So imagine if you measure the sound intensity at a certain spot to be $ 72$ deciBels. If you look at the SI-units used in the ratio these are $ \text{W/m}^2$. Does this mean that you can calculate the exact energy transfer per second on a given area, e.g. 2 cm2 to just be the amount of decibells you measure times the area including with the relative intensity?

I would like to calculate the energy transfer of sound.


1 Answer 1


The decibel (dB) is a unit for expressing the ratio between two sound intensities and so has no units.

One decibel equals $10 \log_{10} \left (\dfrac{I_1}{I_2}\right )=20\log_{10} \left (\dfrac{P_1}{P_2}\right )$, where $I_1$ and $I_2$ are the intensity of the two sounds and $P_1$ and $P_2$ are the corresponding amplitudes of the pressure waves.

Examples of sound pressure is a table which illustrates the use of the auditory threshold at $1\,\rm kHz$ as the reference of $0\,\rm dB$ used on many instruments.

You may also find the Wikipedia article Sound Power of interest.

  • $\begingroup$ Thanks for clearing that up. I changed my post. If you use as a reference intensity just atmospheric pressure, how do you calculate the energy exactly? I look at the page but I can't seem to correctly figure it out. Thanks in advance $\endgroup$ Jan 2, 2022 at 8:10
  • 1
    $\begingroup$ @bananenheld It is impossible for a sound wave to have a amplitude equal to atmospheric pressure. Note that a sound wave can be thought of as a variation in pressure about atmospheric pressure. $\endgroup$
    – Farcher
    Jan 2, 2022 at 8:14
  • $\begingroup$ Ok thank you for clearing that mistake up. How can you calculate the energy then? $\endgroup$ Jan 2, 2022 at 9:34
  • $\begingroup$ Sound Intensity and Sound Level $\endgroup$
    – Farcher
    Jan 2, 2022 at 9:53
  • 2
    $\begingroup$ Looking at the "Sound Intensity and Sound Level" table you will see that the reference power per square metre, $10^{-12}$, is 0 dB. So 72 dB is a power per square metre of $10^{72/10} \times 10^{-12} \approx 1.6 \times 10^{-5}$ $\endgroup$
    – Farcher
    Jan 2, 2022 at 10:33

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.