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Which Radio SPL meter is best, Digital or analog? Accuracy?

Discussion in 'Archived Threads 2001-2004' started by Chris PC, Sep 8, 2001.

  1. Chris PC

    Chris PC Producer

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    Wondering which Radio Shack SPL meter is best. Is there an accuracy difference between the 2 meters? Feature difference? Have you used both? Which do you prefer?
     
  2. John H

    John H Second Unit

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  3. Chris PC

    Chris PC Producer

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    Good point. Thats a neat feature. Otherwise, how does instantaneous accuracy compare between the 2 in your experience?
    [Edited last by Chris PC on September 08, 2001 at 09:17 AM]
     
  4. John H

    John H Second Unit

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    Both will do the job. Most prefer the analog version. It will measure changes below 1dB.
    John
    ------------------
    Bedroom Based Theater
    Looking through a glass onion
    [Edited last by John H on September 08, 2001 at 10:18 AM]
     
  5. Eugene Hsieh

    Eugene Hsieh Supporting Actor

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    BTW, does anyone have the link to the SPL correction factor table for those units? (I have the digital one.)
    ------------------
    Eugene Hsieh, VisorCentral FAQ Editor
    1000 km on a tank of gas??? Check out the Prius and drive the future now!
    Check out my switched Dual Boot DVD Player Hack.
     
  6. Mario_C

    Mario_C Stunt Coordinator

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    It makes me wonder why Radio Shack would not have the digital meter compensate numerically for the mic roll off. I mean could they program the Digita meter to account for this and add or subtract the proper dB? [​IMG]
    ------------------
    My Audio & Video System
     
  7. John H

    John H Second Unit

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  8. ThucN

    ThucN Agent

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    The manual that comes with the analog SPL meter contains a graph that shows the meter's response curve.
    From about 2 - 7 kHz, the meter is overly sensitive from about 2 - 4 dB. But at 10 kHz, the meter's response is down by 3 dB, and at 20 kHz is down by approximately 15 dB.
     
  9. Manuel Delaflor

    Manuel Delaflor Supporting Actor

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    I wonder which would be the "official" position from Radio Shack regarding the "correction file". I have their SPL meter and of course the file. But I always wonder about how exact it really is.
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  10. Eugene Hsieh

    Eugene Hsieh Supporting Actor

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    How were these values acquired by the way.
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    Eugene Hsieh, VisorCentral FAQ Editor
    1000 km on a tank of gas??? Check out the Prius and drive the future now!
    Check out my switched Dual Boot DVD Player Hack.
     
  11. Chris PC

    Chris PC Producer

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    Hmmmm. Interesting. Well, if I find an Analog one, I'll go that route cause its more than adequate for my purposes and less expensive.
     
  12. Eugene Hsieh

    Eugene Hsieh Supporting Actor

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  13. Mario_C

    Mario_C Stunt Coordinator

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    Has anybody used any of these more expensive SPL Meter form Radio Shack? I wonder if they are more acurate?
    SPL Meter 1
    SPL Meter 2
    ------------------
    My Audio & Video System
    [Edited last by Mario_C on September 10, 2001 at 01:38 AM]
     
  14. Guy Kuo

    Guy Kuo Supporting Actor

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    I'd get the lower cost analog rather than the digital if possible. The reason for that is it can perform hyperaccurate phasing tests of your speakers when set to "fast" response. The digital meter won't let you do the phase and speaker distance testing. BTW, that function is not described on AVIA but I'll append the instructions later. If you do the hyperaccurate phase test you'll get your main speakers into a few fractions of an inch phase and distance match. It is much more accurate than you can achieve stretching out a string because it actually balances the speaker to listening distances acoustically.
    If you're thinking about one of those higher end sound meters, then considier taking that same money and adding a mic and spectral analysis to your computer. You'd end up with much more detailed and useful information about speaker and room interactions than just mere SPL levels.
    Guy Kuo
    ------ snip ---------
    Using AVIA Phase Tests to Fine Tune Speaker Distance and Delay
    AVIA's speaker phase testing signals are also useful for very accurate adjustment of speaker delays and distances. You'll need an analog RS SPL meter set to fast response in order to take advantage of this tidbit. This may seem a bizarre way to check delays and speaker distances but it is surprisingly accurate.
    The phasing tests work by playing noise in the two channels being tested in phase and 180 degree out of phase intermittently. If the speaker distances and delays are both set correctly, then the in phase sounds from both speakers reinforce each other at the prime listening positioning. During the out of phase (diffuse) portion of the test, the sounds cancel. An SPL meter set to fast response can readily show the magnitude of the cancellation/reinforcement.
    Start by playing the Phase left front/right front signal. Move your SPL meter slowly left and right at your listening position. If you have set distance and delays correctly the maximal SPL delta will occur in the middle of your sitting position. I get about a 6 dB needle bounce on my system. If it happens right of center, then your right speaker is either too farther away than the left speaker or delayed more than the left speaker. Conversely, if the peak SPL delta occurs left of your prime listening spot, the left speaker is too far or excessively delayed.
    Once you have the front left and right speaker distanced and delayed exactly right, the SPL meter position at peak delta will be in the middle of your prime listening position. Note that position carefully. You'll need to be able to refer to that point within half an inch during the next step.
    Now comes the trickery that gets the center speaker also precisely phased and delayed. The AVIA disc also has a Phase Left Front/Center test. We can take advantage of it to bring all three front speakers into very tight phase alignment. From the previous step we already know where the two front main speakers are in phase. Leave the left and right delays and speaker positions alone now. We'll next adjust the center speaker to be in phase with the left front. This places all three into phase.
    Play the Phase Left Front/Center test and once more move the SPL meter left and right to find the maximal SPL delta point. Compare this new position to the one for the front mains. If all is perfect, they exactly coincide. If the left/center maximal SPL delta point is left of the left/right point, then the center speaker is either too close or insufficiently delayed. If the left/center max delta point is right of the left/right max delta, then the center speaker is too far. Move or adjust CENTER channel delay as needed to get the left/center max SPL delta to occur at the exact same place as for the left/right channels.
    Your left, center, right speakers are now in phase. You'll probably note that a 1 msec adjustment in channel delay makes for a considerable shift in max SPL delta position. After all, that is about a 1 foot speaker distance equivalent. Use very small speaker movements to fine tune the center speaker into phase alignment.
    Put your head at the center of the max SPL delta position and listen to some stereo and 5 channel material. You will be pleased with what has happened to sound imaging in your system.
    Moving your speakers to achieve exact phase match isn't the entire story. One must also position the speakers with relation to room acoustics to smooth frequency response. Sometimes, moving speakers into exact phase also moves one or more of them into positions that yield uneven frequency response. In such cases, some compromise is needed to address both imaging and frequency response concerns. Happily, the home theater sound processor does have delays and these can sometimes help bring speakers into phase, while still keeping them closer to best tonal balance position.
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    Guy Kuo
    www.ovationsw.com
    Ovation Software, the Home of AVIA DVD
     
  15. John H

    John H Second Unit

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    Guy,
    Will your phase alignment technique using the Analog RS meter work with bipolar mains and a monopolar center?
    John
    ------------------
    Bedroom Based Theater
    Looking through a glass onion
     
  16. Guy Kuo

    Guy Kuo Supporting Actor

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    Yes. What it relies upon is the speakers having matching frequency response in the relatively narrow band in which the test tones lie. If you have good acoustics and matched speakers, the test should work. If speakers are poorly matched or the acoustics are wacked, then you won't see the nice peaks and nulls as the signal goes in and out of phase. If that's the case, you also won't get as sharp sonic imaging either so it's to ones benefit to get the speakers being examined to match sonically. Bipolar or direct radiating, the speakers should mirror each other in frequency response and phase or you are intentionally altering the sound.
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    Guy Kuo
    www.ovationsw.com
    Ovation Software, the Home of AVIA DVD
     

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