Sound pressure

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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:

Reference sound pressure is: p₀ = 2 × 10^-5 Pa = 20 ÃÂµPa

Sound pressure p in N/m² or Pa is:

Z: Acoustic impedance, sound impedance, or characteristic impedance, in N-s/m³

v: Acoustic velocity or sound velocity, in m/s

J: Acoustic intensity or sound intensity, 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. "Intensity" is a the sound energy value, but "pressure" is a sound field value. Intensity is not pressure.

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

where:

Z: acoustic impedance, in N-s/m³

v: sound velocity, in m/s

f: frequency in Hz

p: sound pressure, in N/m² = Pa

ω: angular frequency = 2π f

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

where:

ρ: density of air

c: speed of sound

ω: angular frequency, = 2π · f

ξ: particle displacement (particle amplitude)

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

Sound pressure

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