Acoustic Plane Waves

Pressure Plane Waves:

$$\begin{eqnarray*} p^+(n) &\mathrel{\stackrel{\mathrm{\Delta}}{=}}& R_a\,u^{+}(n)\\ p^-(n) &\mathrel{\stackrel{\mathrm{\Delta}}{=}}& -R_a\,u^{-}(n) \end{eqnarray*}$$

where $u^{+},u^{-}$ are
Longitudinal Particle-Velocity Waves

Ohm's Law for Traveling Acoustic Plane Waves:

where

$$\zbox{R_a = \rho c}$$

is the wave impedance of air in terms of mass density $\rho$ ( kg$/$m$^3$ ) and sound speed $c$ .