I'm looking into a way to calculate the pressure by which a sound wave at close proximity to the target object impacts. My research led me to this physics site (http://hyperphysics.phy-astr.gsu.edu/hbase/Sound/intens.html), and it shows the pressure relative to hearing. Is this valid or other means is available.

  • $\begingroup$ Pressure is force/area and does not need to be referenced to the threshold of human hearing. This is something we do in musical acoustics and other aero-acoustics studies when going to the log scale. In the log scale (dB) you must have a reference pressure. Underwater acoustics uses a different reference so looking up SPL values in one table will not translate to other measurements. You can use any ref you want but must be consistent and understand what they mean. $\endgroup$
    – user196418
    May 13, 2019 at 12:12

1 Answer 1


Is this valid or other means is available.

It is valid for most use cases. Typically sound pressure is referenced against the hearing threshold pressure which is defined as $p_0=20e^{-6}Pa$. Intensity is defined as the product of pressure and particle velocity. In free air these are related by the free field impedance of air which is the product of density and speed of sound. Both are dependent on static pressure and temperature but in normal conditions it's about $413Ns/m^3$. If you plug in the numbers, the resulting intensity becomes $I_0=0.96e^{-12}W/m^2$ so it's very close.

However that only holds in free air and is not valid if you are close to a sound source or a reflecting surface.

  • $\begingroup$ What happens when you're so close to the sound source? I assume the closer the target is to the sound source, the more energy/pressure it receives before the sound diffuses too far out. I'll like to maximize the amount of pressure the target receives from the source. $\endgroup$
    – TechDroid
    May 10, 2019 at 20:22
  • 1
    $\begingroup$ Close to the source you see the impedance of the source which typically includes a large reactive component. If you want to measure the intensity you need to measure both velocity and pressure. If you just want the pressure, use a pressure microphone. If you just want the velocity, use a velocity microphone. $\endgroup$
    – Hilmar
    May 11, 2019 at 13:04

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