The Sound pressure reference article from the English Wikipedia on 24-Apr-2004 (provided by Fixed Reference: snapshots of Wikipedia from wikipedia.org)

Sound pressure

Sound pressure p (acoustic pressure) is the measurement in pascals of the average sound wave pressure variations as the sound wave passes by a fixed point.

,

p = sound pressure in Pa = Pascal = N/m²
F = force in Newton N, and A = area in m²

The SI unit is Pascal with the symbol Pa. One Pascal equals a pressure of one Newton per cm²

The amplitude of sound pressure decreases in the free field (direct field) with 1/r of the distance of a point source.

The sound pressure level is calculated in dBs as: L_p = 20 log p₁ / p₀

Reference sound pressure is: p₀ = 2 · 10^-5 Pa = 20 µPa

Sound pressure p in N/m² or Pa is:

Acoustic impedance, sound impedance, or characteristic impedance Z in N·s/m³
Acoustic velocity or sound velocity v in m/s
Acoustic intensity or sound intensity J in W/m²

Notice: The often heard speaking of the "intensity of a sound pressure" is not correct. Think it over.
Use "magnitude", "strength", "amplitude", or "level" instead.

The sound pressure p is connected to particle displacement or particle amplitude ξ in m by:

where:

• acoustic impedance Z in N·s/m³
• sound velocity v in m/s
• frequency f in Hz
• sound pressure p in N/m² = Pa
• angular frequency ω = 2 · π · f

Sound pressure p = ρ · c · ω · ξ = Z · ω · ξ
normally in units of N/m² = Pa.

where:

ρ = rho = density of air

c = speed of sound

ω = angular frequency = 2 · π · f

ξ = particle displacement (particle amplitude)

Z = c · ρ = acoustic impedance (characteristic impedance)

See also: Sound_pressure_level:

External link

• Ohm's law of the acoustics - calculations
• Conversion: sound pressure to sound pressure level and back

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