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From somewhere in cyberspace someone wrote the following yesterday,"Here is how an AC signal travels in a coax cable. Note the signal does not flow in the center conductor. Note the signal does not travel back and forth from the source to the load. Rather it travels in one direction from the source to the load outside the center conductor through the insulation, dielectric."
So, the question, gentle readers, is this comment in quotes:
1. Completely correct.
2. Partially correct, if so which part(s)?
3. Completely or almost entirely incorrect
Edits: 05/02/22 05/02/22 05/02/22Follow Ups:
I vote 3
A coax cable is identical to any other in that the currents flowing in the two paths as a result of a load at the far end, are ALWAYS equal but opposite.
Coax cable is a configuration that has the least resistance and inductance because the magnetic fields the current in the conductors produce,, do not escape (and become a series L). The geometry of RF cables is aimed at having a particular ratio between the series L and parallel C which when more than around 1/2 electrical wavelength long,. give the cable an impedance of say 50 Ohms. That impedance can be made higher by making the center conductor smaller in diameter and the diameter of the shield larger (reducing the parallel C) TV coax is usually 75 Ohms vs 50 Ohms for say RG-8 radio cable.
Coax is not glamorous but low loss and more flexible variants of RG-8 works great for speaker cables, all the parameters are better and if the cable is long enough they begin to matter so far as effecting the loudspeakers output.
From paragraph in my original post,"The signal does not travel in the center conductor."
"The signal travels in one direction only, from source to the load."Please comment.
Edits: 11/05/22 11/05/22 11/05/22
So perhaps we are talking about two different views, a more conceptual one, like the signal travels in one direction from the source through the system, to the speaker.
What i am talking about is how that "signal" is transferred via wires as a current and voltage through two paths or a pair of conductors to the loudspeaker. Where the current that makes the voice coil move and produce sound is traveling equally in both conductors but in opposite directions and if a coax is used, equally on the inner and outer conductors.
To have a complete circuit, where a signal can be transferred electrically, you need both paths, with AC like audio one is positive when the other is negative. "Ground" is often used for one of those paths.
The paragraph I quoted was mixed up to a certain extent. That paragraph was actually referring to the energy contained in e and B fields located outside the conductor. The Poynting vector energy flux points in the direction of free electron motion. Current and voltage are scalar quantities so they do not travel or have any direction. What does travel and have direction are the free electrons, the moving charges. Free electrons are physical entities whereas current and voltage are not. This will become important on discussions of directionality.
Edits: 11/07/22 11/07/22
AC does flow back and forth in a coax cable or it would not be AC.
Current doesn't flow back and forth, technically speaking. Current is a scalar quantity, it has no direction, it has no velocity, it's calculated according to amount of free electron flow, total charge per unit time. Only the free electrons move back and forth in an AC circuit. The picture of how electricity works is further complicated by adding the concept of Poynting vector and energy flux outside the conductor in electric and magnetic fields. Having said that we're stuck with common occurrence of term, "alternating current."
Edits: 01/17/23 01/17/23 01/17/23
2. partially correct.
Near field vs far field.
In the near field more of the energy feeds back to the source. Further down a transmission line, that effect becomes more negligible.
The electrical *power* is contained in the electric and magnetic fields that extend outside of the conductor. But is the *power* the same thing as the *signal*? For audio the answer is almost certainly no. We know what produces the power. Power is a calculated quantity, based on current and/or voltage, and so is current a calculated quantity. Current is calculated from the moving charges, I.e., the free electrons. So, what's the signal?Furthermore, electrical power is a scalar quantity and thus has no direction. Same with current.
Now, electric field and magnetic field ARE vector quantities, but their directions are perpendicular to the direction of the electron motion.
Edits: 08/07/22 08/07/22 08/07/22 08/07/22
Hopefully there will be enough left over signal power after transmission line losses there is still enough energy left to adequately power the load. The signal is the power delivered to the load. Are you talking about at the driver, or at the reciever? I'm not really too sure about superconducting coax but there is usually insertion loss with most cables.
In an AC circuit such as a speaker cable is part of there are two wires involved, + and - . The free electron motion direction on one wire is always opposite to the electron motion on the other wire at any given point in time. This motion of electrons is referred to as "moving charges." Alternating moving charges, and moving charges = current. The Moving Charges induce an electric field. The electric field moves along with the moving electrons, but very slightly since electrons move very slowly, but it does move.
It is that "moving electric field" that in turn produces a *magnetic field* - and this magnetic field interacts with the large permanent magnet attached to the speaker (and voice coil) and causes the speaker diaphragm to move outward and inward according to + and - wires. This back and forth movement of the speaker diaphragm occurs at the instantaneous frequency of the audio waveform that's being produced by the amplifier.
Here is how I learned it. Charges (moving or not) have an electric field. Moving charges induce a magnetic field. Accelerating charges causes changing electric and magnetic field which results in propagating em waves.
"The Moving Charges induce an electric field."
I don't believe Maxwells equation supports this idea.
Every time you change an electric field, you create a magnetic field. This is called the Maxwell-Ampere Law. We are not considering accelerating charges here. We are not considering stationary charges either. There are both E and B fields involved in this audio cable example. The E and B fields are perpendicular to the wire axis and perpendicular to each other.the Poynting vector is the cross product of E and B and represents the energy flux density. The E and B fields set up along the axis of the conductor and alternate E, B, E, B, etc.
Edits: 08/09/22
In an ac circuit, current changes direction when polarity changes. If you found a way to change the speed and direction of the flowing charges without first decelerating them then accelerating them in the other direction, you have discovered some new property of physics.
No, that's incorrect. The electrons change direction according to the audio waveform. That's why you need two conductors for each speaker cable, each conductor carries 1/2 of the audio waveform. The audio waveform is produced by the amplifier. What this means is that free electrons in the conductors change directions on both + and - as often as 20,000 times per second or more.Unlike AC out of the wall that alternates at 60 HZ the AC in speaker cables alternates at audio frequencies, 20-20k Hz. The electrons move back and forth at the instantaneous audio frequency whatever it may be.
When electrons move toward the speaker on one conductor they move in the opposite direction on the other wire and vice versa. That's how the speakers produce the acoustic audio waveform. The free electrons move only about one meter per hour, so there is no time to accelerate or decelerate. They only move about a millionth of an inch or so at a time. If you reverse the + and - wires on the speaker you reverse it's polarity.
Edits: 08/09/22 08/09/22
You keep changing the subject. You just made the claim, a couple posts ago, we are somehow supposedly not considering accelerating charges, in this discussion of yours about ac circuits. But now in this last post you seem to agree they are indeed changing velocity and ultimately direction. Again, how are you proposing this happens without accelerating these charges? New properties of physics discoverred right here in this very chat?
I have always said electrons change direction, that's the definition of an AC circuit. That's why it's called alternating current, because the electrons - the moving charges - alternate direction. And they do it at the rate of the instantaneous audio frequency. Your argument regarding acceleration is irrelevant. Since the electrons only move about one millionth of an inch at a time acceleration is irrelevant. The drift velocity is a constant, one meter per hour approximately. Take a DC for example - the electrons move at *constant velocity* of one meter per second. They don't accelerate.
Edits: 08/10/22
"The drift velocity is a constant"Incorrect. In an ac circuit the drift velocity changes sign when the signal polarity changes. These charges are no longer free, they are part of a signal if they have a drift velocity.
Of course it's significant. The magnetic field polarity reversal could not occur without it.
Edits: 08/11/22
Velocity and direction are two different parameters. Obviously electrons change direction, that's what I've been saying. Current has no direction. It's a scalar quantity. Duh!
In a waveguide, like a piece of coax, anything more than gozinta and gozouta drift "direction" is meaningless and the mathematics are perfectly adequately handled by adding a plus or minus a sign on the dirft velocity. These charges are not free. Duh!
You lost me dude. Of course the charges are moving - they're the free electrons. That's what current is - moving charges, moving electrons. Hel-loo! The electrons that are not free don't have anything to do with anything.Can I make a suggestion? Go back to whatever 2nd rate school you went to, assuming you went to school, which you probably didn't, and demand a refund.
This conversation can serve no purpose any more.
Edits: 08/12/22
Of course you are lost. Was there ever any question about that?BTW does your definition of "free" include trapped in an electric field such that there is literally only a single direction that may be travelled, based on the waveguide geomtry, until the signal polarity changes and then the only choice is travelling in the exact opposite direction?
Good grief, life in moronastan must be rough if that is really your idea of freedom.
Edits: 08/12/22
The energy flux density, I.e., the Poynting vector, is the cross product of the E and B fields that alternate with each other along the axis of the conductor. The E and B fields are orthogonal to the axis of the conductor and to each other. That's why it is said the "signal energy" lies outside the conductor. But it's also true that the E and B fields are produced by the motion of the free electrons. Which came first, the chicken or the egg?Recall there are two conductors in audio, + and - you can call them, each one Carrie's half the audio waveform, you could say. It's the alternating motion of free electrons that create sound in your room. Hel-loo! Try to escape your reality tunnel.
Todays tip: audio cables are not waveguides nor do they act like waveguides.
Edits: 08/13/22 08/13/22 08/13/22 08/13/22
Do you even slightly recall your original premise for this thread? Here is a reminder..."Here is how an AC signal travels in a coax cable."
Your attempts to divert the conversation to a talk about free charges was originally very very cute and all but as soon as we all realized it is a logical fallacy to change the subject and expect that to have some meaningful relevance I figured/hoped we'd all get bored with that and move back into discussing the originally promised subect.
"Todays tip: audio cables are not waveguides nor do they act like waveguides"
So now we are constrained to only be talking about audio frequencies are we? How convenient. Weird how you waited until now to mention it.
I know you may not be free like some of us but I will continue to refer to coax as waveguide just as the rest of the universe will, whether you are in agreement or not, since that is its typical usage.
Feel free to add DC to your coax, for all I care. Sounds like your local authorities are far more oppressive, however. You may want to watch it.
"But it's also true that the E and B fields are produced by the motion of the free electrons."
Correction: a charge has an associated E field regardless of whether it has achieved net motion due to an external field or not.
Correction 2: A charge trapped in an e field, which has been forced to travel in the path of a waveguide, at a resultant drift velocity, is not free.
Who cares about E or B field of free echarges? You?
Nothing of use occurs until until external fields are applied.
Is there some poynt you are trying to make?
Edits: 08/13/22 08/13/22 08/13/22 08/13/22 08/13/22 08/13/22
It appears you fell into my trap, I wanted to talk about audio cables all along. If you feel more comfortable talking about transmission lines and waveguides my suggestion is start your own thread. It appears you're not familiar with the Poynting vector as your so called corrections make no sense. Maybe you should research this whole subject, Google is your friend.Did you miss the subject line for this discussion, How electricity flows in an AC circuit?
What am I looking for? I'm looking for an answer to my oft repeated question, what is the audio signal in audio cables? In order to make design decisions on cables it would be helpful, important, to know what the "audio signal" is so that distortion and noise can be minimized.
Edits: 08/13/22 08/13/22 08/13/22
"so that distortion and noise can be minimized."
But you closed the conversation off to considering anything but coax. Why ignore an entire audio industries wealth of knowledge by immediately making off limits the industry standard circuit topologies designed to accomplish those exact goals?
You misunderstand. I only used the *quote* in my OP to raise the general subject of cables. More specifically audio cables. Obviously, I don't wish to limit the discussion to coax. Coax happens to be the cable used on the Wiki page for illustrating Poynting vector. It's just a jumping off Poynt. I'm primarily interested in audio cables, not "industry standard circuit topologies" What is the "signal" in audio cables? And how do internal and external forces affect the "audio signal?" How does the signal get distorted? If someone believes all cables sound about the same that's OK too.
Edits: 08/17/22 08/17/22 08/17/22 08/17/22 08/17/22
Seems like going out of the way to ignore industry topology trends, especially when wondering about best usage of something regularly used by the industry such as cables, you risk not seeing some important data points that could be valuable. For example, choosing a truly well balanced circuit and fully bipolar differential signals allows a certain level of noise and distortion rejection/cancelling completely unavailable to a system utilizing pure single ended/coax signals and hardware. You can still throw a picture of some twisted pairs in the fridge, you know.
Edits: 08/22/22
The trouble is that "industry standards" or "industry data points" - whatever that means - has little relevance to the discussion at hand. What industry are you referring to? The audio industry - specially the high end audio industry - has very few standards or requirements or regulations. There are no standards for polarity, wire directionality, fuses, power cords or cables. [NOTE: I'm not referring to function here, I'm referring to SOUND QUALITY.] Obviously a fuse must function to protect the electronics, for example. The debate is still on going regarding balanced vs unbalanced cables anyway. Ditto for shielded vs unshielded, or copper vs silver conductors. I'm not referring to theoretical functionality, I'm referring to SOUND QUALITY.There are no standards for sound quality, not the ones I'm talking about. Sure there are specifications, but that's not the same thing as sound quality as we know. The same cables or electronics or CD can sound radically different in different systems and different rooms.
The question remains: What is the "audio signal" in cables? If we knew what exactly were dealing with, what is being affected by internal and external factors, like RFI and vibration, we could build better fuses and cables. And even better amplifiers. I'm not referring to theoretical physics or electronics, or even functionality, I'm referring to SOUND QUALITY.
1. Audio waveform
2. Current
3. Electrons
4. Voltage
5.:Poynting vector
6. Magnetic field
7. Electric field
8. Electromagnetic wave
Edits: 08/23/22 08/23/22 08/23/22 08/23/22 08/23/22 08/23/22
Just couldn't figure out what industry I was referring to, eh? mmmhmmm fun game.
Who said anything about "sound quality", however it is you would have percieved such a thing? For all I know you are one of those people who likes more noise and distortion than the program material contains.
Earlier you said you wanted to find a way to achieve lower noise and distortion so I recomended balanced/differential..... Which *you* may still be debating the merits of....don't know, but others have quantified these things long ago. No doubt you will rationalize rejecting all existing empirical evidence with a goofy smile and a hand wave and that is AOK by me.
I just brought up sound quality. Does that surprise you? Why else would I be interested in the "audio signal" in cables and how to improve it? Why else would I say, once you can identify the "audio signal" in cables then you can go about trying to decrease the noise and distortion? I like your goofball comments, though. We're about through here, aren't we?
Edits: 08/24/22
Drift velocity is dependent on current
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Current is a calculated quantity. It's calculated based on the number of electrons in a given cross section of the conductor and the average drift velocity. I.e., moving charges. Current is also a *scalar quantity* - it has no direction. It doesn't move. The only thing moving are free electrons. Some electrons don't move in a straight line. That's why thicker conductors can carry more current as they say. So, actually current is dependent on the electrons not the other way around. Does that surprise you?
The distance vs. time that the electrons move (drift velocity) is dependent on the current.
More current = faster movement of the electrons but still very slow.
"Relation between Drift Velocity and Current Density
We can define current density as the total amount of current passing through a unit cross-sectional conductor in unit time. From drift velocity, we know the formula for drift velocity as:
I = nAvQ
J = I/A = nVQ
Where,
J is the current density measured in Amperes per square meter
v is the drift velocity of the electrons
Thus, we can say that the drift velocity of the electrons and their current density are directly proportional to each other. Also, when the electric field intensity increases, the drift velocity increases and the current flowing through the conductor also increases."
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Which came first the chicken or the egg?
I don't think the answer to that question changes this: "when the electric field intensity increases, the drift velocity increases."
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
It's the *average* Electron drift velocity that determines current. Current is a calculated value. Nothing I've said is contradictory. Obviously, since the electric and magnetic fields that alternate along the axis of the conductor represent instantaneous changes in audio frequency and amplitude they are *constantly changing.* I just described the E and B fields earlier today. You were possibly napping. You just can't seem to catch a break.
Edits: 08/13/22 08/13/22
What makes the speaker driver work? It's the interaction of the moving electric field carried by the speaker cable interacting with the large permanent magnet attached to the driver. Already we have established that the Poynting vector can't be the signal, mainly because it doesn't alternate directions. Furthermore the units of the Poynting vector is Watts per cubic meter. Yes, Watts per cubic meter. Dear readers, does that look like a signal to you? It's the power density.But what we have shown already is the audio waveform is the combined push and pull of the two + and - wires of each speaker cable. And what produces the electric field? That's the current, which is calculated according the number of moving electrons. So, at the end of the day electrons are really the "audio signal." The voltage produces the electric field and the current produces the magnetic field portions of the EM wave.bog course the e and m fields have vectors that are orthogonal to the direction of electron flow and to each other.
The Poynting vector is just a calculated value based on the electric and magnetic fields and points toward the speakers. But the Poynting vector doesn't produce the audio signal (waveform), the alternating current does. Just because the energy flows outside the wire does not mean the signal travels outside the wire. We have shown that the "signal" is actually the current so the "signal" does travel back and forth since it's an AC circuit. The Poynting vector is a red herring.
Edits: 05/03/22 05/03/22 05/03/22 05/03/22 05/04/22
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