Cable shielding audiophool or facts? - Page 1
Forum section: electronics / beginners

author: FriedMule
author_rank: Frequent Contributor
timestamp: November 11, 2018, 10:51:16 pm
content: 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:-)

author: RandallMcRee
author_rank: Frequent Contributor
timestamp: November 12, 2018, 12:57:37 am
content: If I understand correctly yourdiagramis wrong--shields need to be connected somewhere to be effective.Thetextyou 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.

author: FriedMule
author_rank: Frequent Contributor
timestamp: November 12, 2018, 01:24:14 am
content: 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?

author: RandallMcRee
author_rank: Frequent Contributor
timestamp: November 12, 2018, 01:51:33 am
content: Quote from: FriedMule on November 12, 2018, 01:24:14 amHow 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.

author: Shock
author_rank: Super Contributor
timestamp: November 12, 2018, 01:56:08 am
content: Sounds like audio triax or double insulated cable.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: November 12, 2018, 02:15:14 am
content: 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

author: MosherIV
author_rank: Super Contributor
timestamp: November 12, 2018, 07:43:40 am
content: QuoteAsk your friend what effect rf has on audio frequency?

author: AndyC_772
author_rank: Super Contributor
timestamp: November 12, 2018, 08:02:16 am
content: 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?

author: Towger
author_rank: Super Contributor
timestamp: November 12, 2018, 09:21:33 am
content: 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.

author: bson
author_rank: Unknown
timestamp: November 12, 2018, 09:49:55 am
content: 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.

author: FriedMule
author_rank: Frequent Contributor
timestamp: November 12, 2018, 05:25:13 pm
content: 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?

author: GregDunn
author_rank: Frequent Contributor
timestamp: November 13, 2018, 12:29:04 am
content: Quote from: Towger on November 12, 2018, 09:21:33 amUsually 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.

author: BrianHG
author_rank: Super Contributor
timestamp: November 13, 2018, 12:40:45 am
content: Quote from: AndyC_772 on November 12, 2018, 08:02:16 amI 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.

author: Richard Crowley
author_rank: Super Contributor
timestamp: November 13, 2018, 12:45:11 am
content: Quote from: FriedMule on November 12, 2018, 05:25:13 pmWhat 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.

author: FriedMule
author_rank: Frequent Contributor
timestamp: November 13, 2018, 04:49:45 am
content: Quote from: Richard Crowley on November 13, 2018, 12:45:11 amSorry 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?"

author: Zero999
author_rank: Super Contributor
timestamp: November 13, 2018, 08:46:55 am
content: 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?

author: FriedMule
author_rank: Frequent Contributor
timestamp: November 13, 2018, 09:06:56 am
content: 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.

author: Richard Crowley
author_rank: Super Contributor
timestamp: November 13, 2018, 09:13:34 am
content: Quote from: FriedMule on November 13, 2018, 04:49:45 amSorry, 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.

author: FriedMule
author_rank: Frequent Contributor
timestamp: November 13, 2018, 12:18:40 pm
content: 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. :-)

author: Richard Crowley
author_rank: Super Contributor
timestamp: November 13, 2018, 03:40:58 pm
content: 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.

author: FriedMule
author_rank: Frequent Contributor
timestamp: November 13, 2018, 05:22:02 pm
content: So my reply to him is that it is BULL and even a heap of it:-)

author: bson
author_rank: Unknown
timestamp: November 15, 2018, 08:01:03 am
content: Quote from: FriedMule on November 13, 2018, 05:22:02 pm

author: AndyC_772
author_rank: Super Contributor
timestamp: November 15, 2018, 08:43:28 am
content: Quote from: FriedMule on November 12, 2018, 05:25:13 pmSorry, 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?Quote from: FriedMule on November 13, 2018, 05:22:02 pmI 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.

author: xavier60
author_rank: Super Contributor
timestamp: November 15, 2018, 12:49:46 pm
content: 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.

author: GrahamC
author_rank: Contributor
timestamp: November 15, 2018, 01:13:22 pm
content: 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,

author: Richard Crowley
author_rank: Super Contributor
timestamp: November 15, 2018, 06:30:45 pm
content: You are all ignoring the elephant in the room.The show-stopping problem with this goofy scheme is that THERE IS NOT RETURN PATH FOR THE AUDIO CIRCUIT. In an unbalanced circuit, the shield/screen IS the return path for the circuit. If there is no connection between the source shield/screen/return and the destination shield/screen/return, thenTHERE IS NO CIRCUIT HERE.Telescoping shield is a long-established way of breaking a ground-loop problem between pieces of professional audio gear. But IT ONLY WORKS WITH BALANCED CIRCUITS. Because the balanced pair inside the shield is the COMPLETE CIRCUIT which is INDEPENDENT from the shield/screen.This audiophool scheme takes a perfectly legitimate technique (telescoping shield) and extends it to the absurd point of completely disconnecting the return path by having two disconnected overlapping shields which serves exactly NO useful purpose.

author: helius
author_rank: Super Contributor
timestamp: November 15, 2018, 06:59:27 pm
content: To be precise, the return path is through a lossy, low-quality distributed capacitor.

author: Richard Crowley
author_rank: Super Contributor
timestamp: November 15, 2018, 07:03:19 pm
content: Quote from: helius on November 15, 2018, 06:59:27 pmRight. Which "serves exactly NO useful purpose" at audio frequencies.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: November 15, 2018, 08:19:50 pm
content: If reported correctly there is no return path through the cable. In my mind the jury is out on that. Who knows what the cable actually has in it.The reality is that this will function in a great many systems, since they have a grounded chassis and will get a return through the earth ground. Makes a joke of the shielding, but what did you expect?

author: vk6zgo
author_rank: Super Contributor
timestamp: November 16, 2018, 01:09:00 am
content: Quote from: Richard Crowley on November 15, 2018, 06:30:45 pmNot necessarily, I have seen plenty of unbalanced circuits which use a pair of conductors&a screen.But, of course, this doesn't make your comment invalid.QuoteInterestingly, in my experience, it is fairly unusual in Broadcast work, except for low level circuitry like microphones & pickup cartridges for vinyl record replay equipment.At the higher levels & better S/N ratios of audio reticulated around Studios, it is not necessary.Quote

author: Richard Crowley
author_rank: Super Contributor
timestamp: November 16, 2018, 02:51:28 am
content: Quote from: vk6zgo on November 16, 2018, 01:09:00 amTrue enough. But that is NOT the scheme presented by the OP. Else we wouldn't be still discussing this.QuoteIt is rather a common technique.Refer to the "Bible" of the audio interconnection world, Rane Note 101 "Sound System Interconnection"https://www.rane.com/note110.htmlIn Figure 4. Interconnect chart for locating correct cable assemblies...Note in particular connection diagrams# 1, 2, 5, 6, 7, 8, 11, 12, 13, 14, 17, 18, 23, and 24More than half of the diagrams show telescoping shield schemes where the shield is connected on one end only.As you observed, ALL of them feature a second inside wire which provides the return path for the audio circuit.And the examples here show both balanced AND unbalanced interconnections.In ALL cases where a single-conductor shielded cable is used, the shield is connected on BOTH ends.Note in particular, scheme # 20 which is RCA to RCA.

author: FriedMule
author_rank: Frequent Contributor
timestamp: November 16, 2018, 02:23:37 pm
content: What if you made a outer shield (anode) with no connection at all and a inner shield (cathode) only connected to one unit.In that way, would the outer shield be charged by the RF and EMF from the air and the inner shield would act as the cathode, sinse the charged anode can't dischargeit would get saturated and block for every additional "charge" from the outside?

author: Richard Crowley
author_rank: Super Contributor
timestamp: November 16, 2018, 04:12:26 pm
content: A cable is not a capacitor (except accidentally).A cable is supposed to CONDUCT a signal from one end to the other.In order to have a CIRCUIT, there must be a complete path from the source all the way to the destination.BOTH the inner ("signal") conductor AND the outer ("shield/screen/ground/return") conductor must go all the way through.Again, I urge you to draw out your proposed scheme and show us the signal path including the return.Until you do this, you can throw together any number of fantastic words but they mean nothing.Show us the circuit. Else this conversation has gone on far longer than it deserved.

author: RandallMcRee
author_rank: Frequent Contributor
timestamp: November 16, 2018, 04:13:11 pm
content: I think you all are going off on wild-goose chases. You are just speculating about that cable. The OP has not even given us a schematic. This is the beginner's section. The OP (no offense) seems not to have investigated the actual cable in any detail. We should not be disparaging something without evidence and throwing around wild accusations.That is why my original responses are so brief.Whenever I have investigated these audiophool cables I have usually found solid engineering mixed with exotic materials: the engineering makes it work and the gold/silver/palladium sells it.But now I am speculating!.

author: ebastler
author_rank: Super Contributor
timestamp: November 16, 2018, 04:32:39 pm
content: Quote from: FriedMule on November 13, 2018, 04:49:45 amI think it's clear by now, but just to state it explicitly:The shielding approach which you proposed in your initial post doesnotprovide a gound connection via the outside shield(s). Because each of the shields is connected on one end only, they obviously do not provide a continuous ground connection between the two devices. Hence, this does not work unless there is another, proper ground connection inside the cable.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: November 16, 2018, 05:18:57 pm
content: Just remember, the OP is self identified as limited knowledge and is reporting what an audiophool has told him about something he heard is a wonderful technique. Why would you expect the drawing OP did to have any resemblance to the original cable?Take a low information content source and pass it through two low bandwidth channels and then spend a lot of energy debunking the output. Makes sense to me.

author: coppercone2
author_rank: Super Contributor
timestamp: November 16, 2018, 05:27:39 pm
content: Ok so is it any different then what people to do to fudge usb grounds?How electrically similar is this to having two shielded cables going between two boxes but only connected to one box and connected to the other box by a small capacitor?It kinda sounds like it will resonate. You are linking the grounds through a rudimentary distributed high pass filter. The nondistributed model is cable L and R to set impedance then pass capacitance into a lower impedance since the chassis impedance should be lower then the cable unless its some shady ass glued conductive plastic etc.But its distributed.In my opinion it smells like a last ditch bs hack but idk for sure.By controlling the amount of nesting eg protrusion you set the filter parameter impedance and coupling too.Not sure why to do this. The energy might go through your ground instead.

author: Richard Crowley
author_rank: Super Contributor
timestamp: November 16, 2018, 05:40:43 pm
content: Quote from: coppercone2 on November 16, 2018, 05:27:39 pmUSB uses a balanced, differential data signal pair (D+ and D-)The signal is NOT ground-referenced, so (theoretically) it does not require a ground connection.This is exactly like balanced-pair audio connections shown in my illustration where the cable is "2-conductor shielded cable"QuoteThat is called "telescoping shield" at least in audio circles.It is illustrated in the illustration as # 1, 2, 5, 6, 7, 8, 11, 12, 13, 14, 17, 18, 23, and 24Connecting a small capacitor (active at RF but not audio frequencies) at the unterminated end is also regular practice, especially in conditions where places where RFI is a problem. (Like broadcast transmitter sites, etc.)QuoteNo, it is not any kind of filter. Draw out your proposed circuit with the "filter" and show us.Words mean nothing at this point in the discussion. It is monumental BS.

author: coppercone2
author_rank: Super Contributor
timestamp: November 16, 2018, 05:43:20 pm
content: Your shield impedance depends on the capacitance so its a high pass filter with impedance set by l of the lenght if you imagine it as nondistributed.By shady usb ground i meant when people put like a 5k resistor between usb grounds. This is the same thing but you are putting a freq dep element c rather then r

author: coppercone2
author_rank: Super Contributor
timestamp: November 16, 2018, 05:47:02 pm
content: Untelescope them in your mind till the overlap is almost nothing and you will see it as two inductors connected by a cap

author: janoc
author_rank: Super Contributor
timestamp: November 16, 2018, 06:01:42 pm
content: Quote from: helius on November 15, 2018, 06:59:27 pmNope. At audio frequencies the impedance of such capacitor would be such that it wouldn't have any chances of meaningfully working. The setup would only work if both devices are powered from mains and then the circuit closes through the mains - with all of the wonderful consequences of that, such as hum, noise, distortion, etc.If even one side of the setup would be a battery powered device (let's say a phone having the cable stuck in its phono jack), you would hear zilch.

author: FriedMule
author_rank: Frequent Contributor
timestamp: November 17, 2018, 12:46:58 am
content: I have talked to the audio-addicted and tried to understand what he is talking about.I am not sure about that but I have made a crude drawing.

author: xavier60
author_rank: Super Contributor
timestamp: November 17, 2018, 02:04:53 am
content: Ground loops are not a problem if resulting voltage drops do not become an input noise signal.

author: vk6zgo
author_rank: Super Contributor
timestamp: November 17, 2018, 03:36:44 am
content: Quote from: Richard Crowley on November 16, 2018, 02:51:28 amAt least in Oz, Broadcasting organisations are obviously apostate and don't read your "Bible".Numbers 21 & 22 are the default, with the others used in special circumstances as per my previous post.

author: Richard Crowley
author_rank: Super Contributor
timestamp: November 17, 2018, 05:27:46 am
content: That drawing shows an explicit send and return loop/circuit for the audio (red & blue wires).That is very different than what the OP originally showed us. That is why I kept insisting on a diagram.That is essentially circuit #6, 12, 17, 18 etc.But with an extra telescoping shield from the other end.QuoteVery doubtful. And certainly not worth the expense/effort .Just another exhibit in the museum of audiophool hyperbole.Take some conventional engineering practice and extend it well into absurdity.And then, of course, you can charge ridiculous prices to convince people it is some new magical scheme.Audiophoolery is a cross between cognitive bias and medicine-show snake-oil quackery.Audiophools have NEVER been able to demonstrate objective evidence of any of their claims.

author: FriedMule
author_rank: Frequent Contributor
timestamp: November 17, 2018, 10:11:25 am
content: I have ever only heart one reason for buying expensive cables that I thought made some sense:If you have a great looking system and then put some cheap looking wires on, it looks wrong, therefore nice looking cables to make it all look great. It's like a great turkey made of a great cook and then only add mashed potatoes and ketchup, the turkey doesn't taste the same.

author: Gyro
author_rank: Super Contributor
timestamp: November 17, 2018, 10:36:44 am
content: Iirc, configurations 5/6/11/12 in the above diagrams is where the much maligned and misunderstood 'Directional' audio interconnects came from.I believe they used twisted pair screened on unbalanced RCA jacks, with the screen connected at the source end only.

author: Bud
author_rank: Super Contributor
timestamp: November 17, 2018, 02:19:22 pm
content: Just a general comment that single or double shield effectiveness of a specific cable you can look up in the cable datasheet. A reputable manufacturer specifies it there.

author: FriedMule
author_rank: Frequent Contributor
timestamp: November 17, 2018, 06:00:18 pm
content: Bud, no doubt about that, but now we are talking about a high end cable and not something anyone have ever written any data on, except the marketing on there advertisements:-)