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[ammitsboel]

I have a strictly technical question.

What is the conductance in silver, cobber and gold?
And what conducts best?

[ammitsboel]

Found this on the net:

Resistivity in ohm-meters
Metals:

           
Aluminum 2.65e-8

           
Beryllium 4.0e2.65e

           
Beryllium-copper

           
Brass 70% copper, 30% zinc

           
Copper 1.673e2.65e-8

           
Gold 2.35e2.65e-8

           
Iron 9.71e-8

           
Lead 20.648e-8

           
Magnesium 4.45e-8

           
Molybdenum 5.34e-8

           
Monel

           
Nickel 6.84e-8

           
Platinum 10.6e-8

           
Silver 1.59e-8

           
Stainless Steel-321

           
Stainless Steel-410

           
Steel, low carbon

           
Tin 11.0e-8

           
Titanium 42.0e-8

           
Tungsten 5.40e-8

           
Zinc 5.964e-8


So i guess i found what I was looking for.
Please post any comments you might have.

Best Regards

[Brian Roth]

Interesting, but why the question?  It becomes an issue when transmitting power from the utility company's "generator station" to your home, but is otherwise moot with audio (excepting loudspeaker wiring).

Bri

[ammitsboel]

My question was just out of curiosity.
And i had a discussion where one was claiming that copper was a better conductor than silver.

[Sahib]

Silver is the best conductor as it has the least resistance.

Top three conductors and their relative conductances are;

1.Silver 100%
2.Copper 98%
3.Gold 78%

Cemal

[Mike Mermagen]

Brian Roth wrote on Sun, 30 January 2005 08:17

Interesting, but why the question?  It becomes an issue when transmitting power from the utility company's "generator station" to your home, but is otherwise moot with audio (excepting loudspeaker wiring). Bri

Brian,
Since an entire audio chain is based on electrical signals over some kind of metal conductor, I'm not sure why you would say the point is "moot" for audio and not for loudspeaker wiring.

Mike

[David Satz]

Mike, [a] hi again, and it's because when you're feeding a signal to a relatively high-impedance load such as the input of a power amplifier, a few Ohms of resistance in the line won't affect the signal enough to matter. You can't hear a loss of, say, 0.001 dB even if it's frequency-dependent.

However, loudspeakers aren't a high-impedance load, so the impedance of speaker cable can become an appreciable fraction of their impedance--at which point the losses in the cable can become audible, or at least worthy of a thought.

It's basically Ohm's Law in action. If you've studied any electronics I don't want to start spelling that all out, but if you haven't, then we can certainly talk it through. At any rate it's an area of audio in which theory and practice (i.e. audible results) get along just fine.

--best regards

[Brian Roth]

Thanks, David, for voicing my exact thoughts.  I am VERY suspicious of claims made that a few/dozen feet of cable running analog line level signals can cause an appreciable degradation of the signal...unless it was built with "baling wire"  (or, in the Southwest where we have large ranches: "bob war"  AKA barbed wire  <g>).

I will allow that perhaps the insulation can have an effect due to capacitance loading, but that then puts the onus back at the device driving the cable.

But, I think there is some sort of Placebo Effect once someone pays $10/foot for fancy Oxygen-Free gold-plated wire with cross-twisted teflon insulation that has been pissed upon by vestal virgins under the new moon before being cryogenically (sp?) treated.  "By Gawd, I paid a FORTUNE for this cable, so it sounds GREAT!"

Bri

[ammitsboel]

Since this is a strictly technical forum the question was just strictly technical.
I don't think that the audible differences when comparing copper to silver is related to the conductance.
Maybe it can be measured by other parameters?

Best Regards

[Joe Crawford]

Actually, when you’re talking about cable used to transfer audio around the studio, there are four characteristics involved: resistance, capacitance, susceptibility to noise, and the fourth I think is (or at least used to be) called skin effect.  I think we all pretty well understand the effects of the first three.

If Dan is around maybe he can help me with the fourth one.  I’m a bit rusty on the skin effect.  I know that direct current is evenly distributed throughout the cross section of a conductor.  But, alternating current is different.  As the frequency of AC increases, the current tends to travel more in and along the surface of a conductor.  I know the skin effect has to be considered at radio frequencies, but does it also have a noticeable effect at audio frequencies?  Can we generally ignore it, or is it already covered by using the impedance of the cable?

Joe Crawford

[David Satz]

Joe, it can easily be shown that skin effect is several orders of magnitude below significance at all audio frequencies--even the highest audio frequencies that dogs and bats can hear--for all possible terrestrial cable lengths. For transmission lines carrying VHF and higher it's a different story. But with baseband analog audio it's not worth worrying about unless your cable is long enough to reach between planets--and then you might have some other problems to deal with, such as how to unkink it after a meteor shower.

Even baseband video frequencies aren't affected significantly unless transcontinental cables are your thing--and there again, I think that you might be more worried about sharks munching on your cable than high-frequency losses due to skin effect.

As a result I find that skin effect provides a good quick litmus test for rudimentary truth in advertising: If a cable manufacturer waves that particular bugaboo in front of you when talking about baseband analog audio cables, you can cross them off your list in a hurry.

--best regards

[Sahib]

Joe Crawford wrote on Mon, 31 January 2005 18:12

Actually, when you’re talking about cable used to transfer audio around the studio, there are four characteristics involved: resistance, capacitance, susceptibility to noise, and the fourth I think is (or at least used to be) called skin effect.  I think we all pretty well understand the effects of the first three. If Dan is around maybe he can help me with the fourth one.  I’m a bit rusty on the skin effect.  I know that direct current is evenly distributed throughout the cross section of a conductor.  But, alternating current is different.  As the frequency of AC increases, the current tends to travel more in and along the surface of a conductor.  I know the skin effect has to be considered at radio frequencies, but does it also have a noticeable effect at audio frequencies?  Can we generally ignore it, or is it already covered by using the impedance of the cable? Joe Crawford

Skin effect is the tendency of the alternating current to flow near or on the surface of the conductor at high frequencies. At 1Khz the current flows through the outside skin to a depth of 0.9mm. At 1Mhz the skin depth is 0.07mm. So it seems like it does not have a hugely concerning effect on audio frequency provided that the thickness of the conductor is sufficient to serve it.

Information is taken from my electronic tables and formulas.

[Joe Crawford]

Thanks David & Sahib.  That pretty well covers the skin effect.  And, it looks like Dan has covered impedance & termination in the ‘Word Clock, Super Click & Termination’ thread.

I feel much safer now in buying a few dozen more Munster cables.  Now if I can just figure out how to fit those #4 gage, gold twinaxes in my patch panels.  Wait, maybe it'll work better for mic cable if you don’t mind that welding shop look.  At least it'll be foot-proof.

Anyway, thanks again guys...

Joe Crawford

[danlavry]

The figures for skin depth you mentioned are for a specific wire gauge. The “mechanics” of skin effect is as follows:

There is an electrostatic force between electrons, and that force is making them “move away from each other”. You put a bunch of electrons in a conductor (such as a wire), and they want to keep separate from each other, while remaining inside the conductor, so they still will “even out” in terms of the spacing between them.

When you run DC down a wire, the same holds true. The cross section of the wire is “evenly distributed” in terms of electron spacing, so the whole copper gets used to conduct current.

But when you run AC, the electrons start moving back and forth, and the acceleration (and deceleration) of each electron produces a new force. This force is magnetic. The faster the acceleration (deceleration) the stronger the force. The combined force due to all the electrons makes the repulsion force at the center of the conductor be the strongest, and it gets weaker as you get away from center.

If it were only up to the magnetic force, all the electrons would end up right at the conductor surface. But the other force, the electrostatic one, does not let them be so near each other. The result is a balance between electrostatic and electromagnetic behavior. The electrostatic is a fixed force, the electromagnetic varies with frequency. The dependency on frequency is not linear – the skin effect goes up with the square root of the frequency (often expressed in MHz).

The dimensions of the wire (such as wire gauge, which relates to cross sectional area) do count. One way to relate to skin effect is as a multiplier of the DC resistance. The AC resistance will be the DC resistance multiplied by the square root of the frequency and also multiplied by a K factor. The K constant is different value for different wire gauges.

Say you have an 100 feet of an 18 gauge wire. The DC resistance is about 0.65 Ohms. The K factor for 18AWG wire is about 11. So the AC resistance is:
At DC .65 Ohms, at 20KHz it will become 1 Ohm, at 100KHz, 2.25 Ohm, at 1MHz we have 7 Ohms, 22 Ohms at 10MHz…

So yes, you may not want to use 100 feet of 18AWG for the speakers, but 10 feet is (0.1Ohm) probably fine, from skin effect standpoint. A 10AWG at 10feet yields DC resistance of 1 milliohm and with skin effect it comes to 4 milliohms, so even 100 feet of 10AWG is only 40 milliohms at 20 KHz (it is really 50 feet each direction).

Skin effect is “non capacitive” and “non inductive”. It is resistive only. No phase issues what so ever.

I guess one way to look at skin effect is through the “glasses of” “skin depth”. Skin depth is a bit of a simplification, an “average” because the wire is not really divided into 2 distinct zones (“electron flow zone” and “no electron zone”). A few electrons do run near the center, and the distribution is more gradual then a brick wall. But skin depth is a reasonable way to view skin effect.

Having said all of that, skin efect really does not matter for audio signals!

Regards
Dan Lavry
 

[Sahib]

danlavry wrote on Wed, 02 February 2005 19:24

Say you have an 100 feet of an 18 gauge wire. The DC resistance is about 0.65 Ohms. The K factor for 18AWG wire is about 11. So the AC resistance is: At DC .65 Ohms, at 20KHz it will become 1 Ohm, at 100KHz, 2.25 Ohm, at 1MHz we have 7 Ohms, 22 Ohms at 10MHz… So yes, you may not want to use 100 feet of 18AWG for the speakers, but 10 feet is (0.1Ohm) probably fine, from skin effect standpoint. A 10AWG at 10feet yields DC resistance of 1 milliohm and with skin effect it comes to 4 milliohms, so even 100 feet of 10AWG is only 40 milliohms at 20 KHz (it is really 50 feet each direction).

Dan,

Many thanks for this. Yes the formula book I have has limited info on this issue. Can you recommend me a better one? What do you use?

Regards,
Cemal