Is my Radio Shack sound meter working properly?

Discussion in 'Archived Threads 2001-2004' started by Ben Jordan, Oct 7, 2002.

  1. Ben Jordan

    Ben Jordan Stunt Coordinator

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    I ask because I was watching Fight Club the other night with my Onkyo 787 set to a reference of 75dB (-10dB on dial), and my 22-31PCi at +3dB...

    ...and the plane crash hit 112dB (110dB setting, c weighting, fast response), and the car crash hit 114dB.

    My understanding is that the true dB's are even higher, since the radio shack meter isn't as sensitive with those low frequencies.

    I didn't even try it at full 85dB, because I didn't want to disturb my neighbors too much, since it was almost 9PM.

    I'm holding the meter an arms length away from me, landing right in my viewing spot, pointing toward the ceiling.

    Do these readings sound right? Should I be getting higher dBs? Lower?

    thanks
     
  2. RichardH

    RichardH Supporting Actor

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    What did you calibrate with? (What DVD, method, etc.)
     
  3. Ben Jordan

    Ben Jordan Stunt Coordinator

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    Calibrated with Avia to be 85dB at the 0 point on my dial. Thanks.
     
  4. John F. Palacio

    John F. Palacio Supporting Actor

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    Keep in mind that the compensation figures for the RS meter are frequency specific and are intended to be used with sinusoidal test tones.

    When you use the meter with program material the meter is responding to all the sound, at all frequencies, from all speakers and not the subwoofer alone.

    All that being said, your SPL figures appear to be on the high side.
     
  5. Doug BW

    Doug BW Stunt Coordinator

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    Have you EQed? People can have peaks in their bass response that are upwards of 10dB above the calibrated level.
     
  6. RichardH

    RichardH Supporting Actor

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    Good point, Doug. A big room node could be causing the spike on your meter. Do you have 5 speakers set to small? If so, try your test again, but this time, turn the sub off. Don't change any of the receiver settings, just leave the sub off. Then you can see what your main speakers are peaking at during those scenes.
     
  7. Phil_DC

    Phil_DC Stunt Coordinator

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    Hey Ben,

    Whats the part number for that meter? I tried to get one a RadioShack the other day and they had no clue as to what I was taking about.

    Thanks
     
  8. Doug BW

    Doug BW Stunt Coordinator

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    Phil, the catalog number for the RadioShack SPL meter is 33-2050. Full information maybe found at RadioShack's website, here.
     
  9. Phil_DC

    Phil_DC Stunt Coordinator

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    Thanks Doug!
     
  10. Ben Jordan

    Ben Jordan Stunt Coordinator

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    Doug,

    I don't have any EQ hardware yet, but am very interested in getting something soon. Recommend anything for beginners? Wouldn't want to pay much more than say $300, if that's possible.


    Richard,

    Yes, all set to small. I will try that test again tonight hopefully, exact same settings, except with the sub off, and see what kind of dB's I get, and let you know. Should I perhaps run the test again, with all speakers unplugged, except the sub, and see what it is producing also?

    Thanks guys! Really appreciate your time.
     
  11. Doug BW

    Doug BW Stunt Coordinator

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    Probably the two most popular/inexpensive boxes that people use to EQ their subs are the BFD (Behringer Feedback Destroyer) and the ART 351.

    I have the BFD, which you can get for around $125 delivered on the web. It's a parametric equalizer. It's fairly easy to use, though the ART, being a graphic equalizer, is probably a little more intuitive to use....though you trade off flexibility.
     
  12. Ben Jordan

    Ben Jordan Stunt Coordinator

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    Thanks Doug. I'll pick up a BFD in the next couple of weeks then! Would I need anything else to go with it?
     
  13. RichardH

    RichardH Supporting Actor

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    I don't think it would cause any harm, but it might not be the best idea to run your reciever w/o any speakers. I think doing the "no sub" test should be sufficient to see what's going on.
     
  14. Doug BW

    Doug BW Stunt Coordinator

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    You'll need one additional audio interconnect, an SPL meter (which you already have), and a CD with test tones. Good test tone CDs include the "BassZone Test CD" from www.stryke.com (that has sine waves at 1/6 octave intervals), and "CD 101" from www.autosound2000.com (that has sine waves at 1 hz intervals). Some people have made their own CDs.
    It's also helpful to have a tripod for the SPL meter. And some software to draw pretty graphs of your frequency response. And a spouse who can say with straight face, "Oh yes, that sounds much better now".
     
  15. Ben Jordan

    Ben Jordan Stunt Coordinator

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    Doug,
    Thanks for the info. I was hoping to make my own test tones with the NCH Tone Generator (http://www.nch.com.au/tonegen/), which seems to be able to create some accurate WAV's I could burn. I have a tripod, and a very HT supportive fiance (getting married this Saturday!) who is more than happy to help out. [​IMG]
    Richard,
    I just finished the test with the SVS turned off via its amp switch, and here are my results:
    The airplane crash hit 102dB's at the maximum loud part, with most of it around 98dB's. The car crash hit a maximum of 100dB's, with most of it around 95-96dB's or so. All the same exact settings except for the meter which I put on 100dB and 90dB (ran test twice), instead of 110dB, to get a more accurate reading.
    Do these readings seem correct? I'll run Avia again tonight to verify my levels of 85dB at 0, and 75dB at -10.
    thanks!
     
  16. RichardH

    RichardH Supporting Actor

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    Was your volume knob at -10 like before? If so, I'd say those reading are normal. Full reference level means up to 105 dB peaks at the seats from any 1 channel. So, if you have a few of them going at the same time, it could be a little more. So, if you are running at 10 dB below reference, and a few channels go "full scale", then I think it's reasonable to have 102dB peaks at the seat.

    Truth be told, full reference is pretty dang loud. I think 10dB below w/ the subs a few dB hot is just right for a lot of people and still too loud for some (read: most women).
     
  17. Ben Jordan

    Ben Jordan Stunt Coordinator

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    Yeah, same -10 as before, Richard.
    I agree on the loudness. Although I do love to turn it up to full reference or even a little higher to show off to my friends, if you know what I mean. [​IMG]
    And yes, -10 seems really good for me and my fiance for most movies, if not even a little lower. Gives enough to have a nice full sound, and great effects when they come along.
    Thanks again for your time!
     
  18. RichardH

    RichardH Supporting Actor

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    Sweet, glad it worked out for you!! And a fiance who's supportive of your hobby? Man, make sure to hold onto that one! [​IMG]
     

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