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Advice on using SPL to set up HC

Discussion in 'AV Receivers & Amplifiers' started by NickBull, Apr 25, 2002.

  1. NickBull

    NickBull
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    Just got an SPL meter and need a bit of advice. I know that the mike needs to be about where my head will be. But should I keep it pointing towards the front of the room, or point at each speaker as I calibrate?

    Cheers

    Nick
     
  2. Ramius

    Ramius
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    Hi Nick.

    Either point the thing straight up or straight up and leant forward at 45 degrees.
    Keep it in that position for the full calibration.

    Don't point it at each speaker.

    Cheers
    Boris
     
  3. Timh

    Timh
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    Is it improtant to have the volume set to a perticuler level, I am sure I read somewhere that it should be set at 75db's, is this true?
     
  4. mcmullanbrush

    mcmullanbrush
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    thanks nick, i was about to post the same question, and i am also unsure about the level, i too have heard 75db, is this correct it sounds very quiet
     
  5. NickBull

    NickBull
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    I think the Denons set the Test tone volume, not sure at what though. I'll try 75 and also do it again at about 90, see if it makes a diff
     
  6. Dubbing Mixer

    Dubbing Mixer
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    The mic on most spl meters is nominally omni directional so, in theory it shouldn't matter which way you point it. In practice, I've watched Dolby film engineers lining up rooms and they usually point it forward at ear height in the 'hot seat'.

    As to the exact level, this matters less. There are endless threads discussing exactly what it should be but the really important thing is that the LCR and surround speakers should all be at the same SPL. If you want to calibrate exactly, you need to know the relationship between the test tone (pink noise) level and peak level. Then you can make a meaningful calibration. Check out Dolby's web site or Tom Holman's (THx for the in depth version of this.
     
  7. Dubbing Mixer

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    PS to last post:

    And the most important thing is let your ears be your guide. Room acoustics play a large part in this and if one channel sounds louder than the others even though it measures the same, drop it back a bit.
     
  8. bh

    bh
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    THX Reference Level and SPL settings from http://www.audiovideo101.com/dictionary/thx-reference.asp

    "Volume level designated to be used as the standard in THX certified theaters and home THX installations setting volume at 85 decibels when fed a continuous test tone and achieving 105 decibel peaks when the volume control is at the reference 0 decibel setting. The 0 decibel setting is the reference on the volume control with negative numbers being the number of decibels below reference and positive number being the number of decibels above reference. The reference level is set using a test tone generated by a surround sound preamplifier and a sound pressure level meter (SPL meter) to measure the sound output or volume.

    While providing a realistic and enlivening auditory experience, the reference level is very loud and is often turned down somewhat by listeners. However, surround sound audio systems should be set to the THX reference level and all channels properly equalized (each channel putting out the same sound pressure levels with a reference signal) even if the system will not be listened to at the true reference level. It is an interesting exercise to demonstrate a home theater system for friends when it is set at the true THX reference level though. "
     
  9. Dubbing Mixer

    Dubbing Mixer
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    Once again, this fails to mention what level the test tone should be at and fails to take into account factors such as speaker sensitivity. I think they are assuming the test one is at 'standard THx reference level. The only way this approach works in domestic circumstances is where the reference level is a known quantity and there is an independent level tweak for each amplifier channel after the master fader. Some domestic amps do provide this and some don't.
     
  10. Ramius

    Ramius
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    Hi

    We do know what reference level is and we also know what level the test tones are recorded at.

    Dolby Digital reference level is 105dB for the main channels and 115dB for the LFE, these are measured at the listening position.

    The test tones are recorded at -30dBfs (or 30 below full scale) for the Video Essentials calibration DVD and most receivers/processors.

    The Avia calibration DVDs test tones are recorded at -20dBfs (20dB below full scale).

    That's where the 75dB and 85dB values come from.

    Both methods will give the same results.


    I use Avia, I highly recommend it, and accurate calibration.
    It's one of the best tweaks (if you call calibration a tweak) you can do.

    Make the most of your equipment.

    Cheers
    Boris
     

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