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
Source of sound	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