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Servo design subwoofers, what % does the servo use?

Discussion in 'Subwoofers' started by nathan_silly, Apr 6, 2003.

  1. nathan_silly

    nathan_silly
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    I've read somewhere that Servo design subwoofers use a certain amount of amplifier power to reduce THD.

    Does anyone know how much the servo uses? - is that why the HGS servo's have a very high output amp? (is the Paradigm/CHT-15 not enough?)
     
  2. Steve.EX

    Steve.EX
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    Nathan.

    A servo design will to some extent impact on the absolute output (gain) this is not however because the servo is "drawing" on the output stage (as a load)
    I am not aware of ANY U.K owners of Vel, Parad' who have suffered with "it's not enough" (are you mad?)
    If you were to "imagine" max. output comparisons you would only (for the majority) be measuring against a distortion/clip loaded mess in any case.
    For all the tea in china i somehow doubt you would think the Servo 15, CHT15, HGS15, HGS18 underpowered. (oh dear oh dear).


    Steve.
     
  3. Tom Vodhanel

    Tom Vodhanel
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    Hoffman's iron law,

    Somewhere in the 1960s(?) Hoffman (the H in KLH btw) came up with a mathematical formula that became known as Hoffman's Iron Law. Thiele and Small later used this as a basis for the now embraced *thiele/small* parameters of a raw driver. The Iron Law states that the efficiency of a woofer system is directly proportional to its cabinet volume and the cube of its cutoff frequency (the lowest frequency it can usefully reproduce). To reduce the cutoff frequency from 50hz to 25zz you need to increase the enclosure volume by 8x. In other words, to produce half the frequency at the same output level you need a very big box. You can get around this by accepting a much lower efficiency, but this requires both a very large amplifier.

    In other words, if you ran 1 watt into a larger enclosure, you might get 95dBs of clean output at 25hz. But if you ran 1 watt into a much smaller enclosure it might be more like 80dBs. Then you have to factor in the doubling of wattage to raise SPLs 3dBs.

    1w=80
    2w=83
    4w=86
    8w=89
    16w=92
    32w=95

    So it takes 32x the amp power for the tiny cube to produce the same output as the large enclosure in this fictional example.

    Tom V.
    SVS
     
  4. EvilMudge

    EvilMudge
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    Also the Velodyne HGS models use much stiffer suspension on the cone itself, to improve the damping at low frequencies. If anything they are over engineered, whereas the Paradigm Servo-15 is a more elegant solution, though not in the same league of absolute performance. So now you know why they have 1250W amplifiers!:devil:
     
  5. nathan_silly

    nathan_silly
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    Cheers for the info guys, much appreciated.

    What setup would be best?- dual Servo 15's, dual Velodyne CHT-15's, dual CS-Ultra with Crown K1, single HGS-15/18. They're roundabout the same price, give or take a few hundred quid.

    Shame the HGS-18 will be dropped, as I can't fork out the extra for the DD-18- a few hundred quid yes, but not £1000.

    Still looking at dual SVS CS-Ultra's, with a Crown K1. Just need to demo them somehow.
     
  6. deckard

    deckard
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    Nathan

    Multiple subs are supposed to be a pig to set up properly - you can get one cancelling out or adding to the other.

    If you want greater extension and power I'd suggest a single large sub eg HGS-15/18 or a whopping great SVS model + huge amp.
     

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