In the violin, the fundamental air cavity mode (the A0 mode) is associated with the sound radiated by the f-holes. The dependences of the sound velocity of the A0 frequency on gaseous temperature and mass were investigated. It was found that the frequency of the A0 mode changed, depending on the molecular weight and the temperature of the gas filling the violin's body. From these results, it was deduced that a temperature change in the room in which musical instruments are played may be reflected in their tones. The measurement of the A0 modal frequency of a violin, focusing on the molecular weight and temperature of the gas, would be useful to students of physics to help in the understanding of sound velocity.