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Shielded sub cable by the m, how much, where and how to terminate

Discussion in 'Cables & Switches' started by matblack, May 9, 2005.

  1. matblack

    matblack
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    Hi guys

    As per title really, plus I need to know how to terminate this stuff at the faceplates, most importantly how or where the shielding should be terminated

    MB
     
  2. Reiner

    Reiner
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    I assume you are referring to an active sub and a RCA to RCA cable? Then the shielding of the cable should terminate at the RCA connectors outer ring. Once the connector is plugged in, the shield is connected.
     
  3. matblack

    matblack
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    Yep, thats the baby

    Is that what the outer ring does on all RCA cables? Please excuse my ignorance, if this is the case are all RCA cables shielded? With the outer ring purely serving to earth the shielding?

    I'f this is the case then I can just cut up an old sub cable and don't need to buy some special shielded stuff?

    MB
     
  4. Reiner

    Reiner
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    Yep, the outer ring is the shield and typically all RCA cables are shielded (since the cable used for RCA to RCA is coaxial). AFAIK the shield also serves as return path for the signal.

    However, supposingly some cables have the shield terminated at one side only, but if only some of those that claim to be directional.
    I was given the understanding that such a cable is not directional in the sense that it has a direct impact on the signal and thus the sound quality, but instead the fact that it's grounded at one side only will draw any unwanted noise/distortion towards, or away from, the source - can't remember.
    Anyhow, this is what I have been told, I never cut such a cable open to check if it's really only grounded at one side nor have I bothered to check on the idea behind this. Acutally, if I am correct and the shield is also the return path (see above) then I find it unlikely that a directional cable with shield at one end only would work.

    I would think so, i.e. you can use any standard audio interconnect. Only if you have problems with noise introduced a cable with better shield may become necessary.
     
  5. eviljohn2

    eviljohn2
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  6. davehk

    davehk
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    If the shield is connected at one end only, then, since these are NOT balanced interfaces, the signal return must be via some other path - the mains earth wiring is the most likely. Noise voltages on the mains earth will thus be in series with the signal and will be seen across the device's input as part of the signal. Hardly a good idea!

    The idea of connecting only one end of a shield on a singled ended (unbalanced) interface is to prevent earth hum loops. It's not the correct way - it should be done using high quality audio transformers, or by changing (NOT removing) the earthing to stop the loop.

    And, since music signals are bi-directional and any cable should treat a +ve going signal in the same way as a -ve going one (note- their is little or no net flow of electrons in the conductor with an AC signal), then any cable that has directional properties is introducting asymmetric distortion (rectification!). That can't be good either.
     
  7. Reiner

    Reiner
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    I don't think this applies since I was mainly referring to normal RCA cables, which are unbalanced. The question was just if the shield will be connected at both ends or not.

    Agree. In fact it would be impossible if there is no mains earth connected in the first place (hence my doubt that the shield is indeed cut-off).
     

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