Particle displacement or displacement amplitude is a measurement of distance of the movement of a sound particle from its equilibrium position in a medium as it transmits a sound wave.
[1] The SI unit of particle displacement is the metre (m).
In the case of a sound wave travelling through air, the particle displacement is evident in the oscillations of air molecules with, and against, the direction in which the sound wave is travelling.
The particle displacement of a progressive sine wave is given by where It follows that the particle velocity and the sound pressure along the direction of propagation of the sound wave x are given by where Taking the Laplace transforms of v and p with respect to time yields Since
, the amplitude of the specific acoustic impedance is given by Consequently, the amplitude of the particle displacement is related to those of the particle velocity and the sound pressure by Related Reading: