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Sound pressure

Sound pressure: Encyclopedia - Sound pressure

Sound pressure p (or acoustic pressure) is the measurement in pascals of the root mean square (RMS) pressure deviation (from atmospheric pressure) caused by a sound wave passing through a fixed point. The symbol for pressure is the lower case p. The upper case P is the symbol for power. This is often misprinted. The unit is pascal (symbol: Pa) and that is equal to a force (F) of one newton (1 N) applied ov ...

Sound pressure

Sound pressure: Encyclopedia - Sound pressure

Sound pressure

Sound pressure p (or acoustic pressure) is the measurement in pascals of the root mean square (RMS) pressure deviation (from atmospheric pressure) caused by a sound wave passing through a fixed point. The symbol for pressure is the lower case p. The upper case P is the symbol for power. This is often misprinted. The unit is pascal (symbol: Pa) and that is equal to a force (F) of one newton (1 N) applied over an area (A) of one square metre (1 m²).

The amplitude of sound pressure from a point source decreases in the free field (direct field) proportional to the inverse of the distance r from that source. That is 1/r and really not squared!
Sound pressure level is a decibel scale based on a reference sound pressure of 20 µPa (micropascals), calculated in dB as:

This is written "dBSPL".

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

Sound pressure p in N/m² or Pa is:

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

Sound pressure p is connected to particle displacement (or particle amplitude) ξ m, by:

Sound pressure p:

normally in units of pacals.

where:

The distance law for the sound pressure p is inverse-proportional to the distance r of a punctual sound source. This is not an the inverse-square law that is applicable to sound intensity.

(proportional)

Note: The often used term "intensity of sound pressure" is nonsensical. 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.