Cable shielding audiophool or facts?

[FriedMule]

Someone I know who is a wary big audiophool told me of a new "magical" solution for shielding cables and asked me if it works, but I have not enough knowledge to decide that, hope that you will help:-)

Imagine a cable. It has mounted a braided metal sleeve that are only connected to the amplifier, on top of that, there is a heat shrink tube and lastly a second braided metal sleeve only connected to the source. so that the two metal sleeves, separated by the heat shrink tube, makes a sort of capacitor with one leg on the amp and the other "leg" on the source, i.e. a CD-player.

Would that have any effect on EMI or RF?

EDIT: forgot to say that the one he has talked about is non balanced phono-cables, but my question is generel about that type og "magic" shielding:-)

[RandallMcRee]

If I understand correctly your diagram is wrong--shields need to be connected somewhere to be effective.

The text you describe actually makes some sense: cables that have shields connected at only one end are effective for shielding and avoiding ground loops. What you described is just two shields one connected at source and the other at destination.

Henry Ott in his treatise on grounding notes that this is an effective way to cut EMI. So, yeah, like most audiophile things there is a grain of truth. As always, though, these are typically bandaids to avoid diagnosing the root cause.

[FriedMule]

Great thanks for your answer, I know that my drawing dos not show the shields connection to the cabinets. I wanted to show the layering of the shields, not the connections. :-)

So this would work effective Agains EMI?
Do it work as a capacitor?
How effective is it?

[RandallMcRee]

Great thanks for your answer, I know that my drawing dos not show the shields connection to the cabinets. I wanted to show the layering of the shields, not the connections. :-)

So this would work effective Agains EMI?
Do it work as a capacitor?
How effective is it?

How effective? I don't know. Do some googling and figure this out yourself! Do some measurements! (In the Ott book there are a lot of variables noted, so a definitive answer is impossible w/out knowing specifics, e.g. no idea what your cable parameters are, the source impedance, etc. etc.).

As a capacitor, not effective at all--cable capacitance is a side effect of construction and is an impediment to the signal not a help. At audio frequencies, and for well-designed equipment, its a non-issue.

[Shock]

Sounds like audio triax or double insulated cable.

[CatalinaWOW]

The specific questions should be, "Is it more effective than standard shielding?".  Yes.  "How much better?". That will depend on many things, including frequency of the interference, spacing of the shields and several other things, but in most cases will be a few dB more or less.  "Does it matter?".  Again it depends.  There are many sources of noise in an audio setup.  They all add up to the noise floor in that setup with that recording.  If, as is usually the case the noise getting through a single shield is well below the other noise sources, the additional shielding makes no discernable difference to the sound, but the psychological effects of doing something exotic might be worth it.  You will think it sounds better whether it does or not.

Fixed an autocorrect foulup that made the middle part incomprehensible.  dB more became days before

[MosherIV]

  Would that have any effect on EMI or RF?

Ask your friend what effect rf has on audio frequency?

[AndyC_772]

RF being picked up on an audio cable can easily be demodulated and turn into an audible signal, there's nothing facepalm-worthy about that. Spend a few hours doing radiated immunity testing of (say) a wired telephone at an EMC lab if you don't believe me.

There's nothing special about a double shielded cable. Yes, they're a real thing, and no, they're not 'magic'.

Quite what the insulating layer between the two shields is meant to achieve is anyone's guess, though. It will form a distributed capacitor between ground and... ground. How is it supposed to be "better" in some way than having the two shields in contact?

[Towger]

Sounds like fairly standard double screened coax.

What I never understood is why audio fools insist on using 'magic' phono cables etc.  While 'Pro Audio' just uses balanced cables with 3 pin XLR.  Which cost less, are more robust, don't pickup much RFI etc.  Why spent all that money when pro equipment is in most cases cheaper.

[bson]

Audio cables don't have a ground wire, and use the shield for return currents, so even if they share mains ground this is not such a great idea.

[FriedMule]

Thanks for all your great answers:-)
To reply on some of your questions:

RandallMcRee "Why I do not look at google or messeure it by my self?" I have looked at google and got everything between "the solution to life" to "idiotic" and I have not yet a lab myself, on top of that I do not own that type of cable. So therefor I'd rather ask someplace that I trust (here).

Shock yes it looks a lot like it, except that the cable that I ask about was two core in the center and there is rubber heat shrink instead of the aluminium-foil.

CatalinaWOW and AndyC_772, the "magic" in this cable should be that on top of being a doble shielded cable, it would block nearly everything because the capacitor-effect should store the interference and when charged, block the non-DC interference like a capacitor blocks as AC.

MosherIV this is the beginner part of this forum, so facepalm-questions can happen.

Towger I think that the reason for many things audiophools do, is because they are audiophools:-)

bson I think that audiocable goes to ground via the outside negative wire that are often connected to the case?

[GregDunn]

Sounds like fairly standard double screened coax.

What I never understood is why audio fools insist on using 'magic' phono cables etc.  While 'Pro Audio' just uses balanced cables with 3 pin XLR.  Which cost less, are more robust, don't pickup much RFI etc.  Why spent all that money when pro equipment is in most cases cheaper.

Usually because pro equipment is designed to run at much higher signal levels than home/consumer gear, and your S/N will suffer when operated at consumer levels.  You would need to redesign all gain stages from the low level to the power amplifier in order to reap any benefit from balanced signals.  Using adapters between unbalanced and balanced segments of the audio path will either make no difference or possibly make it worse, depending on the equipment involved.  Also, I'm not sure if there are any consumer phono preamps with balanced I/O which cost less than pro gear - or whether they'd even matter.  Nearly all phono cartridges have a common ground so you're starting out with an unbalanced signal already.

[BrianHG]

RF being picked up on an audio cable can easily be demodulated and turn into an audible signal, there's nothing facepalm-worthy about that.

I once had a bad example of this where a poorly shielded setup would receive and demodulate a local AM radio station which had a super-strong broadcast tower a few blocks away.

As for balanced audio, yes, if all your hardware, source, pre-amp, amp is balanced and you want the extra SNR it can offer especially over long cabling, it is useful.  However, with just reasonable quality shielded cables, normal RCA should exceed what you are able to hear unless your AV equipment is crap, or you have a really severe ground loop to AC mains issue where mains signal with some received higher frequency noise is injected into your sound due to the nature and positioning of your household wiring just by overwhelming force.

[Richard Crowley]

I think that audiocable goes to ground via the outside negative wire that are often connected to the case?

What does that mean?
What is "outside negative wire"?
Does this audiophool have some sort of after-market bonding strap to all the chassis of his audio gear?
Surely you don't mean the green-wire safety-ground in the mains power cable.

If your proposed un-balanced tri-axial cable has only the center conductor connected from end-to-end,
then there is no return path for the audio signal and the cable won't work.
If you are relying on some external path as the return for the unbalanced audio signal, that is probably WORSE than just using a bog-standard ordinary RCA cable.

It is extraordinarily rare for someone to come up with a new, novel alternative way to do something invented 100 years ago.

[FriedMule]

I think that audiocable goes to ground via the outside negative wire that are often connected to the case?

What does that mean?
What is "outside negative wire"?

Sorry for my bad wording, what I mend was: "I think that audiocable goes to ground via the outside shield that also are used as the negative wire and often connected to the case?"

[Zero999]

Shielding can help guard against interference. It's normally used on very low level signals connected to the input, such as microphones, but can be used on the outputs too, as RF can get in there as well. Even signals outside the audio band can cause problems, as they can be demodulated by non-linear junctions inside the amplifier and produce audible noise.

The shielding doesn't have to be connected to earth to be effective. It just needs to be connected to the amplifier's chassis.

If you aren't experiencing any problems with noise or mains hum, then it should be left as it is and there's no need for additional shielding. If you are having problems with noise and hum, then start off with the signal inputs first. Before thinking about shielding, investigate whether it's caused by a ground loop. What external devices is the amplifier connected to? Are any of them also mains powered? Do you have anything connected to the amplifier, which is powered from the same DC power supply?

[FriedMule]

Hero999 Yes I have heard that a single shield can help with noise, but this "magic" cable postulates that a shield connected to source plus a outer shield connected to the amp, with a thin rubber insulator between, do miracles to the noise suppression because these two layers acts as a capacitor.

[Richard Crowley]

Sorry for my bad wording, what I mend was: "I think that audiocable goes to ground via the outside shield that also are used as the negative wire and often connected to the case?"

Sorry, that in no way explains how the ground return gets connected between the source and the destination. No amound of verbal description will get around this fundamental flaw in the logic.  Draw a circuit diagram and prove it for yourself.  This is 100% certified audiophool baloney. 

[FriedMule]

Richard Crowley lol love your comment and drawing:-)
As I see it, the only ground that both the source and amp has, is the ground via the power cable.
But the "magic" in this should be that one "leg" goes to one case and the other "leg" goes to the amp, as in a capacitor and thereby blocks noise like in a filter. :-)

[Richard Crowley]

Using the mains power protective earth (green wire) as the return path for your unbalanced audio signal is the very definition of a ground loop. This entire scheme is first class audiophool fantasy.  The co-axial shields DO NOT form any kind of "filter"  they only provide an open circuit for the audio signal. 

Construct a cable for yourself and try it.  Get back to us after you have actually tried a real example.  Otherwise, I am done with this absurd discussion.

[FriedMule]

So my reply to him is that it is BULL and even a heap of it:-)

[bson]

So my reply to him is that it is BULL and even a heap of it:-)

[AndyC_772]

CatalinaWOW and AndyC_772, the "magic" in this cable should be that on top of being a doble shielded cable, it would block nearly everything because the capacitor-effect should store the interference and when charged, block the non-DC interference like a capacitor blocks as AC.

Sorry, maybe it's a language thing, but this explanation just doesn't make sense.

Yes, the two shields together form a capacitor, in which both plates are connected to ground. Why is that a good thing? How and why does the presence of that structure have any effect on interference?

So my reply to him is that it is BULL and even a heap of it:-)

I think your reply should be in the form of a challenge. Explain why, using sound scientific principles, this cable should work better than simple co-ax.

Ignore anything vague or woolly. Insist on an explanation which refers to the well-understood principles of electromagnetic wave propagation.

[xavier60]

It is important for shielded connecting cables to have very low shield conductor resistance.
Any voltage drop that develops between the ends of the shield due to interference current  becomes input noise signal.
Even with double insulated AV components, there is always some capacitative interference current flow from mains to chassis.

[GrahamC]

What is described in the original post is called a Faraday shield, or more correctly in this case a cable with two Faraday shields where each in turn is connected to the chassis of the two connected pieces of equipment, one at each end of the cable and the two Faraday cages themselves are not connected to each other.

Faraday shields can be very effective at reducing EMI/RFI and ground loops but I have only used and seen where there is only one such shield on any given cable.

An interesting idea to use two. One can be quite effective but two may be a case of diminishing returns where the effort and cost of the second vs effectiveness  is not worth the time and effort.

cheers,