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Physics > Sound Pressure

An encyclopedia explanation for the term "sound pressure" is as follows:

"Sound pressure is defined as the difference between the average local pressure of the medium outside of the sound wave in which it is traveling through (at a given point and a given time) and the pressure found within the sound wave itself within that same medium. A square of this difference (i.e. a square of the deviation from the equilibrium pressure) is usually averaged over time and/or space, and a square root of such average is taken to obtain a root mean square (RMS) value."

The table below shows examples of sound pressure and sound pressure levels related to a particular sound source.

Source of sound RMS sound pressure sound pressure level
Pa dB re 20 µPa
Theoretical limit for undistorted sound at 1 atmosphere environmental pressure 101,325 191
1883 Krakatoa eruption   approx 180 at 100 miles
Stun grenades   170-180
rocket launch equipment acoustic tests   approx. 165
threshold of pain 100 134
hearing damage during short-term effect 20 approx. 120
jet engine, 100 m distant 6–200 110–140
jackhammer, 1 m distant / nightclub 2 approx. 100
hearing damage from long-term exposure 0.6 approx. 85
traffic noise on major road, 10 m distant 0.2–0.6 80–90
moving car, 10 m distant 0.02–0.2 60–80
TV set – typical home level, 1 m distant 0.02 approx. 60
normal talking, 1 m distant 0.002–0.02 40–60
very calm room 0.0002–0.0006 20–30
quiet rustling leaves, calm human breathing 0.00006 10
auditory threshold at 2 kHz – undamaged human ears 0.00002 0