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Calibrating

Discussion in 'Home Cinema Speakers' started by StephenR, Jan 22, 2001.

  1. StephenR

    StephenR
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    I plan to add a subwoofer to my system in the very near future but I am unsure how to adjust my system using Video Essentials. I haven't actually used it with an SPL meter but I plan to do so when I add the sub - but I'm not sure how to use one! What exactly does the process involve?

    It may sound like a stupid question but I don't really know how to adjust my system - my DVD player has a built in Dolby Digital decoder and for the settings you just specify the distances of the speakers from the listening position. How does this relate to delay times etc? Do I just keep fiddling with the settings until ... well, until what? Until the readings on the meter are equal for each speaker? But what about the subwoofer? Surely that shouldn't give the same reading?

    I'm quite confused about this matter, so I would be grateful if someone could explain exactly what I have to do. I've had a look at some web sites but they are a bit too technical - I just want to know the basics!
     
  2. dUnKle

    dUnKle
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    What you need to do is get an SPL meter
    Place the meter very close to were you sit and point the micrphone at the TV ( and center speaker )

    Run the test tone out of your amp for each speaker.

    Set the SPL meter to 70db and make sure that each speaker gives the same output ( 75db is a good start )

    Regarding the sub, try and have it set a few dbs higher, mines set at 80db. For more thoughts on subwoofer settings go and have a look at my REL Q100E thread below.

    Also it all makes more sense once you have the spl meter in your hand
     
  3. Mad Max

    Mad Max
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    Now I'm confused !!!!!!!!!!!!!!!!!

    Do you point SPL at the TV, or do you place it vertically ?????????????

    Please, don't just say one or the other... I hate not understanding why [​IMG] Back up you statement about either choice with some sort of explanation... thanks


    ------------------
    An adult is just a kid with expensive toys.

    Rui
     
  4. Gary Palmer

    Gary Palmer
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    You may need to check the instructions of the sound meter.

    The one I use (a pretty common Tandy/Realistic gadget) makes a point in the manual of your body not being too close to the microphone when you take the reading - presumably sound reflections off your body can mess up the measured values.

    According to the manual, the microphone is fairly evenly sensitive in all directions (not sensitive along a particular axis) so it's not so important which direction the microphone is pointing. This is probably especially true of low bass which is supposed to be non-directional (which is why in theory the sub-woofer can go anywhere in the room without messing up the soundstange).

    To be honest, I found that using a sound-meter produced a good balance for the main speaker settings but for the sub the measured value was way too loud even with the correct weighting (to emulate human hearing sensitivity) on the meter

    This could be my room or my sub. But it could also be that the sound meter is not as sensitive to low bass (i.e. 30Hz and below) so I end up with a sub that's too loud when the meter says it's flat.

    Soooooo, I tend to use a well known bass bit on a CD or DVD playing repeat A-B and then adjust by ear...

     
  5. Ramius

    Ramius
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    I got told to point it vertically (Radio Shack Analogue meter I'm talking about, the one from Tandy).
    Put a box or something on your main listening seat to raise the meter so the microphone is at about ear level, where you head would be. Stand it up on it's ass so it's pointing upwards. Sit on the floor or where ever so you can see the display and you're not blocking the path of the signal to the meter.
    The microphone is directional. Pointing it at a source will give a higher reading, so by pointing it forward would result in you rears being too loud.
    Holding it while calibrating can also give inaccurate results due to reflections from your body.

    Cheers.
     
  6. Ramius

    Ramius
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    Well there you go.
    Different answers.
    It's amazing what people tell you [​IMG]

    I'm going to test how directional it is tonight [​IMG]

    Cheers
     
  7. dUnKle

    dUnKle
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    Ok
    You point it towards the TV and front speaker and I tend to have mine pointed slightly ( but not much ) upwards.

    This is how I have ALWAYS done it and the reason is that its hard to see the display when you have it pointing at the ceiling
     
  8. Ramius

    Ramius
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    I tested the directionality last night.

    I put the SPL meter on a box on the listening position. The meter was stood up pointing to the ceiling. (C-weighting, slow).

    Results- L C F LR RR all measured the same. (I used 80 dB as the level).

    I then layed it down pointing forwards straight at my TV.

    Results- L C F now measuring 83 dB. LR RR still measuring 80 dB.

    3 dB is a lot.

    I'd say the mircophone is directional.

    Cheers.
     
  9. Jagular

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    Hi Stephen! ’got all that?

    If you are using the Radio Shack Analogue SPL meter from Tandy you might want to use the following correction table ’cos the meter ain’t quite as accurate as folks might think.
    Little point in using a (calibrated?) piece of test gear if it’s not accurate?
    Just remember! A tester is only as good as its operator and the last calibration that was done on it.
    This meter is not a professional device – just a tool for comparing similar sounds.
    But as a guide only, the following table should suffice:

    + means; add to the recorded response.
    - means subtract from the recorded response.

    10hz.....+20.0db
    12.5h....+16.5db
    16hz.....+11.5db
    20hz.......+7.5db
    25hz.......+5.0db
    31.5hz....+3.0db
    40hz.......+2.5db
    50hz.......+1.5db
    63hz.......+1.5db
    80hz.......+1.5db
    100hz.....+2.0db
    125hz.....+0.5db
    160hz......-0.5db
    200hz......-0.5db
    250hz.....+0.5db
    315hz......-0.5db
    400hz.......0.0db
    500hz......-0.5db
    630hz.......0.0db
    800hz.......0.0db
    1k.....…....0.0db
    1.25k..…..0.0db
    1.6k.........-0.5db
    2k............-1.5db
    2.5k.........-1.5db
    3.15k.......-1.5db
    4k............-2.0db
    5k............-2.0db
    6.3k.........-2.0db
    8k............-2.0db
    10k..........-1.0db
    12.5k......+0.5db
    16k.....…..0.0db
    20k.........+1.0db

    I hope this may be of some use.

    Rob.
     
  10. Ramius

    Ramius
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    Calibration discs, Avia, VE, use pink noise for channel balancing. So just read the meters display and use the 'slow' setting to avarage the needle.
    The meter is accurate enough for this.

    The correction chart is handy though, especially for testing your sub and plotting it's response.

    Cheers
     
  11. Jagular

    Jagular
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    "I thought I'd got the Motorbike,
    but it seems I've just got the Horn." [​IMG]
     
  12. StephenR

    StephenR
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    Thanks everyone for your replies. I think I'm a little clearer about it now, and no doubt it will make more sense when I actually get the meter.
     

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