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Different speaker cable lengths. OK or not?

Discussion in 'Home Cinema Speakers' started by MarkE19, Jun 12, 2003.

  1. MarkE19

    MarkE19
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    I have setup my speakers with all the fronts with 5m of cable and the rears with 15m.
    With the layout one of the rears only needs a maximum of 5m so......

    Should I keep all the cables for fronts the same and rears the same or does it not matter?
    If they should be the same how should I keep them tidy? I assume coiling the cable is not a good idea.
    If they can be different, how different can they be? Could one be just 2 or 3m and others 15m with no problems?

    In the good old days of plain HiFi I was alway recommended to keep the L/R channels on the same length of cable.

    I am useing Atlas 1 cable.

    Yes it will be nice to tidy all the loose cable, but this is not the reason (well not the main one!). I am about to bi-amp my fronts and would like to get away without spending more on cable (fingers crossed).

    Mark.
     
  2. TheBigApple

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    Although I can see some logic in this theory I don't think it matters to much due to the speed at which signals travel down the cable.
     
  3. Hawklord

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    Same here- my cables are varying lengths on both fronts and rears. Also if your buying higher end cable it can get much more expensive if you buy more than you need. I bought enough with just a bit to spare to try and keep the cost down.
     
  4. sounddog

    sounddog
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    Our cables are equal length Left and Right ... then the surrounds are both same length, and the centre backs are both the same length. Really for no other reason than they're convinient.

    Vikki
     
  5. MartinImber

    MartinImber
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    Same here - same length but because I may move something.

    2.5m on each front
     
  6. Ian J

    Ian J
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    There are scientific theories why the speaker cables should all be the same length but I am not sure whether it is noticeable in the real world on equipment in this price range.
     
  7. NicolasB

    NicolasB
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    I am officially no longer a newbie on this forum and have become an embittered "oldbie". I can say this with confidence because I've got to the point of being annoyed by people who don't do searches before posting questions that have been answered before. :mad:

    Mark, I suggest you click here.
     
  8. MikeK

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    As well as signal attenuation, another effect of the speaker cable's impedance is on the amplifier's damping factor - that is it's ability to control cone movement (or more accurately, deal with the back emf created by the driver voice coil, which in turn affects it's ability to control the cone).

    Given that it's commonly thought that factors above 20-30 are sufficient (and that there is little/no real world advantage above this), you have some amount of leeway before it might become an issue.

    The damping factor is basically the load impedance/source impedance. So, for an 8ohm nom. speaker, and an amp with a 0.1ohm output impedance, the damping factor is 80, which is fine. However, now add 0.4ohms of speaker cable impedance to the amp's output impedance, and it drops to 16.
    Of course, other factors come into play as well (not least, the crossover circuit inside the speaker cabinet), making the above a crude calculation, but it illustrates the point.

    Now, it's a bit more complex than that - that 8ohm speaker is unlikely to be 8ohms at lower freqs (the freqs where the biggest back emf most likely occurs), more like 5ohms. Doing the math again, that makes the DF 50 without cable, and only 10 with a 0.4ohm cable.
    (this is assuming that the amp's output impedance is constant as well), so in this case using a lower impedance cable may be in order - doubling it's thickness will bring the DF back up to 20, as would halving it's length. Do both, and the DF will be up to 40.

    Of course, the above really refers to a single driver attached directly to the amp. In reality, few "speakers" we use are like that - they are a combination of bass/mid and tweeter seperated by a crossover, which complicates matters further.



    Now, what about equal length cables?
    Well, if you use one length of 0.1 ohm cable and another of 0.4ohm (ie 4x as long), then you'll end up with a DF on one channel of 25, with a DF on the other of 10.

    Will that sound different?
    No way to say for sure, but it's possible - so making the cables of equal or similar length will eliminate the possibility of this causing an audible difference, and as it's easy to do, and doesn't cost much (unless you are a believer in exotic and expensive speaker wire, which I'm not), then it's difficult to argue a case against (IMO of course).


    Personally I wouldn't argue that cables should be absolutely identical in length, but IMO they should be similar.
    I often wonder whether it's this effect at work when some people hear a clear difference between some speaker cables on their kit, and others don't on their's (apart from the rather more obvious placebo effect :) )

    Bottom line - IMO, for speaker cable, equal or similar lengths , reasonably thick (12AWG for instance), no longer than necessary!
    The longer the cables, the thicker it should be (but still keeping things sensible - there's usually no need for a copper crowbar :) ).
     
  9. Bernard Barnett

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    If you do go for similar lengths (and I agree that there's no necessity unless you're talking about very long cable runs), it's more important not to coil up any excess - now that would degrade the sound.
     
  10. wookie

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    Coiled cable is an inductor.
    Cable should be folded concertina style.
     
  11. NicolasB

    NicolasB
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    To produce an impedance of 0.4 ohms an (uncoiled) speaker cable would have to be something like 40m long.
     
  12. seany

    seany
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    What is worse is when you extend cable like i have, it was a short tearm fix but i've left it for ages now.
     
  13. MarkE19

    MarkE19
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    OK, thanks for the replies.
    When my new amps arrive I will have a play with positions etc. and try and keep the lengths at least similar, but not coiled.

    I do intend to keep some spare length on the cables just in case I do move things around again, but hopefully not too much.

    Mark.
     
  14. NicolasB

    NicolasB
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    I suspect most of us would agree that not coiling the cables is more important than having them the same length. Having a lot of stray inductance about the place will create all kinds of problems.
     
  15. sinister_stu

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    I was going to say that after reading MikeK's post. Whilst there are lots of interesting points in his post, this assumption for cable impedence is too crude. Its more likely that the longer cable would have an impedence of 0.1 ohms and the shorter one being a fraction of that. This would mean that change in the damping factor would be of no consequence.

    Differing cable lengths, unless extreme, will not make any difference. I remember reading on another forum that the distance you are from each of the speakers has more effect on the sound than cable lengths... and this isn't an audible effect.
     
  16. NicolasB

    NicolasB
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    The point about speaker distance was probably made by someone who wanted to compare the effect of speaker distance to the effect of cable length in terms of the timing of the signal. That really is almost unmeasurably small. But impedance issues could be significant in extreme cases.

    Aside from anything else, if you've got a cable with an impedance of 0.4 ohms and a choosy speaker like a B&W Nautilus 803 (whose impedance varies from 8 ohms down to 3.0) then the fraction of the total impedance of speaker+cable that the speaker accounts for will vary between 88% and 95%, which would be enough to produce an audible effect on the speaker's frequency spectrum. At signal frequencies that coincide with the speaker's lowest impedance values the speakers will produce relatively less volume than they will at high-impedance frequencies, because more of the signal will be being dissipated by the cable. This is why B&W recommend that you keep your speaker cable impedance to 0.1 ohms or below.

    Similarly, if one cable had an impedance of 0.1 ohms and the other 0.4 ohms, then the speaker-impedance-fraction figures would be 88-95% on one side and 96.8-98.8% on the other, so in that case not only would one speaker be slightly quieter, but you would probably also just about about be able to hear a tonal difference as well. But if you compare 0.1 ohm figures with 0.05 ohms, that's 96.8-98.8% on one side and 98.3-99.3% on the other. I don't think that would be audible, and there you're talking about one wire being 5 metres long and the other one 10 metres, hardly a tiny difference.
     
  17. MikeK

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    Don't forget that a typical speaker cable is actually 2 wires not one! :)

    In any case, the figures were simply for illustration purposes.

    There's plenty of info available on the web about this - I suppose NicolasB will like this one best

    http://www.bryston.ca/newsletters/54_files/vol5is4.html

    :)
     
  18. sinister_stu

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    Fair enough, just wanted to make sure that others realised too. Don't reckon that there are many too people who have had problems with cable lengths having adverse effects on the damping factor.
     
  19. MikeK

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    Don't reckon that there are many too people who have had problems with cable lengths having adverse effects on the damping factor.

    Stu

    That's the issue though - how do you know?

    It's not as if the system won't work or anything, and the effect could range from very subtle or non-existant to quite audible.

    The only way to tell really would be to replace existing cables with much thicker and shorter ones - then see if there's any appreciable difference in sound quality. If there's not, then fair enough, the system in question probably had no issues in this respect - but what if there is?..........
     

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