The Velocity of Sound in Air at Low Pressures

Vacuum response and gas leak detection in piezoelectrically driven sound-resonance cavity

“…When air pressure decreases, both and P will decrease simultaneously; as a result, C air is nearly unchanged with decreasing pressure. 13 However, the change in will also result in a change in the characteristic acoustic impedance of the gas ͑i.e., C air ); and since C air is constant, we have…”