DIY cable lengths- how to make cable sets same length and must they be exact?

Discussion in 'Archived Threads 2001-2004' started by Judy Y, Aug 8, 2002.

  1. Judy Y

    Judy Y Stunt Coordinator

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    Is there a trick to making cables exactly the same length? With rolls of stiff RG 6 I am having a problem measuring and getting the cable sets the same exact length, (cable keeps twisting and curling). How important is this??????? How far off can one be and not cause a problem???? Does it make a difference with audio verses video cables....... like component video cables? What about SACD or DVD-audio 6 channel cables?
     
  2. Bill_Weinreich

    Bill_Weinreich Second Unit

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    Purists would say it could cause a problem but because electrical signals travel at the speed of light (186k/m/s), there shouldn't be any discernible difference.

    Bill
     
  3. I just measure them one at a time stretched out over a tape measure
    with the speed of light at 299,792,458 m/s
    ...and my possible 1/4" off, I can live with the sound propigation error of 21 pico seconds.
    I got a million dollars for the "audiophile" that can here that difference[​IMG]
     
  4. Bill_Weinreich

    Bill_Weinreich Second Unit

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  6. Bill_Weinreich

    Bill_Weinreich Second Unit

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    I agree Anthony [​IMG]
    Judy,
    If you are concerned about keeping the same length, after you cut the first piece, tape the next one to it every 6" or so and cut the next length.
    Bill
     
  7. Judy Y

    Judy Y Stunt Coordinator

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    Good idea, Bill. Thanks, guys, for your replies. I am not concerned, just wondered if it made any difference.

    What, no "purists" answered? Not even for a million dollars?
     
  8. it was because each of my bills were not perfectly exact. Because of the lack of exactness, it might mess up the audio Karma in their custom designed and acoustically invisible, listening chair.
     
  9. Phil A

    Phil A Producer

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    I'm a purist - component video should be kept as close as possible to the same length, within a couple of inches. If you are talking normal lengths of audio cables a couple of feet should not make a difference that one can hear although there could be measured electrical differences. Close is fine for audio cables and hand grenades. If it makes you feel better I could come over and put a seal of approval on it. I did make my left and right speaker cables the same length but the center is a couple of feet shorter. I trust you will not tell anyone.
     
  10. Saurav

    Saurav Cinematographer

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    A minor technicality - light propagates in a physical medium much slower than it does in vacuum, so the electric field would actually only be moving at around 50% the speed of light.

    But, that's completely irrelevant. Cable length has nothing to do with the speed at which light propagates. You could have two cables with a difference in length of a few miles, and it still wouldn't make a significant difference to the time taken for the signal to propagate through the cable. However, the resistance and capacitance of the longer cable would be much higher than the shorter cable, so you'd get frequency response problems. You'd still get the signal there within picoseconds of each other, but one signal would be missing a lot of high frequency information.

    Would I be able to hear a difference between two cables which differ in length by a mile? Definitely. Would this difference have anything to do with the speed of light and delayed signal arrival? Absolutely not.

    So, to sum it up - you're right, electric fields move through copper very very fast, and that fact is totally irrelevant.

    Anyway. Judy, to answer your question - I don't know about video cables. For audio interconnects, I wouldn't make them too much different in length, try to keep them within a couple of inches of each other, I guess. Speaker cables are different, the impedances are different and length isn't that much of an issue. Not so with interconnects and preamp/amp impedances. Depending on the amp and the cable involved, a difference of a foot could change the cutoff frequency by several kilohertz.
     
  11. Saurav

    Saurav Cinematographer

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    Because that's not complicated enough [​IMG]
    Seriously... an inch or so difference, I really don't see how that could matter. 6' on one side and 9' on the other side - that could very easily be audible. That's all I was trying to say. Some people like to keep monoblock amps close to the speakers, so they might end up with the preamp being closer to one amp than the other.
     

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