Posted by John Swensen on February 15, 2002 at 12:52:31:
In Reply to: Effect of temperature on tuning posted by Doug on February 14, 2002 at 22:15:18:
As Art H. has pointed out, the speed of sound in air rises with temperature, effectively making wind instruments sharper as they warm up. It is true that the metal (or, to a much less extent, wood, for instruments like serpents) expands with heat, physically lengthening the horn and tending to flatten it, the lengthening effect is much less than the increase in the speed of sound, so wind instruments go sharp, overall.
For tiny instruments, like piccolos, the flow of warm air pretty quickly warms the entire air column, whereas, for huge instruments like tubas, the leadpipe will warm up quickly, but the bell probably will never get above the ambient temperature. Therefore, piccolos and small instruments go from flat to sharp very quickly as they are played, and tend to have their pitch controlled by the player's breath temperature, while tubas have their pitch controlled, much more, by the room temperature.
For violins and similar instruments, both the wooden neck and the steel strings expand as they warm up, but the steel strings expand far more than the wood, so they tend to go slack and flat as temperature rises.
Pack an 80-piece orchestra onto a cold stage, turn on the hot stage lights, and the strings and winds will diverge in intonation with time, winds going sharp, strings going flat.