Sub Calibration Question

Discussion in 'Speakers' started by GregBe, May 10, 2004.

  1. GregBe

    GregBe Second Unit

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    I always read posts about sub calibration where HTF members calibrate their subs a little hot for movies vs. music. I am aware that when using a Radio Shack SPL meter for sub calibration it is off by about 3db.
    When people say they calibrate their sub 2-3db hotter than the other channels for movies, is that based on a corrected value or not. In other words, if someone says they listen to music flat and movies 2 db hot, are they at 72db and 74 db on the spl meter, or are they at 75db and 77db's. Or are they even more than that and at 72 and 77db's

    I will also ask the inevitable over asked question anyway. What do you calibrate at for music and movies?

    Greg
     
  2. Bill Blank

    Bill Blank Stunt Coordinator

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    Firstly, I use Rives Audio Test CD 2, the only test CD calibrated to correct the errors of the Radio Shack analog sound level meter.

    I goose the DTS and DD sub levels by 3dB and run everything else flat at "0". When setting speaker parameters in my pre/pro at the sweet spot, the results look like the following:
    FRONT LEFT: 0dB
    CENTER: -1dB
    FRONT RIGHT: 0dB
    SURROUND RIGHT: +1dB
    SURROUND LEFT: +1dB
    SUBWOOFER: 0dB

    I set my sub's volume level at the sub so that the above menu is at 0dB.

    I then go into the "SUB LEVEL" menu and adjust the Dolby Digital and DTS +3dB, leaving everything else at 0dB.

    Every processor's different so mine may not make sense.

    Bill
     
  3. Jack N

    Jack N Agent

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    I had my suspicions about the analog version of the RS SPL meter so I went with the digital version. I think it's off a little also, but not as bad. As far as my own personal settings go, I'm kind of wierd. I like bass, but I don't like how subs sound if they're set even the slightest bit too hot. I don't watch enough movies to stick in your eye so I don't bother with separate settings. I haven't heard a "musical" sub yet at any price. So after all the corrections and depending on driver size, power of the sub, etc. I run my subs no hotter than 1 db down. The rest are all set colder than that. I've devised a simple mathmatical formula that I loosely follow that seems to work fairly well. For any given sub, I figure out the number of square inches that the driver makes up, and then divide the wattage rating of the sub by the number of square inches of driver to come up with a wattage per square inch rating. I've found that the higher the rating, the cleaner the bass, and consequently set it closer to the threshold level. For example, one of the subs that I have (I currently use 4) is 15" in diameter. This converts to roughly 177 square inches. The wattage rating for that sub is 500, so when I divide 500 by 177 I get 2.8 watts per square inch. To me, this is a so-so rating so I've set that sub at -2 db after the corrections. I use 60 to 63hz as my reference tone for setting the output. Of course ultimately, it comes down to your own personal tastes. Like you, I'd be interested in hearing what kind of methods other people use for setting their subs?
     
  4. WayneO

    WayneO Supporting Actor

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    Most people mean 72-3ish would be flat, 74-75ish would be a touch hot. I use my receiver's test tones and they work fine. I've also used my DVD player's and DVE. All pretty much close enough to not call one source better than the other, though DVE's sub tone was recorded about 10db to hot, and makes calibration a little more difficlut, so I wouldn't recommend it.
     
  5. Edward J M

    Edward J M Cinematographer

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    A cool idea in concept. It is unlikely each RS meter will display the exact same offsets, but it's probably "good enough" for basic calibration.

    Regards,

    Ed
     
  6. Bill Blank

    Bill Blank Stunt Coordinator

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    Ed,

    As far as I know the errors of the RS meter are "standard" enough that the "corrections" have been out for some time. I used to use Stereophile's Test CD 3 and just apply the corrections on the spreadsheet. The Rives test disc makes it easier because they've already compensated for the errors in the tones and they use separate tracks for each frequency. The latter makes it much easier to tackle bass issues as you can simply put a problem frequency on REPEAT and fiddle around until it's correct.

    That was how I solved a -5dB null that was a result of incorrect phase. Thankfully SVS' subs include an adjustable phase as opposed to selectable.

    Bill
     
  7. Edward J M

    Edward J M Cinematographer

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    Amen to that, Bill. It's a very useful control and often the best phase setting ends up somewhere between 0 and 180.

    I've measured two RS meters thus far, and there were differences between them, but nothing huge that would totally blow a curve. Other people have reported different experiences, including one guy who stated the meter was off by 20 dB (IIRC) at 20 Hz, even after the RS CF was added. My response to that would be the meter was clearly defective.

    Again, for plotting a basic FR and looking for big peaks and nulls, I think the RS meter with CFs is "good enough". The owner could always get the meter professionally calibrated for about $45 and have a custom set of CFs developed for that particular meter, and still be under $75 for the whole show - not bad for that extra level of accuracy.
     
  8. Bill Blank

    Bill Blank Stunt Coordinator

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    Mine ended up 1 tick to the right of half-way.

    Sounds like that guy's meter was defective or dropped at some point, throwing the calibration off significantly.

    Bill
     

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