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Is This A Bargain For Surround Cable?

Discussion in 'Home Cinema Speakers' started by nickyvicar, Apr 30, 2003.

  1. nickyvicar

    nickyvicar
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  2. MikeK

    MikeK
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    It may be a bit thin for long runs IMO.

    The longer a speaker cable is, the thicker it really needs to be, within reason of course.

    If you use a cable which is too long and thin, the damping factor of the amplifier is affected to a much larger degree.
    Opinion differs as to what the acceptable minimum damping factor should be, but keeping it above 40-50 seems to cover most eventualities.

    The damping factor is the load impedance / lumped source impedances of the driving source (which means the source (ie output) impedance of the amp, and the impedance of the speaker cable)
    Consider an average amp with an output impedance of 0.1ohm and a load impedance of 8ohms (nominal). Damping factor is 8/0.1 = 80, which looks fine. Now add a run of cable, say 10m (which in reality is actually 20m - there's two pieces of wire) which has a resistance of 0.4ohms. Damping factor is now reduced to 8/0.5 = 16. If the load were 4ohms, damping factor would now be 8, which is really getting too low.
    (this is ignoring any inductance and capacitance effects of the cable)

    If the cable were thicker, and the resistance was reduced to 0.1 ohms, the damping factor would now be 40.

    So, to obtain a damping factor of 40, the cable can be up to 0.1ohms.
    This means either 2.5m of the thin cable, or 10m of the second thicker cable!


    This is a possible explanation of the dramatic improvements in sound they got back in the 70's when they switched from their coils of bell wire to 30A mains cable - and so an entire industry was born :) :)
     

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