Effects of Humidity on the Velocity of Sound in Air

Measurements have been made of the effects of humidity on the velocity of sound in air at 20.00°C and normal atmospheric pressure in the audio frequency range. The velocity of sound was determined from measurements of the frequency of the decay of normal frequencies of a spherical chamber of very high Q. Contrary to the often-made assumption that the addition of moisture increases the velocity of sound in air, these results show that as moisture is added to dry air the velocity of sound at first decreases. The velocity is minimum at a relative humidity (RH) of about 14%; then it rises. Above about 30% RH, the velocity increases linearly with increasing moisture content.