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B Can someone explain to me these equations of sound waves?

  1. Mar 25, 2017 #1
    I = 1/2 ρ v ω2 A2

    I don't know what "I" is nor do I know what "A" is but it has to do with sound waves.
    May you also please correct me if I am wrong but is:
    ρ = density of air
    v = velocity of sound = 343 m/s
    ω = angular frequency of the sound wave = 2πƒ

    And also may you please answer what is this second equation?:

    β = 10dB* log(I/I0) ?
    Last edited by a moderator: Mar 25, 2017
  2. jcsd
  3. Mar 25, 2017 #2


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    Staff: Mentor

    I looks to be the sound Intensity. The last equation looks to be the change in Intensity in dB as the sound wave propagates...

    Can you post links to where you got the equations from?
  4. Mar 25, 2017 #3
    Do a dimensional analysis.You may find a (time)^-3 term, which is a hint. Just as a wild guess, try units for area for A... then look up the dimensions for power.
    Quite often, power ratios are expressed as a logarithm.
  5. Mar 25, 2017 #4


    Staff: Mentor

    ##\omega## stands for angular frequency which is ##= 2 \pi f## where f ins the frequency.
    ##I## stands for intensity which is ##= power/area##
    ##\beta## stands for decibel level which is a relative loudness

    This Rutgers lab gets into db measurements and describes the last equation in your post that converts sound intensity relative to a standard baseline intensity to decibels:


    The HyperPhysics book has a description of these equations in great detail:

    Last edited: Mar 25, 2017
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