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What do I need to know about Decibels?

Discussion in 'Miscellaneous [BG]' started by MicRidley, Feb 21, 2016.

  1. Hey forum-lurkers,

    I shamefully admit that I am pretty oblivious as to exactly what Decibels are and what I should know about them to be a half decent bassist.

    Sure all of my amps have had the mystical db on them.

    But it wasn't until my relative received one of our grandfather's old gigging amps with a -10 db plug in and a dozen different obscure dials on it that I realized how clueless I am.

    Someone in the past just told me it is "loudness", and I've just fiddled with knobs until the mid/high/lows have sounded right to me.

    Now, I was recently also told that you have to know your equipment in and out.. Since " db" is all over my amps, I figured that's a part of it.

    Feel free to treat this as a "for dummies" because I'm sure it isn't so complicated for many other people.

    Thanks in advance,

  2. dB stands for deciBel. Measurement of audio volume invented by Alexander Graham Bell.
    I know a couple things about them: 1. Every 10 additional dB is a doubling of the volume; i.e., 60 dB is twice as loud as 50 dB.
    2. Jetliner engines up close are 110 dB or so, and crash cymbals when struck are about 100.
  3. hrodbert696

    hrodbert696 Moderator Staff Member Supporting Member

    What confuses me is that the same term is used for sound volume but also for electrical signals before they have been translated into actual sound by a speaker. If you run a signal with the same dB into a 6" speaker and a 15" speaker, all other things being equal, does it come out of the bigger speaker louder? If so, should there be some other term than dB for the electrical signal itself?

    For actual sound volume, here's a handy guide - Decibel (Loudness) Comparison Chart

    Or a picture for people who don't want to follow a link:
  4. RED J

    RED J Lol

    Jan 23, 2000
    Politician sounds really good at about 120.
  5. GIBrat51

    GIBrat51 Innocent as the day is long Supporting Member

    Mar 5, 2013
    Lost Wages, Nevada
    They sound a whole lot better at about 5, IMO... Buddy Holly/Eddie Cochran, on the other hand...:thumbsup::thumbsup:
    Gravedigger Dav likes this.
  6. JohnMCA72


    Feb 4, 2009
    A decibel (dB) is the ratio of one quantity relative to another. It's expressed on a logarithmic scale to keep the numbers manageable. The suffix tells you what the reference is that is being compared against. "SPL" is a suffix that means "Sound Pressure Level" & is what the chart posted by hrodbert696 shows. Using a logarithmic scale is more convenient than a linear scale when dealing with values that double again & again over the useful measurement range.

    dBSPL = 20 * log(P1/P2)

    Example: P1 = 20 Pa (threshold of pain) & P2 = 0.0002 Pa (threshold of audibility)

    dBSPL = 20 * log(20/0.00002)
    dBSPL= 20 * log(1000000)
    dBSPL = 20 * 6
    dBSPL = 120 which, according to the chart, is the threshold of pain.

    Remember when you were sitting in school, in math class, thinking, "I'm never going to need this $***!"? This is part of what you thought you'd never need. It's a shame they didn't make it more interesting back then.
    hrodbert696 likes this.
  7. Gravedigger Dav

    Gravedigger Dav Supporting Member

    Mar 13, 2014
    Fort Worth, Texas
    I thought Decibel was Clarabell's sidekick
    hrodbert696 likes this.
  8. silky smoove

    silky smoove Supporting Member

    May 19, 2004
    Seattle, WA
    Don't forget about dbV, dbU, dbfs, dbRMS, and more importantly how they all relate to one another.

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