Sub Calibration with an SPL Meter

Discussion in 'Speakers' started by AlexanderS, Mar 5, 2004.

  1. AlexanderS

    AlexanderS Second Unit

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    Hey guys. Im trying to calibrate my HC6 sub. Ive managed to calibrate my other speakers to 75db but when I keep that same setting and switch to my sub the SPL meter goes off the charts. I have the subwoofer level at around 40% eyeball, the crossover turned to max and at 120 in the receiver, and the phase on 0. Am I doing something wrong or is the level too high? Thanks.
     
  2. Nathan Stohler

    Nathan Stohler Second Unit

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    It's too high.

    My subwoofer doesn't have any tick marks for the level control, so I set it squarely at 50% (12 o'clock) to make it easy to remember, and I set the subwoofer to -5 dB on my receiver.

    A lot of people find that when they calibrate their system, they had their sub level too high. I certainly did. If you prefer a higher level of bass, there's nothing wrong with running it that way.
     
  3. Kevin C Brown

    Kevin C Brown Producer

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    In fact, because the Radio Shack meter is less sensitive at lower freqs, you should actually adjust the sub's level so that it is a few dB's *below* 75 dB.
     
  4. Phil Iturralde

    Phil Iturralde Screenwriter

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    The recommendation from Dolby Labs (my brother's friend works there) is start @ 75 dB for either their DD-EX and original Video Essentials DVD(s) dedicated LFE test tone and see if that balances well with your HT system. If it's sounds a bit anemic @ -10 dB below REF Level, ... then add 1 or 2 dB or more LFE trim until you're happy and it's not boomey, overbearing or bloated. Overall balance is the key!

    In my case, I've set my SVS 25-31PCi @ 77 dB (lowest needle swing 76 dB / highest 78 dB) using Dolby Labs DD-EX dedicated LFE test tone & @ -10 dB below REF Level, ... it sounds glorious!!! [​IMG]

    Phil
     
  5. AlexanderS

    AlexanderS Second Unit

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    So I should use the level's in the receiver and not on the back of the sub? Maybe set the sub's level at 50% and adjust the receiver's output?

    When measuring do I keep my receiver at ref level and adjust the sub level's from there or should I back down the volume? Thanks.
     
  6. Edward J M

    Edward J M Cinematographer

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    The AVR master volume should be kept at Reference Level for ALL channel balancing and calibration. Never touch the Master Volume control - only adjust the channel levels. In the case of the sub, see above.

    If you are using a calibration disc, you will be shooting for either 85 dB (S&V and Avia) or 75 dB (VE).

    The DVE disc has (or had) a serious subwoofer calibration tone problem. It was mastered at too high of a level. Go here for more information:

    http://www.hometheaterforum.com/htfo...hreadid=184659

    Regards,

    Ed
     
  7. AlexanderS

    AlexanderS Second Unit

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    I thought the S&V disc used 75db? Thats what I used to calibrate with S&V and DVE.
     
  8. Edward J M

    Edward J M Cinematographer

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    No, Avia and S&V use 85 dB for Dolby Reference Level. VE and DVE use 75 dB for Dolby Reference Level.

    The Ovation products are encoded at -20RL, and the JKP products are encoded at -30RL. Hence the difference in volume requirements when calibrating for RL.

    You can certainly use 75 dB for Avia or S&V. The Master Volume setting at this point will just be -10RL.

    Many people listen at -10RL anyway, so there is really no problem doing this.

    Personally, I always calibrate to RL at Master Volume 0.0 so it's easy to do the math in my head when discussing playback volumes. -10 on my Master Volume is exactly -10RL, and so on.

    Ed
     
  9. AlexanderS

    AlexanderS Second Unit

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    Well I went ahead and calibrated with S&V. I set my receiver to -5 and sent the level tone out. I ended up with my receiver at -4 and my sub level around 35%. I couldn't nail down a reading though. It kept fluctuating so I went with the setting that fluctuated between 70 and off the scale. What do you guys think?
     
  10. Kevin C Brown

    Kevin C Brown Producer

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    Play some CDs and DVDs that you are familiar with and see how it sounds. Adjust from there.
     
  11. Edward J M

    Edward J M Cinematographer

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    I assume you're going with 75 dB at all channels?

    If so, set the RS meter to the 80 scale on C-weighted Slow. It will fluctuate far less and will be easier to get an average reading.

    On the 80 scale, the -5 point on the meter will be 75 dB.
     
  12. Lev-S

    Lev-S Second Unit

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    what about Ultimate dvd platinum? What ref level (75 or 85)
     
  13. ScottCHI

    ScottCHI Screenwriter

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    below or above?
     
  14. Kevin C Brown

    Kevin C Brown Producer

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    Below. Think about this way:

    The meter is less sensitive to low frequencies, so that means that to get an equivalent reading, the sound level at those frequencies actually has to be louder to get the same reading as higher frequencies. So you adjust downward to compensate. I think the going number for most sub test tones from pre/pros, Avia, etc, is 3 dB.

    Think about it for a moment and you'll get it. Does seem opposite from what you'd think. [​IMG]
     
  15. ChrisBee

    ChrisBee Stunt Coordinator

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    If you calibrate with the same tone on both main speakers and subwoofer (say 80Hz) wouldn't that achieve better accuracy?

    Since you would be measuring like with like (same frequency on both sub and mains) you wouldn't even have to think about compensation for SPL meter roll-off errors. The errors would be nulled.

    The sub and mains should be able to manage 80Hz within their flat power bands for this to work of course.

    Too simple? Or have I completely lost the plot? [​IMG]

    ChrisBee
     
  16. Phil Iturralde

    Phil Iturralde Screenwriter

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    The signal used in your AV Receiver Internal Test Tone, Dolby Labs EX-Test Tone DVD, VE, DVE & Delos DVD Spectacular test tones are recorded -30dBFS++ (Dolby Labs spec) using pink noise**.

    (AVIA & Sound and Vision Tune-up DVD test tones are recorded -20dBFS using pink noise.**)

    **pink noise : A type of random noise which has a constant amount of energy in each octave band, as opposed to white noise, which has equal energy at all frequencies. Pink noise can be made from white noise by passing it through a filter with a 3dB per octave rolloff. Pink noise is used to align the frequency response of tape recorders and loudspeaker systems.

    ++So, like I said before, Dolby Labs just recommends REFERENCE Calibrating their recorded -30dBFS test tones @ 75 dB (align all-your speakers @ 75 dB - basically equalizing the SPL's // AVIA & S&V @ 85 dB) including the LFE Test Tone (Delos DVD Spectacular does not include one). No need to compensate for the RS errors, ... just read the SPL Analog Meter.

    Mark down the AV Receiver's LFE Test Tone value, and adjust afterwards by tweaking it up or down per your preference. Your sub placement and room plays a big part with your preference.

    Since the LFE pink noise Test Tone is long, the AVG would be approx. the middle of your needle swing. The swing can be 3 dB total like in my HT/family room (77 dB SPL - lowest needle swing 76 dB / highest 78 dB) , or more. Just take note the highest SPL swing vs. your lowest SPL swing and your LFE AVG is the middle SPL.

    Phil
     
  17. GregBe

    GregBe Second Unit

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    Thanks Phil,

    For what it's worth, I took your advice and I recalibrated my sub at 77 db. I previously had it at 80 db. It is amazing what only 3 db makes. My system sounds so much more balanced now. At first I thought that since I spent so much money on a sub, why not set it for as much impact as I could. Then I thought to myself, with that logic, where do you stop. Every uptick in sub gain gave me more impact. At some point you have to say enough. At 77 I get impact where I need it, and not where I am not supposed to have it.

    I have 2 questions for you.
    1) Do you leave your sub at 77 for music as well?
    2) Do you leave it at 77 no matter how low you play your volume? Typical listening for me is at -15 to -20 below reference, but sometimes at night I listen to -35 to -40. Do increase your sub volume?

    Greg
     
  18. Phil Iturralde

    Phil Iturralde Screenwriter

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    Well, based on my SWFR & LFE Calibration procedure above, the answer is NO, I don't change my LFE (DVD) or SWFR (2-channel Music CD; etc.) controls levels! Some software will be mixed hotter (i.e. DVD's with more LFE SPL - like "Lord of the Rings") than others, so I use my SPL Meter to monitor the DVD SPL levels @ my 'sweet spot', usually lowering the level's until I get approx. 105 dB to 106 dB of Fast SPL LFE peaks during the DVD movie. That roughly corresponds to approx. -10 dB below REF Level.

    FYI: Usually my REF Calibration Fast LFE SPL Peaks are as follows, ... with most DVD's which corresponds with my AV Receiver's Volume Control digital read-out*:
    1) REF LEVEL = 115 dB (*AV REC = -20 dB)
    2) -5 dB below REF Level = 110 dB (*AV REC = -25 dB)
    2) -10 dB below REF Level = 105 dB (*AV REC = -30 dB) - my usual once or twice a month Friday NITE DVD presentation w/friends & family - loud enough to move the air, floor, couch, walls & pant-legs @ all my seating locations, but still be audible during the quieter movie dialog scenes during the DVD movie.

    Phil
     
  19. Kevin C Brown

    Kevin C Brown Producer

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    Bingo. For the longest time, I thought my sub was too loud for movies, but just right for music. (But music actually doesn't have much content below 40 Hz.) After I discovered the "trick" of dropping the sub a few dB, I felt the exact same way. Much better balance.
     
  20. Joe Mihok

    Joe Mihok Second Unit

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    Just curious, what's the frequency of the internal sub test tone (the one built into our digital recievers) ? Just curious cause I need to know how many db's to compensate with my radioshack SPL meter.
     

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