Sound pressure

The amplitude of sound pressure from a point source decreases in the free field (direct field) proportional to the inverse of the distance from that source. Sound pressure level is a decibel scale based on a reference sound pressure of 20 µPa (micropascals), calculated in dB as:

p₀: Reference sound pressure of 2 × 10^-5 Pa = 20 µPa

Z: acoustic impedance, sound impedance, or characteristic impedance, in Pa·s/m
: v: particle velocity in m/s
: J: acoustic intensity or sound intensity, in W/m²

Sound pressure p:
:
normally in units of N/m² = Pa.

where:
: p: sound pressure, in N/m² = Pa
: f: frequency, in Hz
: ρ: density of air, in kg/m³
: c: speed of sound, in m/s
: v: sound velocity, in m/s
: ω: angular frequency = 2π·f
: ξ: particle displacement (particle amplitude), in m
: Z: acoustic impedance (characteristic impedance) = c · ρ, in Pa·s/m
: a: particle acceleration, in m/s²
: E or w sound energy density, in J/m³
: P_ac sound power or acoustic power, in W
: A area, in m²

Note: The often used term "intensity of sound pressure" is not correct. Use "magnitude", "strength", "amplitude", or "level" instead. "Sound intensity" is sound power per unit area, while "pressure" is a measure of force per unit area. Intensity is not equivalent to pressure.

See also