how to use spl meter

Discussion in 'Room Acoustics, System Layout & Setup' started by lestat0521, Jan 9, 2008.

  1. lestat0521 Audioholic Intern

    lestat0521
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    I have read a few articles on how to use the spl meter and cant seem to figure out how to use it with my system, i have an option for speaker levels but it keeps switching between two speakers, then i have a test tone option that i can cycle through each speaker individually but here are my questions:

    1) it says to put volume to avg listening level with a dvd or cd or some audio source, well i do and then when i go to test tones i don’t have 75 dbi worth of noise coming out of the speakers so i have to crank them up even more. To get to 75dbi, is this ok?

    2) my front speakers, left and right do not have a +dbi range only negative so i have to use them as my starting point for my 75 dbi source correct or incorrect?

    3) Should i point the spl at the speaker i am testing or in the air near my ear level?

    thanks.
  2. MDS Audioholic Spartan

    MDS
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    The SPL meter should face straight up and be close to ear level. Putting it on a tripod is ideal so you can stand behind it and not have your body affect the measurement. The meter should be set to C weighting and Slow response.

    Initially each channel level should be zero. If the fronts only have negative offsets then every other channel will adjusted relative to them. Where you set the master volume control depends on the receiver. If the volume scale is relative (-something to +something) then you use 0. If the volume scale is absolute (0 to something) then pick a point that is about 80% of the range. If the receiver is THX certified, it will automatically be set to 0 so it doesn't matter where the master volume is set.

    Then start the test tones and adjust the levels as closely as you can to read 75 dB on the meter. That gives you reference level when the master volume is set to whatever number you used for the calibration. The test tones will automatically move to the next channel after a few seconds but don't worry about it - when it changes adjust that channel as best you can until it moves to the next channel. It will take several full cycles for you to get each channel about level. Your remote may also have a 'channel select' button to move to the next channel manually.
    MDS,
  3. Savant Audioholics Resident Acoustics Expert

    Savant
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    All good advice, save for the orientation of the meter, which won't matter unless the meter is VERY old. Most every inexpensive SLM these days has a random incidence microphone. Random incidence means it can be pointed in any direction and still accurately measure the sound level at the location of the microphone. Align it so the display can be read easily. Otherwise, happy measuring! :D
  4. MDS Audioholic Spartan

    MDS
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    Thanks for the info on random incidence microphones.

    I've had my Radio Shack meter for years and everthing I've read about its use including its own documentation says to point the microphone straight up. Is the RS digital meter old enough that it might not use a random incidence microphone?
    MDS,
  5. Savant Audioholics Resident Acoustics Expert

    Savant
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  6. iTarik Enthusiast

    iTarik
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    Tx-sr605

    Sorry to barge in your thread but I kinda have the same question about the SLP.
    I have the TX-SR605 Onkyo and I wanted to calibrate it using the SLP but cant figure out how to do it ( Total noob to this HT goodness).
    Can anybody who calibrated his or her onkyo 605 with SLP show me how they did it?
    Step by step instructions would be greatly appreciated.
    Thanks.
  7. iTarik Enthusiast

    iTarik
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    When I raise the master volume lets say 70 it shows 70db on the SLP, is this how its supposed to be?
    if so, dont I just set the speakers levels to 0db and just adding +5 dbs to each and everyone of them would set the SLP calibration to 75db?
  8. Savant Audioholics Resident Acoustics Expert

    Savant
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    If your receiver volume display says 70 and your sound level meter (SLM) reads 70 dB(SPL), it's purely coincidence...unless you initially set it that way using the trims on each channel.

    However, if the volume display increments in dB, then you should notice that the sound level display on your SLM correlates with the receiver volume display as long as you don't move the microphone. If you do move it to another spot in the room, 70 on the volume display might correspond to, say, 72 dB(SPL) on the SLM. But as long as the volume display is in dB, you will still see a 1:1 change on the SLM. I.e., turn the volume up to 72 and the SLM should now show 74 dB(SPL). There are other factors/variables to consider that I am ignoring right now (e.g., relative contribution of reflected energy), but generally this should be the case.

    In order to "calibrate" your receiver, you should already sort of be there. If you have 70 = 70 for a certain microphone location, then there should be 1:1 correlation of any other volume settings, provided the receiver volume display increments in dB.

    FWIW, I would not call this "calibration" so as not to confuse it with the actual calibration of an SLM. I would call this "correlation"; correlating the volume display reading with an SLM reading. Once again, provided the volume display increments in dB, there should, in general, be correlation. E.g., some receiver volume displays top out at 0 dB, with negative values below that. What one decides to use as the starting point in that case is arbitrary. One could match -25 dB volume display to 70 dB(SPL) and have 1:1 correlation from that point.

    Make sense?
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  9. MDS Audioholic Spartan

    MDS
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    What Savant said. :)

    But to elaborate a tiny bit further...while you could theoretically use any number in the range of the volume control as your 'reference' setting, in practice it isn't possible because the channel trims have a limited range of adjustment - typically +/-12 dB. In other words, you are not going to get 75 dB average level with a master volume setting of say 40 when the scale is 0 - 100 unless the room is very small and you are sitting right on top of the speakers.

    You should pick a number around 80% of the range to use as the reference volume setting. Once it is calibrated each increase or decrease of the number on the volume display should increase or decrease the SPL by 1 dB.
    MDS,
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  10. iTarik Enthusiast

    iTarik
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    It does. My receiver volume is in numbers. So, if I set my receiver at 70 or whatever to make sure the SLP display 0 or (mid) ,then I start adjusting the speaker volume settings until I reach +5 meaning 75db and That should be it. right?
  11. captiankirk28 Full Audioholic

    captiankirk28
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    Thank you a great thread i just set my spl and it makes a huge difference, i have new speakers all over again!
  12. MDS Audioholic Spartan

    MDS
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    70 on the receiver volume display would be your reference setting and if you calibrate so that the meter reads 75 dB when playing the internal test tones then whenever the volume is set to 70 you will get 75 dB SPL...but here is the catch and something that is often overlooked:

    The test tones are at a level of -30 dB. This is digital audio and 0 dB is the top of the scale. So when the level of whatever you are playing is around -30 dB (average level of dialog in a movie), you'll hear 75 dB SPL. When that level increases, so will the SPL. When the level peaks (hits 0 dB) your output SPL will be 75+30 = 105 dB which is the definition of Dolby Reference Level. If you listen below that 70 reference number the output SPL will be correspondingly lower. If the source you are playing has an average level higher than -30 dB (nearly ALL modern CDs) the math is the same but it will be much louder because it was higher to begin with - if you whisper into a megaphone your voice gets amplified but not quite as much as when you scream into the megaphone. [Silly example, I know, but that is a simplistic way to describe digital audio levels that are then amplified].

    If you are talking about the Radio Shack meters (I'm sure others are similar) you set the mid-point of the range it will measure. So if you set the meter to a range of 70 it will measure between 60 and 80 dB. In the case of the digital meter it will read the exact number. In the case of the analog meter when the needle is on zero it is the range you set it to (70 in this case) and if the needle hits +5 it is 75 dB.
    MDS,
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  13. iTarik Enthusiast

    iTarik
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    Got it. Thanks
  14. gijoela Audiophyte

    gijoela
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    Question...

    I have a Elite 94TXH and I am trying to calibrate the sound. I bought a radio shack digital meter and have the settings at C and slow weighting..Now, how bout the meter sound level settings? 60? 70? 80? etc?

    Are you familiar with the DVE essentials disc for HD DVD or Blu Ray? Are they better to use to calibrate the sound than the internal MCACC system?

    Any help is greatly appreciated..

    -joe
  15. Savant Audioholics Resident Acoustics Expert

    Savant
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    joe,

    Those numbers represent the center of the SPL range for the meter. E.g., "60" sets the meter to measure between 50 and 70 dB (A or C, depending); "70" sets the meter to measure between 60 and 80 dB; and so forth. Either the "70" or "80" setting should work if you're calibrating to a 75 dBC signal.

    Unfortunately, I am not familiar with the DVE essential disks. Using the internal calibration signals from any receiver usually works fine, though, IME.
  16. billy p Audioholic Ninja

    billy p
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    Speaker set up

    Hey guys quick question about using a SPL metre and setting up speakers. If I use the metre to properly calibrate SPL from each speaker than would it be counter-productive to set the time delay or distance via the receiver?
  17. Savant Audioholics Resident Acoustics Expert

    Savant
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    No. Time delay will not affect the sound level calibration process. The delays should be set appropriately via the receiver.
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