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Homework Help: How to calculate audio power level?

  1. Mar 17, 2015 #1
    1. The problem statement, all variables and given/known data

    I am given 5 frequencies but I would like to know how to calculate the power level for both ears just for one of the frequencies (1000Hz) to get a general idea for the rest. In this experiment, we used audio headsets and recorded the voltage and resistance for the left ear and the right ear at the threshold point. It was fun!

    so, for example, at 1000Hz,

    Left ear: Voltage: 1.469
    Resistance: 158,000 (158k)

    Right ear: Voltage: 1.502
    Resistance: 105,000 (105k)

    2. Relevant equations

    I is the intensity

    P is the power

    Screenshot (702).png

    3. The attempt at a solution

    My problem here is that I don't understand what to with this equation. I initially thought to re-arrange it to solve for Power, so


    But then what exactly is Intensity? I really would like to understand and I appreciate any insight that may help me figure this out.
    Last edited: Mar 17, 2015
  2. jcsd
  3. Mar 17, 2015 #2


    User Avatar
    Science Advisor

    If power is in Watts and radius is in metres what is the unit for intensity in the following?


    For your circuit, can/have you solved for the power output from R3? That is what you'll use to find intensity.

    If r wasn't given, you'll have to estimate it. What is this distance? hint: did you use in-ear buds? or over ear cans? (google image these terms if you don't know what they mean)
  4. Mar 17, 2015 #3


    User Avatar

    Staff: Mentor

    The equation you quote deals with the power emitted by a sound source that provides an intensity I uniformly over a spherical surface of radius r. You can think of intensity as the amount of energy per unit area that passes a given location in a unit of time.

    The immediate problem you're dealing with involves the amount of electric power delivered to the headphones (R3). For that you'll need to use equations that pertain to electric circuits. What's your knowledge level there?
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