The phase speed of a sound wave in a compressible fluid if the expansions and compression are assumed to be adiabatic. This speed a is given by the formula

a^{2}= (c_{p}/c_{v}) RT

where c_{p} and c_{v} are the specific heats at constant
pressure and volume, respectively; R is gas constant; and T is the Kelvin
temperature. The value of this speed under standard conditions in dry air is
331 meters per second. Compare Newtonian speed of sound.