Helikajarõhu

Helikajarõhu (Estonian for sound pressure) is the instantaneous pressure variation in air caused by a propagating sound wave. It represents the deviation of the local air pressure from ambient atmospheric pressure and is proportional to the amplitude of the acoustic wave. The concept is central to describing the strength and perception of sound.

Measurement and units: Helikajarõhu is measured in pascals (Pa). The commonly used quantity is the sound pressure level (SPL), defined as SPL = 20 log10(p_rms / p0), where p_rms is the root-mean-square pressure and p0 = 20 µPa is the typical reference in air.

Relation to intensity and distance: The time-averaged acoustic intensity I relates to p_rms by I = p_rms^2 / (ρ c), with ρ the air density and c the speed of sound. In free space, for a point source, pressure amplitude typically falls approximately as 1/r, and doubling the distance reduces SPL by about 6 dB.

Applications: Helikajarõhu is used in architectural acoustics, noise control, audio engineering, occupational safety, and environmental noise assessments. It is distinct from sound power, which measures total energy emitted regardless of distance.

See also: acoustics, decibel, sound pressure level, impedance.