soundpressure

Sound pressure is the local deviation from ambient atmospheric pressure caused by a sound wave. It is a scalar acoustic quantity measured in pascals (Pa) and varies in time and space as the wave propagates. Instantaneous sound pressure describes the momentary pressure fluctuation, while root mean square (RMS) values are used for steady-state level comparisons.

Sound pressure is commonly expressed logarithmically as sound pressure level (SPL) in decibels: SPL = 20 log10(p/p0), where p is the RMS sound pressure and p0 is a reference pressure (20 micropascals in air). Typical reference points include the threshold of human hearing (~20 µPa, 0 dB SPL), normal conversation (~0.02 Pa, ~60 dB), and levels approaching pain (~20–63 Pa, ~120–130 dB).

Physically, sound pressure relates to particle velocity and acoustic intensity; for a plane progressive wave in a medium of density rho and sound speed c, intensity I = p^2/(rho c). Sound pressure measurements use microphones and pressure transducers, often combined with weighting filters (e.g., A-weighting) to reflect perceived loudness.

Sound pressure is a fundamental parameter in acoustics, audio engineering, environmental noise assessment, and hearing safety. Distinguishing between pressure and level, and using appropriate measurement techniques and reference values, is essential for accurate characterization and control of acoustic environments.