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Thread: How fast does electricity travel?

  1. #1
    WBF Technical Expert (Speakers & Audio Equipment)/Member Sponsor [Technical Expert] garylkoh's Avatar
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    Lightbulb How fast does electricity travel?

    It's been a very intense couple of weeks, and the stresses of running a business would be overwhelming if it was not for great music and passionate fans. However, it feels like the last two weeks have been filled by shoddy suppliers, intractable customers, and the final straw was 2 hours in a debate over the laws of physics....

    So, here's another great use of the What's Best Forum - cartharsis. Instead of resorting to Angry Birds, I thought that I'd come back to something I enjoy and I've missed for the past 2 weeks.

    We can debate endlessly about whether you can hear/perceive something, but the laws of physics are immutable. It is absurd to argue that electrons travel at or anywhere near the speed of light because if anything is accelerated towards light velocity, its mass increases, and the mass will approach infinite mass as its velocity approaches the speed of light. To accelerate electrons or anything else to anywhere near light speed would require huge amounts of energy, and would approach infinity as we approach light speed.

    So, really, how fast does electricity travel?

    Let's talk about electrical current - which is defined as the ordered movement of charge. The charge that moves in a liquid or gas (non-conductors) could be an ionic charge, but we are concerned about electrons in a conductor.

    So, we can refine the question further by asking "how fast does an electron move in a conductor?"

    The unit of current is the Ampere. One ampere is defined as one Coulomb passing a given point in a circuit in a second. The Coulomb is the unit of charge that is equivalent to 6.25 x 10^18 electrons. That's a LOT of electrons, but electrons are very tiny.

    If we use copper as an example, copper has 8.5 x 10^22 atoms per cubic centimeter, and it has 1 mobile electron per atom. Since we know that the charge of a single electron is 1.6 x 10^-19 coulombs, we can easily work out the number of electrons that would need to flow past a point to have a single Ampere of current.

    The formula is so simple that it is trivial:

    V = I/(Q * e * R^2 x pi)

    where V = velocity of electron in cm/sec
    I = current in Ampere
    Q = number of mobile electrons per cubic cm
    e = electron charge
    R = radius of conductor in cm (12awg has radius of 0.1cm)

    V works out to 0.00234 cm/sec. That's 3.3 inches per day. The velocity of electrons is really slow.

    If you're playing music at an average of 2 Watts into a pair of 8 Ohm speakers - that's 0.5 Amperes. An electron (let's call him Fred) that goes into a pair of 9-foot speaker cable will take 130 days for Fred to come out the other side plus a few more days to travel through the voice coil, inductors, circuit board traces, internal wiring, etc.

    That's for copper. If the wire was silver, the electrons will flow slower. This is because both copper and silver have one free electron per atom, but silver is denser than copper, and therefore silver has more free charge carriers within the same cross section.

    However, why then can we pass such fast signals for music over wires? This is because it's not electrons moving that we are talking about, it's because the electrons are already in the wire waiting to move. Imagine having a pipe that is completely filled with marbles. When an extra marble is pushed in one end, a marble almost instantaneousness drops out the other end no matter how long the pipe is.

    The effect of electrical current is almost instantaneous (it cannot be instant) due to the domino effect of the electron charge carriers knocking on from atom to atom. Think of a row of dominos, with a gap in between. The larger the gap, the slower the knock-on effect.

    So, now we change the question to "how fast does electricity propagate through a conductor?"

    When the current flows, electrons move from atom to atom. As an electron is a charged particle, they have a force field (an electrostatic field or E-field). This field has a force associated with it, and a direction. So, when a current flows, there is an E-field radiating from the wire that flows with it.

    Also, when the current flows, a magnetic field (the H-field) is generated around the wire. The force of the electromagnetic field has a strength that is inversely proportional to distance (like the E-field) but is circular around the wire (the direction is according to the right-hand rule).

    When a current flows, the E-field and the H-field must rack together with the flow of current. No one field can get ahead and wait for the other to catch up. So, the issue is not how fast the electrons can move within the conductor, it is how fast the E- and H-field can travel in the medium it is travelling through (hence our interest in the dielectric around the conductor).

    Electromagnetic fields travel at the speed of light when in a vacuum (unlike an electron which is a particle, fields have no mass). They travel almost at the speed of vacuum in air, but slower in any other medium. The difference in speed is inversely proportional to the square root of the relative dielectric constant.

    For example, if the wire was insulated by water, which has a relative dielectric constant of 80, it will travel almost 9 times slower. Teflon has a dielectric constant of 2.1 - and hence will slow down the electrical propagation by 1.4 times.

    If you had a pair of speaker cables, one insulated by air, and the other insulated by teflon, there is no way that you can hear the difference in the speed of the cable. Even if it was insulated by water, the difference is way below any hope of perception.

    Light travels at about 300million meters per second.

    There is no way to argue that a cable is "faster" or "slower" based on speed of electricity in a conductor.

    So there..... better than therapy
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  2. #2
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    Do you think break-in has anything to do with the replacement of electrons in a cable or device? How much longer can the left speaker cable be than the right before one could audible tell a difference?

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    WBF Technical Expert (Speakers & Audio Equipment)/Member Sponsor [Technical Expert] garylkoh's Avatar
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    Quote Originally Posted by mojave View Post
    Do you think break-in has anything to do with the replacement of electrons in a cable or device?
    I don't think so - electron drift is so slow that to replace all the electrons in a cable will take years. Also, I don't think that you can distinguish between two electrons, so you can't feed in "better" electrons to replace the ones already there.

    How much longer can the left speaker cable be than the right before one could audible tell a difference?
    I don't like to have one cable more than 3 times longer than the other, but there is a minimum length at which I like to have speaker cables which is a bit longer than 1.5m. However, whether it is possible to reliably hear a difference is a totally different matter. At this point, being as stressed as I am, I couldn't hear a difference when earlier I blew the negative power supply rail of a new amp I'm designing...... so I'm not your best guy for this.

    Sorry....
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    VIP/Donor [VIP/Donor] microstrip's Avatar
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    Quote Originally Posted by garylkoh View Post
    (...) If you're playing music at an average of 2 Watts into a pair of 8 Ohm speakers - that's 0.5 Amperes. An electron (let's call him Fred) that goes into a pair of 9-foot speaker cable will take 130 days for Fred to come out the other side plus a few more days to travel through the voice coil, inductors, circuit board traces, internal wiring, etc. (...)
    May be here you should remember people who are waiting for its arrival, that since music is alternative current, Fred will take much, much longer to arrive ... Unless you are using a solid state DC coupled amplifier with an high offset!

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    Site Founder And Administrator Steve Williams's Avatar
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    Gary

    I have a lot of friends who believe that cables and connections take quite a while to anneal. Not sure I do however based on what you just posted I suppose that this could be reason to accept cables annealing to their connections
    Steve Williams
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    WBF Technical Expert (Speakers & Audio Equipment)/Member Sponsor [Technical Expert] garylkoh's Avatar
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    Quote Originally Posted by microstrip View Post
    May be here you should remember people who are waiting for its arrival, that since music is alternative current, Fred will take much, much longer to arrive ... Unless you are using a solid state DC coupled amplifier with an high offset!
    True that music is AC. However, when delivering a current, it is still measured the same way even if Fred keeps changing his mind. He goes, then he comes, then he goes, but still takes two steps forward and one step back.

    While we are talking about Fred.... electrons are negative and come from the ground. So, Fred is being sucked up from the ground by the amplifier and not pushed from the amplifier to the ground through the speaker.
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    WBF Technical Expert (Speakers & Audio Equipment)/Member Sponsor [Technical Expert] garylkoh's Avatar
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    Quote Originally Posted by Steve Williams View Post
    Gary

    I have a lot of friends who believe that cables and connections take quite a while to anneal. Not sure I do however based on what you just posted I suppose that this could be reason to accept cables annealing to their connections
    Steve,

    based on my own experience, cables and connections do take a long time to settle. I do find that solder joints take far longer to run in than crimped joints. So, your friends might be right that the connections anneal. Although, annealing based on electron drift might take thousands of years...... but I do hear cables and connections breaking in and sounding better.
    __________________________
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    Genesis Advanced Technologies

  8. #8
    So if I understood what you just said (a pretty big question), silver is not more/faster/better, fancy dialectics are not more/faster/better and even the length of the cable doesn't matter until you have a differential of 3 or more, what does make a difference?

    Tim
    In high-end audio, you can't even fight an opinion with the facts.

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    [WBF Founding Member] Gregadd's Avatar
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    Quote Originally Posted by Steve Williams View Post
    Gary

    I have a lot of friends who believe that cables and connections take quite a while to anneal. Not sure I do however based on what you just posted I suppose that this could be reason to accept cables annealing to their connections
    definitoin of anneal- http://www.merriam-webster.com/dictionary/anneal
    Be civil to all, sociable to many, familiar with few, friendly to one, and enemy to none.
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    WBF Technical Expert (Speakers & Audio Equipment)/Member Sponsor [Technical Expert] garylkoh's Avatar
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    Quote Originally Posted by Phelonious Ponk View Post
    So if I understood what you just said (a pretty big question), silver is not more/faster/better, fancy dialectics are not more/faster/better and even the length of the cable doesn't matter until you have a differential of 3 or more, what does make a difference?

    Tim
    Not exactly. What I am saying is that "speed" - either in terms of electron drift, or propagation velocity cannot be used to account for any conductor being faster or better.

    There may be other factors in play. For example, the capacitance of a pair of conductors in close proximity is directly proportional to the dielectric constant. However, we showed in the Cable Theory thread that the capacitance effects are too low to make a difference in the frequency response or phase response of a cable.
    Last edited by garylkoh; 05-25-2011 at 08:40 PM.
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