Scotty Greene asked about the shift in pitch in pianos and organs
which occurs with a temperature change.  In pianos, the effect is
transient: with cooling temperature, the strings contract in length
raising their pitch.

The amount of pitch change is different throughout the piano, with
the largest differential change occurring at the transition between
the bass and the tenor strings where a discontinuity of 14 cents is
typical on a 6-foot grand piano with a 10-degree Fahrenheit temperature
shift.  When the cast iron plate catches up with the string temperature
(24 to 36 hours later) the piano will be back in tune with itself and
the world (if it was so before the temperature shift!).

With pipe organs, as with all air-column instruments, the pitch
drops with decreasing temperature.  The effect is quite pronounced
as the shift is 1.7 cents per degree Fahrenheit (3 cents per degree
Centigrade).  In our church in winter, the organ pipes at the
sanctuary ceiling warm to near 90 degrees when the heat comes on,
raising their nominal pitch some 34 cents.

However, the air source for the organ chest is drawn from the unheated
attic space in which the air temperature can be in the range of 30 to
40 degrees.  The pipes cool at different rates depending on how often
they are played during the music, and whether they are metal or wood,
stopped or open.  You can imagine the effect!

I have concluded that pipe organs should reside only in 300-year-old
unheated cathedrals with 6-foot thick stone walls.

John Rhodes - RPT
Vancouver, Washington

P.S.:  The MMD Technical Archives have a good tutorial by Johan
Liljencrants at  http://www.mmdigest.com/Tech/soundspeed.html