Power Levels, Sound Levels And Your Ears

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  • David Meek
    Moderator Emeritus
    • Aug 2000
    • 8938

    Power Levels, Sound Levels And Your Ears

    Hi all. I was reading my latest issue of Home Theater (April 2002) - I know, I know. . . and came across a very interesting article on amplifier power, speaker sensitivity, sound levels and your ears. The full article will eventually be available on their website, but I thought you'd be interested in some info out of it. Of course, all this info is based on an ideal sonic presentation, so in the real world these numbers will probably vary a bit.

    Power vs. Output - speaker sensitivity of 88db - measured at 1 meter:
    1 watt = 88 spl (db)
    2 watts = 91 spl (db)
    4 watts = 94 spl (db)
    8 watts = 97 spl (db)
    16 watts = 100 spl (db)
    32 watts = 103 spl (db)
    64 watts = 106 spl (db)
    128 watts = 109 spl (db)
    256 watts = 112 spl (db)
    512 watts = 115 spl (db)
    1024 watts = 118 spl (db)
    2048 watts = 121 spl (db)
    4096 watts = 124 spl (db)

    Average SPL's:
    Saturn rocket = 194 spl (db)
    Turbojet = 160 spl (db)
    Propeller aircraft = 140 spl (db)
    Threshold of pain = 135 spl (db)
    Riveter = 120 spl (db)
    Movie theater - peak = 105 spl (db)
    Loud voice - shouting = 90 spl (db)
    Conversation = 70 spl (db)
    Quiet residence = 40 spl (db)
    Soft whisper = 30 spl (db)
    Threshold of hearing = 0 spl (db)

    OSHA Sound-level Limits (maximum daily exposure):
    92 spl = 6 hours
    95 spl = 4 hours
    97 spl = 3 hours
    100 spl = 2 hours
    102 spl = 1.5 hours
    105 spl = 1 hours
    110 spl = 0.5 hours
    115 spl = 0.25 hours

    I modified the value for the 95 spl value from 6 hours to 4 to fit the OSHA chart. Also, added "measured at 1 meter".




    David - HTGuide flunky
    Our "Theater"
    Our DVDs on DVD Tracker

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    David - Trigger-happy HTGuide Admin
  • Lex
    Moderator Emeritus
    • Apr 2001
    • 27461

    #2
    I guess that would explain why I find comfortable listening levels posting at less than 90 dB over long periods of extended view/listening.

    Nice post David.

    Lex
    Doug
    "I'm out there Jerry, and I'm loving every minute of it!" - Kramer

    Comment

    • John Holmes
      Moderator Emeritus
      • Aug 2000
      • 2703

      #3
      Good info for sure.

      When I first got into this hobby, attempting to reproduce the theatrical SPL was important to me. As it seemed to make sense that it would yield the directors intent. Now, it is only important that it sounds good to me! And most of the time, that is 12-20 db's or so below reference.

      I'm not sure if my standards changed because of maturing in the hobby or, owning better equipment with proper adjustments made. None the less...lower is better. At least to me.




      "I came here, to chew bubble gum and kickass. And I'm all out of bubble gum!!!" My DVD's
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      Comment

      • P-Dub
        Office Moderator
        • Aug 2000
        • 6766

        #4
        I'll be looking for this article.

        I think the speaker sensitivity is measured at 1 meter. I think you have to add 3db when you have a pair of speakers.

        I actually wonder about some movie theaters around here actually hitting those peaks.

        I read somehwere that the OSHA levels are on the 'A' weighting of a RS SPL meter. Most speaker measurments are done on the 'C' weighting. The diff is that 'A' weithing doesn't take into account some of the lower frequencies.

        I also read somewhere that as we age, our ability to hear the full freqency range decreases. So the highs may be limited as well as the lows. I never thought about the lows, as this is more felt. But apparently there's more of a rolloff down low.




        Paul

        There are three kinds of people in this world; those that can count, and those that can't.
        Paul

        There are three kinds of people in this world; those that can count, and those that can't.

        Comment

        • George Bellefontaine
          Moderator Emeritus
          • Jan 2001
          • 7637

          #5
          Like John, reference is just a little too much for me for most dvds, but there is the odd one that needs to be played close to reference. Most of the time,though, I am around - 12 to -15.




          My Homepage!
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          Comment

          • David Meek
            Moderator Emeritus
            • Aug 2000
            • 8938

            #6
            Originally posted by Paul
            I think the speaker sensitivity is measured at 1 meter.


            Paul, yes it is. Good catch - I'll edit the post to reflect that.




            David - HTGuide flunky
            Our "Theater"
            Our DVDs on DVD Tracker

            .

            David - Trigger-happy HTGuide Admin

            Comment

            • Bruce
              Senior Member
              • Aug 2000
              • 156

              #7
              David,

              OSHA Sound-level Limits (maximum daily exposure):
              This needs to be stated with a qualifier. Therse values are all based on the "A" weighting scale which essentially includes only a subset of the frequency domain, and little to no bass.

              When we calibrate and listen in our HT we do it with a "C" weighting scale, including bass. I think the difference between "A" weighting and "C" weighting can be as much as 10dB at the same volume. The "C" weighted SPL reading is always higher.
              corrected, I agree with Paul


              You can try the experiment with your RS SPL meter sometime by just switching the weighting scale switch and observe the different SPL reading.




              Bruce
              ____________________________________________
              Bruce

              Comment

              • P-Dub
                Office Moderator
                • Aug 2000
                • 6766

                #8
                Originally posted by Bruce
                This needs to be stated with a qualifier. Therse values are all based on the "A" weighting scale which essentially includes only a subset of the frequency domain, and little to no bass.

                When we calibrate and listen in our HT we do it with a "C" weighting scale, including bass. I think the difference between "A" weighting and "C" weighting can be as much as 10dB at the same volume. The "A" weighted SPL reading is always higher.
                I agree. I think the RS SPL meter on "C" goes down to 10 Hz, there's a correction table around as the meter is not that accurate down low. I don't recall off hand where the "A" weighting cuts off.

                However, I have noticed when I switch between the two, there's a drop in dB from the "C" to the "A" and not the other way around. I have found to get higher reading on the "C" weighting, which is what I would expect.

                Reference level is really to help balance your speaker levels. Enjoyable listening levels are a personsal preference.

                Reproduction of LFE ie under 100Hz is where you really need the power.




                Paul

                There are three kinds of people in this world; those that can count, and those that can't.
                Paul

                There are three kinds of people in this world; those that can count, and those that can't.

                Comment

                • P-Dub
                  Office Moderator
                  • Aug 2000
                  • 6766

                  #9
                  Just to follow up on this speaker sensitivity and watt table. Another important formula/rule is that sound decreases by the square of the distance from the source. Or for every doubling of distance, dB drops by 6 dB.

                  So a formula I have entered into my spreadsheet goes something like this. dB(seat)= dB(ref)-20*Log(D(seat)/D(ref))

                  Where:
                  dB(seat)is the dB in my sweat spot
                  dB(ref) is the measured dB at 3ft
                  D(seat) is the distance in feet from speaker ref to seat
                  D(ref) is the distance in feet from speaker to db(ref) measurment, ie 3 ft

                  What does this all mean? Well for my set of 91db speakers the chart at 1M, or 3ft, would read as follows:
                  eXL16

                  1 watt = 91 spl (db)
                  2 watts = 94 spl (db)
                  4 watts = 97 spl (db)
                  8 watts = 100 spl (db)
                  16 watts = 103 spl (db)
                  32 watts = 106 spl (db)
                  64 watts = 109 spl (db)
                  128 watts = 112 spl (db)
                  256 watts = 115 spl (db)

                  Adjusted spl levels at my seat 12 feet away is:

                  1 watt = 79 spl (db)
                  2 watts = 82 spl (db)
                  4 watts = 85 spl (db)
                  8 watts = 88 spl (db)
                  16 watts = 91 spl (db)
                  32 watts = 94 spl (db)
                  64 watts = 97 spl (db)
                  128 watts = 100 spl (db)
                  256 watts = 103 spl (db)

                  I also recall that if you have two speakers, you need to add 3db to these numbers. And this is all in one of those sound deadend rooms, which we all have.
                  Paul

                  There are three kinds of people in this world; those that can count, and those that can't.

                  Comment

                  • JonMarsh
                    Mad Max Moderator
                    • Aug 2000
                    • 15272

                    #10
                    Then, let's also consider real world speaker sensitivity.

                    Most two or three way's, with adequate baffle step compensation (another story and article just in that one) will be lucky to crack 85 dB sensitivity. A number of highly rated commerical speakers (think Joseseph Audio, Magneplanar) are realistically in the 83 dB/watt area.

                    Then there are the big boys, like the X1, at a genuine 93 dB/watt.

                    So, your reciever is good for 100 watts per channel, two out of five driven? :roll: (I have a tinsy bit of a problem with a lot of HT recievers and some amps).

                    Nonetheless, being safe with SPL exposure is a good idea- this coming from an ex rock and roller that spent more than a few hours in front of a Marshall stack...if you know what that is.

                    Foam ear plugs. Always use 'em for live sound- including as a concert goer.

                    The odd thing is, with a "poorer" system you're less likely to "overdrive" your ears, because you'll get more feedback from rising distortion levels and general strain. The "dangerous" systems are the ones that will kick butt and sound utterly clean doing it. Also, the ear appears to be a lot more sensitive to damage in the 250 Hz to 5 kHz region. Probably something to do with inner ear bone resonant frequencies.

                    Those distance curves get modified depending on the type of speaker; line sources and speakers like Magnepans don't behave as a point source, and fall off slower- which I think is nice, because the volume distribution with distance is more even.

                    Regards,

                    Jon




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