Which ICBM slope for SVS subwoofer ?

Discussion in 'Archived Threads 2001-2004' started by Steve McWilliams, Nov 7, 2001.

  1. Steve McWilliams

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    Am I correct in thinking that the SVS subwoofers are not THX certified, and thus I should leave the ICBM crossover slope in the Normal position, rather than the steeper Special position ?
     
  2. John Kotches

    John Kotches Cinematographer

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    Steve,
    I have a CS Ultra that I used as part of my (just published) ICBM review at Secrets of Hometheater and HiFi.
    I could detect no substantial difference between Normal and Special mode with the ICBM.
    It's mainly about dropping the subwoofer out of the picture faster. You can try it in both positions and see what your own preferences are.
    Regards,
    ------------------
    John Kotches
    Contributing Writer
    Secrets of Home Theater and High Fidelity
     
  3. Steve McWilliams

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    Thanks, John. I plan on charting the response curve as soon as I get time. I'll go with whichever setting(s) give me the best blend. Sounds like it may not be that critical in most situations anyway, if you couldn't tell any difference.
     
  4. Lewis Besze

    Lewis Besze Producer

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    What's order rate on those slopes?
     
  5. Steve McWilliams

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    The Normal slope is 12db per octave and the Special is 36db per octave.
     
  6. Steve McWilliams

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    Of course, now that I get home and try to balance the volume levels, it appears that my ICBM is defective and I will probably have to return it. No sound comes out of the subwoofer or center channel paths (from the Kenwood 5900M to ICBM to Denon5700). The other channels are fine, all channels set to Large in the DVD player, Bypass or any other setting on ICBM. Going directly from DVD to Denon for Center channel produces sound. Putting the ICBM back in the path and rechecking connections, still no sound in Center or subwoofer.
     
  7. Espen Braathen

    Espen Braathen Stunt Coordinator

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    "The Normal slope is 12db per octave and the Special is 36db per octave."
    To bad they don't offer the industrial standardized 24/octave slope as "normal". Instead you got the extremes at either end: 12/octave slope is just not very usefull at the 80 Hz x-over point and 36 db/octave will not ingegrate well with the high pass filter cut off in most set-up's.
    Espen
     
  8. John Kotches

    John Kotches Cinematographer

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    Yes and no Espen....
    By the time you get out one octave above the crossover frequency at 12, 24 or 36dB / octave you're getting a minimal contribution from the subwoofer.
    Also, correctly employed, there are no other crossovers in the signal path, which would interfere with the ICBMs setup.
    The math works out to about 6% at 12dB/octave contribution at +1 octave, much less than 1% at 24 and 36dB/octave.
    Regards,
    ------------------
    John Kotches
    Contributing Writer
    Secrets of Home Theater and High Fidelity
    [Edited last by John Kotches on November 07, 2001 at 10:37 PM]
     
  9. BruceD

    BruceD Screenwriter

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    Isn't the phase offset the biggest issue with both of the ICBM settings? Which makes it harder to smoothly integrate subs with mains.
    Both 12dB and 36dB have wicked phase offsets compared to the zero phase offset offered by Linkwitz-Riley 24dB filter slopes.
    BruceD
     

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