Sub advice

Discussion in 'Subwoofers' started by Maki, May 3, 2004.

  1. Maki

    Maki
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    I am thinking of buying a sub, but need a little advice first. I currently have as main speakers Kef Q55's, which do have great bass response. So that said, I need a sub that can underpin these speakers.
    My room size is also a consideration being 22'x12', quite a large room, so a sub to match this also. I do not want to make a mistake here and buy something that has little effect, so good advice is what I am after. As a starter I have been thinking of the B&W 675 or MJ ref1.
    Music is as important as movies so a good all rounder would be nice!
     
  2. Nimby

    Nimby
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    Maki

    What's the claimed bass roll-off (-3dB) point of the Q55s?

    Nimby
     
  3. russraff

    russraff
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    Q55's have a claimed 40Hz freq. response. I reckon that this may be a little optomistic, though. When I demoed a pair, my REL Storm, at the time, worked best at ~55Hz (can't remember the figure exactly).

    Kef q55

    Russell
     
  4. Nimby

    Nimby
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    Russell

    There doesn't seem to be a direct correlation between speaker roll-off and the sub's cut-off setting. My 753Fs are 40Hz but my sub is set to 60Hz for a flat response. Set to 40Hz there is deep rut in the road to perfection.

    But back to the plot: A sub recommendation that only provides oomph below 40Hz?

    Anybody? :)

    Nimby
     
  5. Spearmint

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    Hi Maki...

    I take it you want to run your mains as large, if this is the case you should add an external xover to enable you to blend the sub with the mains.
     
  6. Maki

    Maki
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    Stick with me on this,I am new to subwoofers, a little more detail about the last suggestion would help. I take it, it means the crossover being the point where the sub takes over from the main speakers?
     
  7. Nimby

    Nimby
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    Correct. As the sub rises in frequency it is rolled off. As the speakers fall in frequency they are rolled off. There is usually an overlap as the roll-off slopes cannot be vertical.

    I don't see why you need an external crossover.

    Use your receiver to set the crossover frequency.

    Set the speakers to large.

    Set the crossover frequency quite low to allow the main speakers to add their own muscle to the bass.

    Nimby
     
  8. Spearmint

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    Hi Maki...

    The general rule of thumb is you should xover your mains at approx 1 Octave above the -3dB point of your main speakers.

    If your mains go to 40 Hz you should set them as small and the xover @ 80 Hz. As Nimby has said the xover's are not a brick wall and the mains are still outputting sound down below the xover point.

    The point of the external xover was if you were going to set your mains to large, this allows a more flexible adjustment of the xover frequency and slope.
     
  9. Maki

    Maki
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    Thanks for the advice, it is all pretty much as I thought. So what are the suggested sub's?
    It's looking like a fairly beefy sub is required.
     
  10. antdavis

    antdavis
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    when i was useing q55's i was using an eltax atomic A12 sub they seemed to blend pretty well together.:thumbsup:
     
  11. ridd

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    Hi,
    My sub belnds very well with my Q7 speakers just using my processors cross over (set @80hz)
    Any svs will fill that room fairly easily.
     

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