"belongs to SOQ-ISO" . "\\(c_g = \\frac{d\\omega}{dk}\\), where \\(\\omega\\) is the angular frequency and \\(k\\) is angular wavenumber."^^ . "Group Speed of Sound"@en . "c" . . . "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." . .