Calibration and PC-Ultra

Discussion in 'Speakers & Subwoofers' started by Johnal, Sep 3, 2005.

  1. Johnal

    Johnal Stunt Coordinator

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    Hey People,
    I recently re-arranged my room and am going to calibrate my setup yet again. I'm not sure why things are so different but I think it may be a problem with the phase and/or my needing to use the PEQ. When using the Avia disc and am making the SPL meter read the same between my main speakers and the sub, my sub's Gain is having to be turned down to the second bar (as opposed to being between the third and fourth)if not lower to make it read the same 85db without going way over. I also set my receiver to read +/-0 so it's not even getting an extra boost there. Anyway, maybe i just have the sub placed in a more efficient location than before.

    Oh, and here's the final question...once i have the sub setup and calibrated to read the same 85db using the avia disc, is it safe to say i could watch just about any movie at reference level without having to worry about the PC-Ultra bottoming out? I've been wanting to watch a movie at reference level for a long time, but i've always been scared to hear that dreaded "slap" sound.

    -Johnal
     
  2. Lee-c

    Lee-c Second Unit

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    Johnal:

    It is generally recommended that you set your subwoofer channel level on your receiver to -5,
    not +/-0. This is so that you get a very clean minimally boosted signal sent from the receiver
    to your sub. While 0 might seem like no boost, when you consider that most receivers have
    a range of channel level adjustment from roughly -10 to +10 you can see that 0 is actually half
    way up to full boost on the subwoofer channel level. So -5 should provide a cleaner signal.
    This will also mean that you'll have to turn up your gain a bit on the sub to make up for
    the lower channel level, but you have tons of extra gain available on the sub, so that's no problem. [​IMG]

    Also, if you want your sub to be calibrated accurately flat to Dolby Digital Reference Level
    with Avia, then you should calibrate your sub to 82dB, not 85dB, with your Radio Shack SPL
    meter (I assume you are using a RS meter). This comes straight from Guy Kuo, who is
    one of the tech guys who made the Avia disk. The reason you calibrate to 82dB (meter set
    to slow response, and C weighting) and not 85dB is because the RS meter is somewhat insensitive
    to the subwoofer test signal that Avia uses, so when the meter says 82dB, it's really measuring
    at a true 85dB level.

    As far as Reference Level goes, it depends on how big your room is and how close you are
    sitting to the sub, but the powered SVS subs generally are quite hard to bottom out. I guess
    because the built-in amps and subsonic filters are tailored to match the sub's overall
    design so well. And the Ultra driver is especially resistant to bottoming out. If your room
    is not that big and/or you are sitting right next to the sub, then I think bottoming out
    is pretty unlikely. But to be safe, try watching some movies at several dB below reference,
    and see how things go. You may well find that you don't even want to watch many of the
    more intense action movies at full reference because everything (not just the bass)
    is so very loud at that level.

    Hope that helps. [​IMG]
     
  3. Johnal

    Johnal Stunt Coordinator

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    Thank you so much for your EXTREMELY helpful response. The weird part is that I recall reading most of what you explained to me because I beleive I did it properly the first time I calibrated my system. I guess thinking that this was my second time doing it it should be no problem, I made a noobie mistake :-/ Thanks so much again...can't wait to get home and get it goin right!

    -Johnal
     
  4. Lee-c

    Lee-c Second Unit

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    No problem, Johnal. [​IMG]
     
  5. Lee-c

    Lee-c Second Unit

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    Johnal: How did things go with your recalibration and watching movies at full Reference Level? [​IMG]
     
  6. Johnal

    Johnal Stunt Coordinator

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    Thanks to watching LOTR at reference level (w/no problem by the way) my cat sits in her cat tree whenever I am watching a movie. It was fantastic! [​IMG]
     
  7. Lee-c

    Lee-c Second Unit

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    Yeah, the LotR films are not only great movies, but they have some of the most intense bass around.
    I find -8dB to -6dB to be about the max volume I like on them, not because of the bass, but just because
    all the normal higher frequency sounds are already super loud at that volume setting. [​IMG] It's cool
    to see the PC Ultra handling such a difficult task so smoothly. [​IMG]
     

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