Importance of cable shielding and inductance

[Michael5039]

Now obviously the most important things with cables is resistance, and obviously doubling the cross-sectional area quadruples the conductivity and halving the length doubles it. So that part is really easy to know what to do with regards to speaker cable, use the shortest and thickest cable possible.

But, I dont know much about how to deal with inductance and shielding. As far as I'm aware foil and braiding are the standard methods of shielding, so how important/effective are they? What reduces inductance and how important is it to care about?

Also what is the deal with twisting cables? Surely that just increases the overall length slightly?

With regards to terminations, is it best to get banana plugs which can be crimped and soldered with shrink wrap to reduce the likelihood of corrosion and decrease contact resistance? I dont see much of the locking banana plugs about in the uk, are they new?

I know it would be easiest just to go with what is recommended on here but unfortunately brands like blue jeans arent really available in the UK.

 

[highfigh]

Now obviously the most important things with cables is resistance, and obviously doubling the cross-sectional area quadruples the conductivity and halving the length doubles it. So that part is really easy to know what to do with regards to speaker cable, use the shortest and thickest cable possible.

But, I dont know much about how to deal with inductance and shielding. As far as I'm aware foil and braiding are the standard methods of shielding, so how important/effective are they? What reduces inductance and how important is it to care about?

Also what is the deal with twisting cables? Surely that just increases the overall length slightly?

With regards to terminations, is it best to get banana plugs which can be crimped and soldered with shrink wrap to reduce the likelihood of corrosion and decrease contact resistance? I dont see much of the locking banana plugs about in the uk, are they new?

I know it would be easiest just to go with what is recommended on here but unfortunately brands like blue jeans arent really available in the UK.

Ever look at telephone wires? They're twisted, with no braid or foil. They tend to be thin (23 or 24 ga), solid and in the average house, they're old. Sometimes, they're extremely old. And you know what? They still work as conductors and the noise-rejecting properties still work.

Twisted pair works on the principal that opposite polarity signals cancel each other and this is part of what's called 'common mode' rejection. When current "flows' in a wire, it causes a magnetic field. The magnetic field from one of the wires in the pair meets the opposing field and its strength diminishes to the point of not being a problem.

Banana plugs make connecting/disconnecting easy, but that's about all they do. They were originally designed for use in laboratories and testing facilities, but they work well for other uses. Cables carrying signals like audio and video usually use RCA plugs and jacks or XLR, although XLR were originally used for pro and commercial uses.

Where you are and what you have access to doesn't matter as much as whether the cable is built to suit the application.

For a good explanation about cable types and shielding, Blue Jeans has a group of articles-

http://www.bluejeanscable.com/articles/index.htm

 

[Speedskater]

Almost never are speaker cables shielded/screened. A pro audio expert, reports that shielding or even attaching speaker cables to metal beams can make even good amplifiers unhappy.

Twisting speaker cables will do two things:
1] Reduce the possibility of picking up RFI interference.
b] Reduce the cable's self inductance, which will ever so slightly increase the treble response.

 

[Michael5039]

I know Banana plugs are more a thing of convenience rather than sound quality. But, I read about it being a good idea to protect the cable from oxidation which will definitely damage the sound quality. That does make a lot of sense to me. Also the locking Banana plugs do sound like a solid connection, so the advantage of corrosion protection and convenience surely make them worthwhile? Just is making sure they're crimped and soldered a waste of time or does it make a difference?

So while twisting them might no make so much difference, there is a reason they do it. Okay that makes a lot of sense to me. But why would shielding have a negative affect? I dont understand that? Seems like an outrageous claim to me? Where does this pro audio expert report this claim?

 

[TLS Guy]

I know Banana plugs are more a thing of convenience rather than sound quality. But, I read about it being a good idea to protect the cable from oxidation which will definitely damage the sound quality. That does make a lot of sense to me. Also the locking Banana plugs do sound like a solid connection, so the advantage of corrosion protection and convenience surely make them worthwhile? Just is making sure they're crimped and soldered a waste of time or does it make a difference?

So while twisting them might no make so much difference, there is a reason they do it. Okay that makes a lot of sense to me. But why would shielding have a negative affect? I dont understand that? Seems like an outrageous claim to me? Where does this pro audio expert report this claim?

First of all shielding a speaker cable is unnecessary. If you put a shield round a cable, you have conductors between insulation. So you have created a capacitor, as insulators are dielectrics. Now speakers are low impedance, four ohms usually. Unbalanced cables usually terminate at 10 Kohms and balanced at 500 ohms. Both of these are much higher than four ohms. So the shunting capacitance of a cable is much more significant across a 4 ohm load, than a 500 or 10 Kohm load.

Now some amps are unstable with a capacitor across the speaker terminals. They will go into fierce supra sonic oscillation and often destroy themselves and very likely your tweeters. In addition depending on the dielectric constant of the insulator, the capacitance easily could impair HF performance.

There may be others, but the only amps I know that are unconditionally stable into capacitative loads, are Quad amps, as Peter Walker invented the electrostatic speaker back in the 50s and Quad have produced electrostatic speakers since then.

That is why you don't see, and should not see, shielded speaker cables.

 

[WaynePflughaupt]

Typically only low level audio or video signals need shielded cable, which is why line-level signals use – guess what? – shielded cables. Amplifier outputs are a high-level signal and as such fairly impervious to EMI or RFI. If speaker cables needed shielding, then such cables would have been the defacto standard from the dawn off transducers. As long as you avoid long runs in close proximity and parallel to power cables, you’re fine.

Perhaps some of the other more knowledgeable folks here can confirm, but AFAIK speaker wire oxidation typically is only superficial – i.e., on the surface of the wire and not riddled through and through. And I think it will typically be a situation with low-grade copper wire, not oxygen-free wire that’s often used for audio applications.

I’ve never seen a need for locking banana plugs. Regular ones with decent build quality have a good pressure connection, I’ve never had a problem with them. A screw connection is just fine. Just make sure and re-tighten them after a year or so. Soldering heavy-gauge speaker wire to a thick-metal banana plug can be a challenge and will likely end up melting the cable’s vinyl jacket.

Regards,
Wayne A. Pflughaupt

 

[Michael5039]

I guess shielded cable is not very common in the US then but the 'better' cables over here in the uk are often shielded. For instance my Chord Carnival Silverscreen cable on my hifi has an incredibly thick insulator and foil round the outer most layer. I had previously thought this was a good cable untill now Im doubting that haha.

I guess you are right by saying you create a capacitor but sure the capacitance is so low it wouldn't even matter? Surely when you're talking about capacitors damaging amplifiers you're talking about a capacitance of actual significance ?

As for oxidation that definitely is a thing, I've certainly seen it myself. Having no oxygen in the copper I assume means Oxide free and is purified through electrolysis. That wont stop the rest oxidising, the issue is the copper exposed to the air, all copper exposed to air, will oxidise.

 

[TLS Guy]

I guess shielded cable is not very common in the US then but the 'better' cables over here in the uk are often shielded. For instance my Chord Carnival Silverscreen cable on my hifi has an incredibly thick insulator and foil round the outer most layer. I had previously thought this was a good cable untill now Im doubting that haha.

I guess you are right by saying you create a capacitor but sure the capacitance is so low it wouldn't even matter? Surely when you're talking about capacitors damaging amplifiers you're talking about a capacitance of actual significance ?

As for oxidation that definitely is a thing, I've certainly seen it myself. Having no oxygen in the copper I assume means Oxide free and is purified through electrolysis. That wont stop the rest oxidising, the issue is the copper exposed to the air, all copper exposed to air, will oxidise.

I guess that is why your cable has such a thick insulator, to lower the capacitance. The thinner the insulator the higher the cap value. In any event shielding a speaker cable is nonsense. Someone is selling a "bill of goods".

I just read their puffery and its bunk. You don't need to spend 6.2 GBP per meter for speaker cable. In fact any 16 AWG or thicker cable at the hardware store is likely better.

 

[WaynePflughaupt]

As for oxidation that definitely is a thing, I've certainly seen it myself.

Really? What does it look like? Perhaps you can post us a link to a picture. About the only thing I’ve seen is something like the copper turning a slightly darker color vs. being bright and shiny. Again, it’s only superficial and will have no affect on sound quality, which should be obviously as only the outer circumference of the wire is exposed to the air. Cut the wire and you will see no oxidation inside.

Regards,
Wayne A. Pflughaupt

 

[TLS Guy]

Really? What does it look like? Perhaps you can post us a link to a picture. About the only thing I’ve seen is something like the copper turning a slightly darker color vs. being bright and shiny. Again, it’s only superficial and will have no affect on sound quality, which should be obviously as only the outer circumference of the wire is exposed to the air. Cut the wire and you will see no oxidation inside.

Regards,
Wayne A. Pflughaupt

I have never seen it either. However it is possible he had product from China and it might be adulterated copper. I had personal experience with the Chinese not knowing the correct formula for plumbing grade brass. More likely they knew, but cheated by adding more zinc and less copper, plus illegal quantities of lead!

In the UK they have the insidious VAT. Therefore goods are more expensive and it encourages junk. I can tell you from personal experience that on the whole goods are of a far lower quality than the US. We have enough junk, but it is out of control over there.

 

[highfigh]

It can be helpful for people to indicate their location when they ask questions, as in the original post. Cable requirements and availability aren't the same all over.

If corrosion is a problem, the bare wires can be dipped in dielectric grease and the excess removed before inserting in the terminal, as long as it's not being soldered.

Shielding is needed to keep outside sources of noise from affecting low level signals. Using general terms, the output from an amplifier going to a speaker can be anywhere from just under 3V (1W, 8 Ohm load) to more than 100V (1250W, 8 Ohm load) and it takes quite a bit of interference to affect the signal but as TLS mentioned, the shield makes the wire's characteristics into a capacitor and that's a problem. As voltage increases, cable dimensions need to change, too.

 

[highfigh]

I have never seen it either. However it is possible he had product from China and it might be adulterated copper. I had personal experience with the Chinese not knowing the correct formula for plumbing grade brass. More likely they knew, but cheated by adding more zinc and less copper, plus illegal quantities of lead!

In the UK they have the insidious VAT. Therefore goods are more expensive and it encourages junk. I can tell you from personal experience that on the whole goods are of a far lower quality than the US. We have enough junk, but it is out of control over there.

Maybe the insulation was PVC- the clear lamp cord that was so common until about 1980 often turned dark or in some cases, green. Didn't seem to need contact with other harsh chemicals, either.

 

[Swerd]

Contrary to widespread belief, oxygen-free copper is not produced for the benefit of the audio trade. However, that doesn't stop it from becoming a major advertizing feature for speaker cable sellers.

Wire made from oxygen-free copper or from standard copper both oxidize at the same rate. And yes, the oxidation occurs on the surface of the wire where it gets exposed to air. With the gauges of wire commonly used for speakers, surface oxidation makes little difference in conductance, and has no audible effect.

 

[Michael5039]

I'll find a picture in a bit if I can, bit busy at the moment, but yeah it goes darker, and eventually green. If you want a good example of oxidised copper look at the statue of liberty. They have to use a sacrificial anode to stop it corroding any further as far as Im aware, so the copper 'steals' electrons off the sacrificial metal if you understand the chemistry of that?

I dont know how much it affects anything to be honest but it affects the contact resistance which is normally one of the largest forms of resistance in a circuit, so it seems stupid to me to take care to choose a very low resistance cable then dismiss the contact resistance of the oxidised copper.

 

[Swerd]

I dont know how much it affects anything to be honest but it affects the contact resistance which is normally one of the largest forms of resistance in a circuit, so it seems stupid to me to take care to choose a very low resistance cable then dismiss the contact resistance of the oxidised copper.

Yes the oxidation of copper, at the point of contact, is a large source of resistance. If it worries you, once a year cut off a bit of the wire where the old contact was made with the speaker terminals. Remove insulation to expose fresh wire, and reattach it to the speakers.

You can do that with bare wire connections, or with banana plugs or spade terminals if they attach by screws.

 

[highfigh]

I'll find a picture in a bit if I can, bit busy at the moment, but yeah it goes darker, and eventually green. If you want a good example of oxidised copper look at the statue of liberty. They have to use a sacrificial anode to stop it corroding any further as far as Im aware, so the copper 'steals' electrons off the sacrificial metal if you understand the chemistry of that?

I dont know how much it affects anything to be honest but it affects the contact resistance which is normally one of the largest forms of resistance in a circuit, so it seems stupid to me to take care to choose a very low resistance cable then dismiss the contact resistance of the oxidised copper.

That's not oxidized copper on the Statue Of Liberty, that's Copper Chloride-

http://www.google.com/imgres?imgurl=http://www.skylighter.com/images/web_pictures/Copper-Chloride.jpg&imgrefurl=http://www.skylighter.com/mall/product-details.asp?id=2489&h=198&w=255&tbnid=fNcYZKZBQDeDxM:&zoom=1&tbnh=155&tbnw=200&usg=__qhE_lsH9Y0FQjqrHOIxDsHqUIeo=&docid=bqQIXl7loomblM&itg=1

Copper oxide looks like this-

http://img.tradeindia.com/fp/1/357/943.jpg

The sacrificial anode could be Zinc, Aluminum or Magnesium, which is used in marine applications to inhibit corrosion of metals when that damage would eventually cause the vessel to become inoperative. They're always on aluminum parts, such as out-drives and associated items, outboard motors, prop shafts and others. The zinc loses material more quickly because it's less 'noble' than the other, necessary metals. Obviously, when the metal that needs to remain is Aluminum, the anode would be one of the other metals.

 

[Audioklepto]

That's not oxidized copper on the Statue Of Liberty, that's Copper Chloride-

http://www.google.com/imgres?imgurl=http://www.skylighter.com/images/web_pictures/Copper-Chloride.jpg&imgrefurl=http://www.skylighter.com/mall/product-details.asp?id=2489&h=198&w=255&tbnid=fNcYZKZBQDeDxM:&zoom=1&tbnh=155&tbnw=200&usg=__qhE_lsH9Y0FQjqrHOIxDsHqUIeo=&docid=bqQIXl7loomblM&itg=1

Copper oxide looks like this-

http://img.tradeindia.com/fp/1/357/943.jpg

The sacrificial anode could be Zinc, Aluminum or Magnesium, which is used in marine applications to inhibit corrosion of metals when that damage would eventually cause the vessel to become inoperative. They're always on aluminum parts, such as out-drives and associated items, outboard motors, prop shafts and others. The zinc loses material more quickly because it's less 'noble' than the other, necessary metals. Obviously, when the metal that needs to remain is Aluminum, the anode would be one of the other metals.

Wow, I've been reading this forum for years. Finally the subject strays into my realm... more or less.
Most of highfigh's post is correct, zinc coatings are sacrificial coatings.
Oxidation is an electrochemical process that requires an oxidizer as well as something to be reduced. The oxidizer does not have to be oxygen. Mineral acids come to mind, but there are many others. As for the green patina on the stature of liberty, copper makes a chloride, sulfate and oxide, but they are all quite water soluble and will wash off in the rain. The patina is most likely copper nitrate, as it is not very soluble in water.

 

[3db]

Contrary to widespread belief, oxygen-free copper is not produced for the benefit of the audio trade. However, that doesn't stop it from becoming a major advertizing feature for speaker cable sellers.

Wire made from oxygen-free copper or from standard copper both oxidize at the same rate. And yes, the oxidation occurs on the surface of the wire where it gets exposed to air. With the gauges of wire commonly used for speakers, surface oxidation makes little difference in conductance, and has no audible effect.

The exaggeration of oxidation is yet another one of these myths running a muck amongst the audiophile community. If oxidiation has that much of an effect on the resistance of the conductor and in turn affects the sound, then one or more of following conditions must be present;

1. Poor electrical connection/contact to the speaker/amp terminals to begin with
2. The gauge of wire is too narrow for the length of run being used.

I have had connections for years at a time without any affect in sound. Yeah the outer layer was a little darker but I didn't hear one bit of difference in sound once I had cleaned up the wire.

 

[MALIK_BRODER]

Wikipedia on Speaker Cables has a great article that shows what´s required in a cable. In a nutshell, for most applications with speakers placed at a reasonable distance from the amp, simple lamp cord works fine. Of course this is for speaker cables, component cables are a different animal due to much lower signal to noise.