How to Use SPL Meter

Discussion in 'Speakers' started by Daman, Feb 13, 2004.

  1. Daman

    Daman Second Unit

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    Hi Everyone,
    Am planning to buy Radioshacks SPL meter and calibrate my speaker settings... i tried to do a search on the older threads but could not find a mention of how actually to use the meter to get optimum performance.. can anyone suggest or guide me how to do it? I do get it that i should preferably put the meter on a tripod at the place where the listeners head would be.. and probably set the weight to level C and response to slow.. and for each dB try to adjust the speaker volume so that the meter shows 0dB?? Am i right or missing something.. please help!!
    Thanks
    Daman
     
  2. Justin_D

    Justin_D Stunt Coordinator

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    The SPL meter is best used in conjunction w/ a calibration dvd such as Avia or Digital Video Essentials. Its in the Primer. They can be had at Amazon.com among other places...

    Oh yeah, and the DVD will walk you through how to use it
     
  3. Daman

    Daman Second Unit

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    ive ordered a sterophiles CD which has pink noise to calibrate the system.. but till it comes i suppose if i listen to a cd with a rich spectrum i still would be able to adjust it to a certain extent right?? All i wanna know is how to go about it..
    Thanks [​IMG]
    Daman
     
  4. Angelo.M

    Angelo.M Producer

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    You can calibrate by using your reciever's test tones; you don't necessarily need a calibration DVD.

    You should keep the SPL meter in your listening position during the entire test. The microphone should be pointed straight up or slightly forward toward the speaker you are calibrating. Personally, I keep mine straight up during the entire test, at about ear level, at my listening position.

    Choose a speaker as a reference. You might pick the right or left front channel or the center channel; your choice. Give that channel a constant test tone and increase the receiver volume until your SPL meter reads X dB; X could be 65 dB, 75 dB, or 80 dB or whatever. I believe 80 dB is a THX standard, but many folks use 65 or 75 dB. This is your "reference level." For example, I calibrate to 65 dB which correlates to -30.0 dB on my receiver's volume control.

    Now, move to the next channel and adjust its level until your SPL meter reads X dB. Do not adjust the volume of the receiver, adjust the level of the channel.

    Repeat for all channels.

    Bear in mind that there are some corrections to be applied when using Radio Shack's meter, but even without them you ought to be able to do a reasonable calibration and get all of the channels within 1 or 2 dB of each other.

    Hope this helps.
     
  5. Daman

    Daman Second Unit

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    Great!!! Thanks a lot Angelo.. this will indeed help me a lot.. will let you know how it went.Thanks Again [​IMG]
    Daman
     
  6. BradD

    BradD Stunt Coordinator

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    What cd is this? Where did you order it from?
     
  7. Cameron Yee

    Cameron Yee Executive Producer
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    According to the Video Essentials instructions, the meter should be facing forward the whole time, not turned to face each speaker. You might have meant this, but your wording could confuse.
     
  8. Angelo.M

    Angelo.M Producer

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    Actually, I keep the meter pointed upward during the entire calibration.

    Some people advocate keeping it tilted forward the entire time, and some people advocate pointing the meter toward each speaker during its calibration. I suspect there will not be great differences with any of these methods.
     
  9. Robert_Dufresne

    Robert_Dufresne Stunt Coordinator

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    Pointing the meter upwards will give you a retter reading. pointing it forward would not give you an accurate reading on surround speakers.

    Robert
     
  10. Garrett Lundy

    Garrett Lundy Producer

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    Is it true that you need to add or subtract a few db's from the subwoofer reading because the SPL-meter can't work with bass tones very well?
     
  11. Edward J M

    Edward J M Cinematographer

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    The meter is C-weighted. Without going into great detail, it will read progressively lower than the actual SPL as you go deeper in frequency.

    The meter also has some inherent inaccuracies that cause it to read even lower than the C-weighted curve would suggest. Provided below is a table with the frequency, the theoretical correction factors for the C-Weighted curve, and the commonly used RS Correction Factors. As you can see, there is a difference between the two and it grows larger as the frequency drops.

    Whether each RS meter will display the exact same offsets is up for discussion, but my hunch would be no. If you really want to know what the meter is reading at any particular frequency, get it professionally calibrated.

    Of course, professional calibration will cost you as much as the meter itself....so most people just use the RS correction factors as "good enough". Unless you are into serious audio measurements, I tend to agree.

    Frequency / C-Weighted CF's / Common RS CF's
    10.0 / 14.3 / 20
    12.5 / 11.3 / 16.5
    16.0 / 8.4 / 11.5
    20.0 / 6.2 / 7.5
    25.0 / 4.4 / 5.0
    31.5 / 3.0 / 3
    40.0 / 2.0 / 2.5
    50.0 / 1.3 / 1.5
    63.0 / 0.8 / 1.5
    80.0 / 0.5 / 1.5
    100.0 / 0.3 / 2

    Regards,

    Ed
     
  12. Phil Iturralde

    Phil Iturralde Screenwriter

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    If it's good enough for them (Mixing Eng's) to encode my DD/DTS-5.1/6.1 DVD's sound, ... it's good enough for me to REF Calibrate using their same REF Calibrated encoding SPL process!!!

    Phil
     
  13. Daman

    Daman Second Unit

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    thanks a ton guys.. bought the SPL meter yesterday for 35 bucks from Radioshack and calibrated the system as you said.. boy was i missing out on some of the finer details [​IMG] am very happy man now!!! THanks all of you!!
     
  14. DaleBesh

    DaleBesh Stunt Coordinator

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    I heard RS discontinued the analog sound level meters. Seems you are fortunate to get one. However, Sears now sells one for about the same price. Under the Craftsman label. Same basic unit, but somewhat less professional looking.
     
  15. Edward J M

    Edward J M Cinematographer

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    The discontinuation was short-lived and was just to blow out the current stock.

    Like a Phoenix rising from the ashes, the Rat Shack sound meter lives on, reincarnated with a sexy new housing surrounding the same old guts as before.

    http://www.radioshack.com/product.as...5Fid=33%2D4050

    It's a screamin' deal for $40. It's not good enough for serious measurements, but it works perfectly for the average HT enthusiast for channel balancing and basic sub calibration. An essential tool no one should be without.

    Ed
     
  16. Jeremy Anderson

    Jeremy Anderson Screenwriter

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    The manual for the new RS meter (available online) also addresses the fact that the microphone on these units is NOT truly omnidirectional. That's why I have always recommended that SPL meters be pointed slightly toward the center channel -- to bring all of your speakers as close as possible to the same off-axis angle.

    For instance, in my room if I point the meter straight up, the surrounds are about 70 degrees from the mic's center axis, mains and center about 90, and rear center about 40. If I calibrate this way, you can definitely hear that the surrounds (especially the rear center) are not at the same level as the other speakers. However, if I tilt the meter forward so that all 6 speakers are as close as possible to the same off-axis angle, I get a far more cohesive sounding calibration. I know the argument against doing this is that they don't calibrate this way in the mixing studio... but you have to consider that they likely aren't using Radio Shack meters to calibrate mixing rooms. I recommend that people try it both ways and see which sounds best to them.

    One question I have for owners of the new RS meter: The manual says that the meter response is flat to 32Hz. Does that mean the correction values have changed, or are they talking about the microphone's response?
     
  17. Edward J M

    Edward J M Cinematographer

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    "Flat" usually means +/- 3 dB. Not coincidentally, 30 Hz is the -3 dB point on the c-weighted curve (see the above chart in earlier post).

    The owner's manual for the "old" (OOP) RS meter shows the c-weighted curve, and you can see it starts to diverge from the baseline up around 100 Hz actually.
     
  18. Phil Iturralde

    Phil Iturralde Screenwriter

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    They do calibrate the analog RS Meter to their RTA using the standard test tone, ... and my brother has a friend that works for Dolby, so his friend Calibrated his RS analog Meter @ Dolby, and I Calibrated mine from my brother's. If I remember correctly, mine was a tad high on the scale.

    Phil
     

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