In a dispersive medium sound speed is a function of sound frequency, through the dispersion relation. The spatial and temporal distribution of a propagating disturbance will continually change. The group speed of sound describes the propagation of the disturbance.
Applicable units are those of quantitykind:GroupSpeedOfSound
http://en.wikipedia.org/wiki/Speed_of_sound
In a dispersive medium sound speed is a function of sound frequency, through the dispersion relation. The spatial and temporal distribution of a propagating disturbance will continually change. The group speed of sound describes the propagation of the disturbance.
$c_g = \frac{d\omega}{dk}$, where $\omega$ is the angular frequency and $k$ is angular wavenumber.