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Bending optical [toslink] cable

Discussion in 'Accessories, Cables, and Remotes' started by seth_petry_john, Sep 15, 2004.

  1. seth_petry_john

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    When I first hooked up my equipment, which uses two different Toslink optical audio cables, I looped them back and forth and then zip-tied them together for a neat appearance.

    I've since learned that bending the optical cable is usually a bad thing because it can reduce performance.

    My two questions are:

    1) How much of a performance issue should I expect from a bent cable? Would it be an "all or nothing" issue, i.e. if the bent is too great there would be no sound at all, or would the sound signal just be degraded in some way?

    2) Having zip-tied the cables in a rather tight bend, and having left them there for over a year, should I expect there to be permanent damage to the cable?

    I've been living in a cramped space for the past year, and my entire setup is in severe need of calibration and relocation. I don't really have any other experience with this gear to determine for myself if sound quality is suffering from the cable bends or not.

    Thanks in advance,
    Seth
     
  2. Max Leung

    Max Leung Producer

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    Never bend optical cables. It would screw up the optical path the signal travels through. Think of the curvature of a camera lens, and you'll realize why bending optical cables (too much) is a bad idea.

    Optical cables can be looped to a degree...sometimes the cable manufacturer will label the smallest circumference you can use, but most do not.
     
  3. Chu Gai

    Chu Gai Lead Actor

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    All fiber optic cables have a spec associated with them called the bend radius. This is the maximum bend (look at it as bending a cable around a coin) the manufacturer recommends before reflections lead to an unacceptable signal loss. The smaller the fibers, the tighter you can bend the cable. If the spec isn't listed, I'd figure on something like 3/4 to an inch as the radius. Now, unless you've actually broken the fibers, which could lead to dropouts, the good news is that its reversible. So, uncoil those cables, and if you have to coil them, just make sure its not smaller than the values I mentioned above.
     
  4. Leo Kerr

    Leo Kerr Screenwriter

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    But, I think in your situation, leaving them 'as-is' may not really hurt anything. In fact, it's possible that unbending them may cause them to break.

    Now we get into the smoke and mirrors and religion.

    Is the signal being degraded? The short answer is, yes.

    How? Most likely by reducing the signal-noise ratio, because more light is getting lost in those bends.

    Is it hurting the data?

    Very likely not. Digital does tend to be an all-or-nothing system. In your situation, what may be happening is that your.. 1.5 meter cable (you didn't say, I'm guessing,) may now appear to the system as, say, a 15 meter cable... without the benefits of a 15m cable.

    Leo Kerr
     
  5. seth_petry_john

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    So I guess the best thing to do is wait until I get the gear situated, and then order cables as close to the actual length I need as possible so that I can still maintain control over the rats nest without bending the cables too much.

    Seth
     
  6. Chu Gai

    Chu Gai Lead Actor

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    Hell, I'd just reuse them.
     
  7. Ted Lee

    Ted Lee Lead Actor

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    i didn't think s/n ratio was an issue in an optical path?

    how does that work? seems to me (like you mentioned) that's it's still digital. on or off??? so how would less light equal worse s/n?

    just curious...
     
  8. ChristopherDAC

    ChristopherDAC Producer

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    that's signal-to-noise, in the analog [mtf] domain, from the optical transmitter [laser diode] to the optical reciever [photodiode]. too much noise, and the device which is interpreting the analog signal [modulated light] "gets lost" and starts putting out faulty strings of 0s and 1s, or cuts out altogether. this has absolutely nothing to do with the s/n ratio of the digital signal traveling by way of the analog transmission channel unless and until dropout occurs; it is analogous to radio-frequency interference on a coax digital cable in that way.
     
  9. Ted Lee

    Ted Lee Lead Actor

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    oh..i get it now. thx dac!
     

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