A special case of specific impedance is characteristic acoustic impedance Z 0, which is designated as the wave resistance of the medium.
Z 0 is the quotient of the sound pressure and the sound particle velocity in a plane wave and, neglecting the damping in the medium, is the product of the material parameters speed of sound c and density ρ:
Wave resistance Z 0 links the sound pressure and sound particle velocity in the same way as the voltage and current are linked by the Ohmic resistance in Ohm's law.