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Shielding

Discussion in 'AV Receivers & Amplifiers' started by KornChild, May 3, 2005.

  1. KornChild

    KornChild
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    Forgive me if this has been covered or is in the wrong area. This is my first day on the forums after trying some research online and deciding I need to speak with someone about my questions.

    I own a Yamaha RX-V640 & plan on using it to try and make as close to a professional home theater room as I can. I will upgrade in the future but for now here are my questions.

    I work at a Best Buy here in the U.S. in the computer department but have a basic understanding of home audio/video. I recently had a customer come in who I had to help out over in home theater and he was talking about running his cabling for his 6.1 system. He said he had gone to a hardware store and purchased long peices of copper pipping that he was going to run his audio cables through as shielding against power lines and RF. Now my question is what is the best material to even shield further your cables/equipment, is copper pipping like stated above a good idea for cables etc? What might be a better material or better idea?

    Thanks for all the input I greatly appreciate it!
     
  2. Harry T2

    Harry T2
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    Probably the wrong forum, but I will add my 2c worth.

    Copper would be close to the “worst” material I could think of for dielectric insulation. Much better are other materials at the other end of the spectrum like plastics, nylon and air.

    I personally wouldn’t worry too much the effect on speaker cables runs, but depending on the size of the solenoid in the electrical equipment insulation may be justified. Again distance between the 2 items is best.
     
  3. KornChild

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    Thanks for the input, can you maybe take it down a notch to kindergarten terms for me. Why did this old guy come in claiming to be some audio expert and run his wire through copper etc? My monster cable speaker wire has noticable static when turned up with no audio and it is running across all sorts of power cords, computer, power strip, etc etc. What would be a good way of adding to the obviously little filtering that monster cable provides?
     
  4. Harry T2

    Harry T2
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    I wouldn’t even attempt to guess what he was thinking.

    Are you saying that when you select an input on the amp that has no component connected to it, you hear the static?

    If it is, then this is a common characteristic of amps. It want be noticeable when the amp is in use and connected to a component. If it is an issue for you still, then you need to “short” the inputs that are not in use at the back of the amp.

    I would “tidy” up the other runs of cables as I don’t think this will be causing much of what you are hearing. Having said that, I would still try and keep cables from touching each other (as much as is practical), and where cables must cross, cross on the perpendicular (ie 90 degree angle, and again, as much as practical).
     
  5. KornChild

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    Sorry I wasn't very clear at all. Right now I live in a tiny room, but when I move I am planning to do this all the right way the first time. What I ment by hearing static was this.

    I switched my receiver to an input that had nothing connected to it and turned it all the way up to 0db to be exact and barely herd static. I switched the input back to what I have my xbox on running optical audio input with the xbox sitting in a menu with no audio coming through I turned it all the way up to 0db just like before and herd 10x as much static as before. Now I assume that is what is being picked up in my speaker cable being run through my room due to how it is having to all be ran in a small place with so much equipment.
     
  6. Harry T2

    Harry T2
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    It is definitely static and not a hum at a constant frequency?
     
  7. KornChild

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    Alright well I just double checked and here is what I found.
    My yamaha has all sorts of different inputs just like any other receiver/amp.

    VCR2/DVR (running xbox optically) | Digital , CinemaDSP
    vcr1 (picks up barely any static at all the way up) | Has nothing.
    v-aux (empty) | PL, CinemaDSP
    dtv/cbl(empty) | PCM, Pl, CinemaDSP
    dvd(empty) | PL, CinemaDSP
    MD/cd-r(empty) | HiFi DSP
    cd(empty) | PL II

    With my xbox on and running sitting in a menu like I said above with no audio coming through (because I am in menu and not in game) has quite a bit of fuzz coming through at 0db, the rest of the inputs except vcr1 have close to just as much static coming through but maybe at a different tone..?

    Hope I gave enough information, thanks for bearing with me since I'm all noob : )
     
  8. Harry T2

    Harry T2
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    OK, lets remove the speaker cable from the scenario (as I am beginning to suspect you have a “ground loop”/earthing issue as the static will be across all inputs).

    As a cheap experiment, get some polystyrene cups and raise the speaker cable up of the floor onto the cup (inverted is a little more stable, but it doesn’t matter) for the entire distance of the run. Making sure that it is not in contact with anything other than the connection at the ends and the cups. Or you could disconnect the speaker cable from the amp and use some headphones.

    Once the above is done, I would expect to hear NO CHANGE in your system, and thus conclude it is not the speaker cable.

    I know it is a lot of work to achieve nothing, but we need to eliminate possibilities to determine what the error may be, and hence some diagnostic work is required
     
  9. KornChild

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    Alright well I plugged in my head phones and went through all the inputs on my receiver, all had about the same level of static coming through except the VCR1 input. They all had roughly the same volume and a very very slight highpitch whine when you switched channels, probably nothing however.

    When run through my speakers the static isnt noticable unless I have the volume half way up or more which is insane loud anyways. And when audio is coming through the speakers the static isnt very noticable at all. I just want to get as close to perfect as I can which ideally would be like input VCR1 pretty much seing as how I barely hear anything at full volume for some reason.
     
  10. KornChild

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    Bare with me here if this is stupid maybe I didn't clarify before or I'm not understanding.
    This I got off monstercables website:
    "Why use braided copper and foil shielding?
    Braided copper has been proven to the most effective way to repel RFI(radio frequency interference). Foil shielding is the most effective way to shield against EMI(electro- magnetic interference). "

    So why would running my speaker cable through copper pipping be a bad idea? And why would you say copper would be your idea of the worst material?
     
  11. chedmaster

    chedmaster
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    the xbox is not a piece of home cinema engineering and was never designed to be run at 0db, if i were you just live with the static if you ever turn the xbox up that high! Optical cables surely can't pick up static, so it must be the xbox's electrical circuits causing this. i know its nice to feel you have a "static" free system, but if it doesn't effect your gameplay then whats the problem.
     
  12. chedmaster

    chedmaster
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    it could also be the display in your amp, the brighter the display on my old amp, the more hum i heard during silence (inaudible unless right next to the speaker). Try dimming/turning off the display.
     
  13. KornChild

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    Thanks for the tips ched, but like in this post above, the static is similiar to the other inputs except vcr1. So I'm thinking its not the xbox and I do realize that its not anything near........ nice equipment. But I plan on upgrading also like stated above so if it isn't a problem with the box then I'd like to get started on figuring out what it is. Appreciate the help guys!
     
  14. eviljohn2

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    In reality the guy in the shop with the copper piping may actually have been onto something. If the pipe were connected to earth, no electric field would be able to propagate into or out of the piping (a search on Gauss' Law should turn up some theory supporting this for those that are interested). Even if the piping wasn't connected to electrical ground, if it was thick enough it may help to attenuate very high frequency noise incident on the cabling although using a ferrite clamp at one end of the cable would probably have a more noticeable effect. :)
     
  15. Harry T2

    Harry T2
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    It is not a stupid question. And I probably don't have the answer, and equally dismissed it without to much thought. I would add that braided copper is not copper piping, and and foil shielding is not copper piping.

    I will need to think about this, and remember some of my Uni Physics. Yes, EvilJohn, Gauss' law wil have something to do with it, but I will think the dielectric issues maybe more significant.

    Getting back to the initial hum, does it sound the same with the computer & moniter turned on and off.
     
  16. eviljohn2

    eviljohn2
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    Harry and Kornchild, any grounded metallic conductor surrounding the cabling (including pipe, braiding or foil) would act as an effective EM shield. The problems it would induce would probably be to do with increased capacitance and is one of the main flaws in the "semi-balanced" interconnect design.

    Overall, I think that if you have such a high level of noise that such shielding would be necessary then time would be better spent reducing the noise at source rather than stopping it reaching the cabling. :)
     
  17. Harry T2

    Harry T2
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    I must admit that I had confused myself with shielding and insulation.

    Agree, Eviljohn. It would be much better to shield the source. Afterall, many high-end products to use a copper casing for that very reason.
     
  18. KornChild

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    Copper casing or copper pipe..... same thing in the end right? Why not do that to your cables if your receiver case is the same thing?

    Pretty much the general answer has been best just to get alot of wire and turn it into twisted pair with a drill or somethin and leave it at that. However I had originally planned on building a stand/cabinet type encloser for my receiver with the inside plated in copper and then run copper pipping out the back and run my wires through that etc. Sounds like alot of work and time but just a thought at the moment to see what everyone thinks etc...
     
  19. KornChild

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    What problems would it induce? Sorry, if you could take it down a notch for me and kinda spell things out I would get a much better understanding lol.

    So do you recommend any type of additionaly shielding? If so what do you suggest that I can get?
     
  20. eviljohn2

    eviljohn2
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    Kornchild,
    The Beekeeper outlines the problems very well in this post:
    http://www.avforums.com/forums/showthread.php?t=122271&highlight=semi+balanced

    I can't really recommend any additional shielding - if it's necessary then the cables aren't really up to the job in the environment you're using them in. This is very unlikely to be the case in a home environment without any electricity pylons in the room.l One thing you could try is getting some ferrite clamps and putting them around the cables at the component end of the wire. :)
     
  21. Harry T2

    Harry T2
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    That was one very good post by The Beekeeper.

    Thanks for that EvilJohn
     
  22. KornChild

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    Thanks for the link! I'll be reading over it shortly, sorry for the annoyance but..... ferrite clamps? What are the advantages of these and where can I find them? Component end being the receiver....? Thx
     
  23. sillybeans

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    Ferrite clamps - I think they are basically round magnets with a whole through, usually split in half and then "clamped" within plastic casing around a cable.

    I had a big problem with a 10m cable to my sub that hummed when it had no input. I used a couple of these magnets salvaged from an old Omron till and the hum dissapeared completely. I was pretty amazed at how effective it was.

    Don't know if it works better on coax cable than speaker cable though!

    Mike
     
  24. KornChild

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    Did this to give you guys a better idea of the equipment I'm using. Everything connects to the receivers via banna clips that are screwed on to the ends of the Z series cable, and for the normal cable below that I have clamps that are screwed down onto the cable.

    http://www.monstercable.com/productPage.asp?pin=912
    Monster Cable Interlink® LightSpeed™ 200 Higher Performance Digital Fiber Optic Cable | Ran from computer to receiver and from xbox to receiver


    http://www.monstercable.com/productPage.asp?pin=37
    Monster Cable Z1R Z Series Cable | Current Front left and right speaker cable

    http://www.monstercable.com/productPage.asp?pin=48
    Monster XP® Clear Jacket - Compact Speaker Cable | Ran from receiver to rear speakers
     

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