 # Sound Pressure

"If a source of sound that produces the same sound level at all frequencies at a given point in the open air is placed in a room, the sound pressure at the same distance from the source no longer will be constant with frequency but will be much higher at the resonant frequencies of the enclosure."
(McGraw-Hill Dictionary of Science & Technical Terms 3rd ed.)

[Acoustics] Fluctuations in air pressure caused by the presence of sound waves. (Hirschorn, Martin; Compendium of Noise Engineering - Part I Sound & Vibration Magazine, July 1987.; Sound & Vibration Magazine, July 1987.)

Sound pressure is the local pressure deviation from the ambient (average, or equilibrium) pressure caused by a sound wave. Sound pressure can be measured using a microphone in air and a hydrophone? in water. The SI unit for sound pressure is the pascal? (symbol: Pa). (Wikipedia)

Sound Pressure Level (Lp)
The ratio, expressed in decibels, of mean square? sound pressure to a reference mean square? pressure which by convention has been selected to be equal to the assumed threshold of hearing.
(Hirschorn, Martin ; Compendium of Noise Engineering - Part I Sound & Vibration Magazine, July 1987. Sound & Vibration Magazine, July 1987.)

Lp = 10 log10(P/Pref)2 = 20 log(P/Pref)

where:
Lp = sound pressure level
P = root mean square? sound pressure
Reference pressure:
Pref = 2 x 10-5 N/m2 = 0.0002 dynes/cm2 =
0.0002 microbars = 20 micropascals (rms)

12.26 - Pressures
Acoustic Levitation
Amplitude
Figure 13.21 - Differential Pressure Zones in Antagonism cause Rotation
Intensity
Sound Absorption Coefficient
Sound Measurements
Sound Power