At first thought it might seem that the ventilation system in a room
would affect the acoustical properties. The air is the medium that
transmits the sound. It has been shown that the wind has an action
in changing the direction of propagation of sound.[13] Sound is also
reflected and refracted at the boundary of gases that differ in density
and temperature.[14] It is found, however, that the effect of the
usual ventilation currents on the acoustics in an auditorium is small.
The temperature difference between the heated current and the air in
the room is not great enough to affect the sound appreciably, and the
motion of the current is too slow and over too short a distance to
change the action of the sound to any marked extent.[15]
Under special circumstances, the heating and ventilating systems may
prove disadvantageous.[16] A hot stove or a current of hot air in the
center of the room will seriously disturb the action of sound. Any
irregularity in the air currents so that sheets of cold and heated air
fluctuate about the room will also modify the regular action of the
sound and produce confusion. The object to be striven for is to keep
the air in the room as homogeneous and steady as possible. Hot stoves,
radiators, and currents of heated air should be kept near the walls and
out of the center of the room. It is of some small advantage to have
the ventilation current go in the same direction that the sound is to
go, since a wind tends to carry the sound with it.