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  1. #1
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    Speaker Wire, Shielded Versus Unshielded?

    Can someone give a lucid understandable reason(s) for the advice never to use shielded [wire wrapped] wire to connect speakers. The reason I ask is that some friends hooked two commercial Cerwin-Vega speakers to a Peavey mixer using shielded [intended for usage with XLR connections] despite directions in the Peavey Manuel plus my advice NOT to use shielded wire for speaker connections. Their reasoning was that they had plenty of shielded wire and saw no reason that it would not serve the purpose. I do not have enough technical knowledge to really explain why it should not be used. Such statements as "might burn out the amplifier" do not really explain why that would happen [there is a 400 watt amplifier in the Peavey mixer]. Help me out if you can. By the way, the speaker jacks (1/4" stereo) are located 30 to 40 feet from the mixer.
    GeneK
    Last edited by GeneK; 21st Nov 2005 at 16:17. Reason: Add information.

  2. #2
    Senior Member SC358's Avatar
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    Re: Speaker Wire, Shielded Versus Unshielded?

    Electronically the speaker circuitry is floating and does not require any chassis or earth ground. Shielded cable can be used (whether to save monetarily or no extra cables, etc... etc...). The two wires would attach to the speakers but the shield should NEVER be connected in any manner - it should be cut back completely and unexposed. IF there is some sort of breakdown in the insulation jacket of one of the wires and even a strand of wire touches the exposed shield, that short circuit will blow the amplifier .

    If the speaker cable just lays around and is never touched there shouldn't really be any problem. If the cable is constantly getting attached/deattched, then there's potentional for a cable shorting due to wear and tear.

    Speaker wire can take a beating and there is no risk of a short.

    I hope I was lucid enough...whew....
    SC358
    Relationships are based on compromises - behavior accepted is behavior repeated.

  3. #3
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    Re: Speaker Wire, Shielded Versus Unshielded?

    Shielded vs. Unsheilded is not the thing to worry about, it is the gauge of the wire. In your case, you should be using a minimu of 12 gauge wire. I would venture a bet that if the cable you are using was meant to be used for XLR connections, it most likely is not 12 gauge. Just double check. If you need further explaination on different gauges of wire and why it is important, just ask and I would be happy to give you short tutorial.

  4. #4
    Senior Member SC358's Avatar
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    Re: Speaker Wire, Shielded Versus Unshielded?

    I agree with Rrybaker, the main concern of speaker wire is the gauge. But just like everything in life there are consequences & rewards for things done properly and the short cuts we take - you must choose...WISELY .
    SC358
    Relationships are based on compromises - behavior accepted is behavior repeated.

  5. #5
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    Re: Speaker Wire, Shielded Versus Unshielded?

    Quote
    Quote: SC358
    Electronically the speaker circuitry is floating and does not require any chassis or earth ground. Shielded cable can be used (whether to save monetarily or no extra cables, etc... etc...). The two wires would attach to the speakers but the shield should NEVER be connected in any manner - it should be cut back completely and unexposed. IF there is some sort of breakdown in the insulation jacket of one of the wires and even a strand of wire touches the exposed shield, that short circuit will blow the amplifier .

    If the speaker cable just lays around and is never touched there shouldn't really be any problem. If the cable is constantly getting attached/deattched, then there's potentional for a cable shorting due to wear and tear.

    Speaker wire can take a beating and there is no risk of a short.

    I hope I was lucid enough...whew....
    Very Clear [lucid] and understandable. If sound is transmitted as an AC current [as I have previously read somewhere], very unique in that that no grounding is required. Thank you so much [sorry I am so late with that].
    Gene

  6. #6
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    Re: Speaker Wire, Shielded Versus Unshielded?

    Quote
    Quote: Rrybaker
    Shielded vs. Unsheilded is not the thing to worry about, it is the gauge of the wire. In your case, you should be using a minimu of 12 gauge wire. I would venture a bet that if the cable you are using was meant to be used for XLR connections, it most likely is not 12 gauge. Just double check. If you need further explaination on different gauges of wire and why it is important, just ask and I would be happy to give you short tutorial.
    I am ready for that tutorial, please sir. I have not yet [busy time of year] checked the size of that XLR wire, but I am guessing at no bigger than 16 or 18 wire gage.
    Gene

  7. #7
    Quote
    Quote: SC358
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    Electronically the speaker circuitry is floating and does not require any chassis or earth ground.
    Does this mean that the audio signal being transmitted along the speaker wire is not affected power sources and other nearby electronic devices?

    I ask, because the primary reason I would think to use shielded speaker wire, would be to protect it from external interference.

    I am currently dealing with a cabling problem within a large gymnasium that seems to be affected by the A/C system and other electronic sources. I was looking into options such as shielded speaker cabling as a solution. Would it be pointless?

    Please clarify.

    Thanks,
    A/V Newbie.

  8. #8
    The reason shielded speaker wire should not be used is that it can destroy the amplifier. Reason enough?

    All speaker cable has capacitance; it's unavoidable. With unshielded cable, you only have the capacitance between wires. With shielded cable, you have the additional capacitance between each wire and the shield. Thus shielded cable has much greater capacitance.

    Capacitance attached to an amplifier output acts as a drag on the signal. It's like a Leyden jar that the amp has to charge, discharge, reverse charge and discharge again with every cycle. In extreme cases, this drag can cause such a phase shift at very high frequencies that the amp goes into oscillation. Usually the oscillation is at such a high frequency you can't hear it, so you don't know anything is wrong (other than excessive distortion) until after the amp and speakers have burned out.

    Worse, an oscillating amp pushes itself into overload. Thus a 400W amp becomes an 800W oscillator.

    Audiophiles get away with using shielded cable in their home stereos because the runs are only 8-10 feet. You, however, with much longer runs, are asking for trouble.

    What I've said so far is common industry knowledge. What follows is personal opinion. This goes beyond your original question, but I never pass up an opportunity to bash shielded speaker cable.

    1) The whole shielded speaker cable industry is a fraud. It is a mental disease, an infection caught from certain tweaky high-end audiophiles who think snake oil is better than science. The best that can be said for shielded speaker cable is that, with the short 8-10 foot runs typical of home stereo systems, it doesn't do much damage.

    2) A shield that is not connected to chassis ground doesn't even shield. A high percentage of expensive audiophile shielded cables have no grounding option, which is a dead giveaway that the cable maker doesn't understand the science.

    3) A cable shield only works against electrostatic interference, which is a relatively high-impedance phenomenon that usually doesn't affect speaker lines because of their low impedance. Most of the interference sources that actually might pose a problem, like light dimmers, radiate magnetic interference. Cable shielding is useless against magnetic interference.

    4) The best interference protection is the use of balanced lines. From a magnetic standpoint, all speaker lines are automatically balanced, unless somebody has earth-grounded the line at the speaker end.

    5) If speaker wiring needs to be shielded, what can you say about the 80 years between about 1920 and 2000 when nobody did it?

    In short, shielded speaker cable is a precaution that doesn't work against a problem that doesn't exist, has never been necessary in the past, does not improve the sound, endangers the equipment, and costs extra money.
    Last edited by karl eilers; 13th Oct 2009 at 17:08.

  9. #9
    hulettk - specific answers to your questions.

    I would never say interference sources cannot affect speaker lines - only that shielding is unlikely to do anything to improve the situation.

    If you're having interference problems, you need to pinpoint where it's coming in. It is likely that the interference is coming into the system from somewhere else besides the speaker lines, simply because the signal on those other lines is thousands of times weaker and thus more easily interfered with. Try unplugging the input to the amp (or, if it's an mixer/amp, all the inputs). The only things that should remain connected are the speaker line and the AC power. Does the interference still occur?

    If you do still have problems, try plugging the amp in thru an AC power filter. We're trying to eliminate all other possible noise sources besides the speaker line.

    Suppose you still have noise, and we've determined that it can only be coming in on the speaker lines because we've eliminated all other possibilities. Your best weapons are 1) balanced wiring and 2) distance.

    The best speaker wiring, from the standpoint of interference immunity, is an unshielded twisted pair. Run it at least a foot away from all AC power lines if you can. Where it must cross a power line, cross at right angles - this cancels any magnetic coupling. Don't let the speaker wires get anywhere near a dimmer bank or light bar.

    (Speaking of AC power lines, in a school I would assume all permanent AC wiring is in conduit. Thus it already has an electrostatic shield.)

    Do not ground either side of the speaker line at the speaker. At the amp, you may have no choice. To clarify what SC358 said, an amplifier with an 8-ohm output is not floating and usually not balanced, and you have no choice about grounding at the amp end - but grounding at the amp end isn't as bad as at the speaker end.

    However, in a large gym, you may well be dealing with a 70-volt system, in which case the speaker line is floating (not connected to any earth ground), and lucky for you, because that's the best of all possible situations.

    If you use unshielded twisted-pair wiring, keep it away from AC circuits, and don't ground it at the speaker - and ideally, if it's a floating 70V system - it should be immune to anything an A/C system or other equipment can throw at it.

    There may be one other problem: radio-frequency interference from radio/TV stations, CB, police/fire communications, or your own wireless intercom if you use one. That's a whole 'nother can of worms, but this post is long enough already. Try what I suggested and report back.

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