, which in my mind is non-science based on the fact that some cables rely upon telescoping shielding techniques. Instead of labelling the cable "shield terminated this end" or "source end" and "load end", they put convenient little ARROWS on cables, making it intuitive to the layperson that the arrows should "point" AWAY from the source as 'everybody knows' that "music flows from source to load". The existence of these arrows make people think that if you try and "make music flow against the arrows" you're going to get bad sound. But music does NOT "flow from source to load". The only thing that could possibly affect the sound is changing the location of the termination point of the telescopic shield from source to load. But this has everything to do with shielding techniques and nothing to do with "directionality of conductors or dielectrics".
We just said earlier that electrons do not experience a net resultant migration (save for a very very small DC component) with audio signals - they vibrate back and forth. This is how interconnects and cables work: the "wiggle" at one end is the same "wiggle" at the other. Is the wiggle at the far end smaller due to voltage drop? No. The impedance is spread out evenly throughout the cable, so all of the "wiggles" are affected equally.
So, in any case, the fact someone painted arrows on a cable makes them no more directional than a frisbee that someone painted an arrrow on. If that were true, left handed people could not play frisbee.
I think the classic "Newtons Cradle" is a much better example of the "shock wave" model of energy propagation than an electric cable. Due to the short relative length of home audio interconnects and cables, they model much more like nodes than transmission lines.
Follow Ups:
John:Could you be more specific?
I didn't want to get into atomic energy levels and that good stuff. I just wanted to differentiate between DC and AC and provide a model that laypersons can relate to.
The point was that electrons don't really "flow" like water through a pipe.
It was not intented to be a discussion in quantum mechanics... ;)
Presto, If you REALLY want to understand how electrons flow, you have to go to advanced quantum based models in order to get a more accurate picture. You can't explain things away with a limited picture that is given to engineers and technicians. It just doesn't always work.
John:How "deep" you drill down into how something actually works depends on the intent of the model you are trying to create. We all know that everything around us is working within the laws and principles of quantum mechanics. But that does not devalue every model that science has made for us. Actually, to scrap all models we have at our disposal in science and just cite "quantum physics" is really where things are just being "explained away".
The bottom line is that after all that "quantum mechanics" talk is said and done, it still leads us to a differentiation between electrons, where the ones in the innermost orbits are referred to as bound electrons, and the more easily dislodged electrons in the outermost orbitals are referred to as free electrons.
Let's face it - almost every concept in science and mathmatics is a model of some sort. If it were not, quantum mechanics would be the ONLY language of science and it is not. I don't need to know what is going on at the atomic level when a white blood cell eats a bug do I? Do I need to account for the path of each electron when current flows? No. Almost all mathmatics based on current flow is based on some sort of model of current flow. We don't tally up the work done by each electron in it's crazy jittery path up and down energy levels and from atom to atom. There's too many of them to count, so we model the process.
I would entertain comments about where a model is insufficient or inaccurate, but to suggest 'models are useless and you need quantum physics' is really the only place where things are being "explained away" in my mind.
A model is not sufficient IF it does not explain everything that we see and hear. However, simple models are OK for everyday use. For example: I might say that the Sun rises each morning. This is known and appreciated by many across the world. However, we know that it is not an accurate model, just a convenient one that works most of the time, for the purposes intended.
At another level, we might say that the Earth and the Sun attract each other by the inverse square of the distance between them, and their relative masses. This is sort of true as well, but Einstein might have a slightly better model than this.
It is the same with electronic signal flow in a wire. The convenient models sometimes do not explain why we hear what we hear, so sometimes it is better to look deeper into the more exact models and see it we can correlate them with what we hear. That is why I have looked into more exact models of electron flow.
John:I thought at the atomic level, it's not really model anymore - it... is what it is! :o) I like mythbusters. Their models are often full scale, or not models at ALL (recreations of the real "claim".) Love that stuff.
In any case, so many models arrive at the conclusion that "what goes in must come out" when it comes to conductors. In fact, even the most definitive analysis of electron flow would come to this conclusion. But still, there are other factors. Modelling electrons going through a single wire is convenient, because it takes that pesky OTHER wire (the return path of the loop) out of the equation. :o)
I think this is where the impact of cable geometry and the relative positioning of the magnetic fields surrounding each conductor. Of course, with a very crude instrument (like a clamp on ammeter) the fields seem to be equal and opposite and cancel as one would expect. But clamp on ammeters - even tiny ones - cannot account for the magnetic interaction that is occuring BETWEEN conductors.
This then results in various schools of thought - you get the "twisters", the "shielders" and the "separatists". Some speaker cable designers go to great lengths to provide incredible levels of twisting (even insulting and twisting individual STRANDS) while others are claiming that ripping zip cord into its component parts and separating them by a few inches offers great improvements, improvements which will exceed any negative effects of the added inductance that the separation will cause. Even some of the most esoteric cable designs on the planet have large separations between the + and - conductors (Look at some of the Virtual Dynamics cables - some of their speaker cable topologies are reminiscent of hooking up a large arc welder!)
Yes, my biggest challenge when trying to learn about what constitutes an optimal conductor is trying to differentiate between truisms and mere pseudo-scientific claims borne of sheer marketing energy.
For the record, I am a really big fan of ultra-tight unshielded twisted pair (UTP) FEP teflon interconnects that are simply kept short and kept away from other fields. I think the whole audiophile community gets a little too hung up on shielding at times, and end up putting too much metal around their conductors. If triple-shielding of interconnects is necessary, I would be asking not if those interconnects are WORTH $1000, but why do I have so much noise to begin with, and why I am not shielding other parts of the signal chain in the presence of this "horrific level of magnetic interference" that warrants "triple shielding".
Just babbling now.
Presto, I cannot disagree with your wire choice.
Personally I find that there are two aspects to wire. One is geometry, the other is material purity and type. Sometimes, wire designers think one aspect is greater than another, but I think that they both can be important.
Back in the early '80's, I overheard a debate between Dr. Vandenhul (material quality) and Bruce Brisson (geometry). I finally heard some interesting discouse on the subject, yet that was about 25 years ago. Have we made much progress since then? I should hope to think so, but we are always condemned for even thinking that there is a difference, and being techninal at the same time. It slows things down to a crawl. ;-)
"Have we made much progress since then?"John:
I used to think things were done the way they were done because someone somewhere decided that was the best way to do it, and everyone else concurred! Then I had to grow up and realise that things like cost restrictions (or profit margin), space, simplicity, and most often sheer familiarity were why things are done the way they are done.
A good example is the widespread use of the unbalanced connection.
In consumer hi-end audio, it really is sometimes mind boggling how we generally obsess about "optimizing" something that was a compromise in the first place. Some guys refuse to play the game and build their systems around hybird amps and pre-amps (pro/hi-end) which are all balanced.
I have more balanced-to-unbalanced and unbalanced-to-balanced adapter cables than I usually care to admit.
Once I get more confident about my DSP based playback system (with built in EQ/Crossover and DRC impulse convolver) and get it sounding as musical and open as possible, I think I want to try an all-balanced preamp and amp section. I may even go to the extreme of running balanced out of Lynx 2B directly into amps with stepped attenuators. I am really not a fan of digital attenuation, even if small attenuation levels do not result in the dramatic dynamic range penalty as some folks make it out to be.
Anyways... babbling again! :^]
Presto, the theory that you gave here about electron flow, I learned as a college sophomore in 1961. It is not exactly how electrons flow.
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