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Why not just use B rather than dB?

  1. Oct 11, 2014 #1
    Hi,

    My question is very simple but I have not found on google. Why Decibel unit employs Deci?
    I know Deci = 0.1, but why not just use B rather than dB? Is there some historical reason?

    Thank you, enjoyed the forum, it is my first post.
     
  2. jcsd
  3. Oct 11, 2014 #2

    analogdesign

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    The decibel was proposed first, it was originally called the Transmission Unit. The Bel was defined later because it is a straight power ratio.

    http://en.wikipedia.org/wiki/Decibel
     
  4. Oct 11, 2014 #3

    NascentOxygen

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    Hi xorg. http://img96.imageshack.us/img96/5725/red5e5etimes5e5e45e5e25.gif [Broken]

    A bel is the log to base 10 of a power ratio. In practice, if we used bels we'd frequently be relying on a decimal fraction for common measurement comparisons. By using the much smaller measure, decibel, we lift the common measures into integers.

    It's a bit like expressing your height in metres. The all-important part is the fractional bit, but we conventionally tend to pay less heed to that part of a number.
     
    Last edited by a moderator: May 7, 2017
  5. Oct 12, 2014 #4
    Sensitivity of perception is the most natural reason
     
  6. Oct 12, 2014 #5

    NascentOxygen

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    Ah, that reminds me--I've heard it said that a 1decibel step in loudness is about the smallest increment that even the most astute listener can discern. Most of us can perceive a change in sound only if it's at least 2dB. I'm in no position to argue with that figure.
     
    Last edited: Oct 12, 2014
  7. Oct 12, 2014 #6

    Baluncore

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    The neper is more fundamental than the bel. It is the natural log of a power ratio. http://en.wikipedia.org/wiki/Neper

    It is because we use a base 10 number system that we used base 10 logarithms to keep the conversions simple.
    Hence in the days of the slide rule, the bel dominated rather than the neper.

    Somewhere in my collection is some old German calibration equipment for telephone bearers that is calibrated in nepers.
     
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