Propeller Head Plaza Technical and scientific discussion of amps, cables and other topics.

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Hmmmm.

Posted by jneutron (A) on July 7, 2003 at 20:46:20

In Reply to: Really Phil. posted by Jon Risch on July 7, 2003 at 19:08:43:

""How does the signal actually travel? An audio signal is an electromagnetic field, traveling along a conductive
circuit more like a train on a track than water in a pipe. Wait a minute, isn't the signal inside the wires, isn't it
current, and voltage? Well, yes and no. It could be argued equally well that the signal actually IS the EM field,
and that the current flow is merely a side effect.""JR

Nope..Where did you get that??? Oh yah, Hawksford...

Geeze, that article set e/m theory back 50 years...at least for those who read it and believe it..

It CANNOT be argued equally well that the signal is actually the e/m field, nor that the current flow is merely a side effect...please...

The TEM wave propogation is the degenerate form of the e/m field equations..It is the only one which requires two conductors. The TE and TM mode both can be supported within a cylindrical waveguide, the TEM cannot..

TEM field equations are satisfied with static field equations..In other words, the e field and mag field both are defined by static field definitions..

Hawksford neglected to consider the characteristic impedance of the parallel wire cable..He states that the dielectric supports the entire power flow..Just as you have parroted..BUT....How in the name of sam hill does the "power flow" in the dielectric make it past the amp binding posts, or the speaker binding posts??? To pass a TEM wave requires a continuity in the supporting dielectric...Not a pair of binding posts...Without the continuity, reflection of the power occurs... AND, the TEM wave will only propogate with the characteristic impedance of the line. So to split the insulation, or otherwise change the spacing of the conductors (like connecting them to the speaker) totally destroys any possibility of a TEM wave getting through, by destroying the characteristic impedance...

If you consider the speaker (load) as within a closed surface, and develop conservation of energy equations for that surface, with the wires penetrating that surface, you will find that the current within the conductors only, when multiplied by the voltage across them, will equal the power dissipated within the surface(heat flow plus mechanical energy) out of the surface..If the load is a resistor, them 5 amps of current into that surface with 10 volts across those wires, will introduce 50 watts of power to that volume..At no time, at any place, by anybody in the world, has that relation been proven incorrect. And at no time has the TEM "energy flow" within the dielectric of a speaker wire ever been considered in the measurement of that power flow.. If you, or anybody else on the planet can prove otherwise, I will pay for the tuxedo rental you will need when you meet the king of Sweden..

50 years of transmission line and waveguide theory, practice, and experience....totally ignored!!!!!Actually, now that I think of it, at least 55 years..

""The speed of the individual electrons is incredibly slow
compared to the EM field, which travels close to the speed of light, so it is the EM field that actually carries the
signal information.""JR

Again, incorrect...The e/m field equations provide the fastest possible carrying of the signal power. The rate at which that power flow can be changed at is the characteristic velocity of the cable, which is 1/sqr(lc). For e/m calculations, the speed is entirely dominated by the parameters of the lumped elements, the speaker, and any reactivity of the interconnect to current slew rates (skin) and voltage slew rates and levels (DA). The e/m field of a cable are parasitic entities.

If you want to really learn this stuff, I recommend either Jackson or Becker..I can give you the pub. dates and publisher if you so desire. And the relevant pages.

""A superconductor would behave in such a manner that virtually no current would flow inside of it, virtually no voltages would be detectable inside of it, as it's perfectly conducting nature would prevent the EM field from penetrating beyond the immediate surface, just deep enough to invoke the super conducting paradigm, and once the superconduction occurred, no further penetration would be possible.""JR

All superconductors have a characteristic known as J (sub) C. This is the critical current density of the material..The highest current density the material is capable of carrying prior to quenching.(which is also heavily dependent on the magnetic field intensity and it's direction).

When a superconductor is beginning to carry current, the outermost volume of the super begins to carry the current AT the current density Jc. The higher the current, the deeper the current has to flow so that the active cross sectional area of the conductor still carries Jc..For example, a Jc of 2000 amps/mm^2. At 2000 amps, the total area of the wire supporting current will be 1 mm square. At 4000 amps, 2 square mm will carry the current..When the current is high enough that the total area of the wire is used, quench will occur. For a 10 mm square area wire, that means 20 kiloamps will cause the wire to change from super to normal..

If the current does not force a quench, and it is removed, there will be circulating eddy currents within the wire that will remain forever, until the wire is raised above the critical temperature, where superconductivity stops. This effect, in combination with external or self induced magnetic fields, causes persistent currents and magnetic fields to remain.

And, there are no currently used superconductors in use that do not have an external metallic conductor sheathing..NbTi is typically either copper or aluminum..Nb/Sn is Cu or Al...Hts is typically silver. There are applications where we have to worry about skin effect occuring on the outer sheath, as copper typically increases conductivity by 1000 times, reducing skin depth tremendously. High ramp rates will not allow the current to get down to the super..

If you really wish to learn about that...I recommend Martin Wilson..I can give you more info on that.

TTFN, John

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