In response to Robert B. Lang's request [05/06.15 MMD], here is what I
have found.

I moved from stable humidity (Seattle, 55% most of the year) to the
desert near Palm Springs, where the humidity is very low, ranging from
12% to an occasional 30%, according to the weather news on TV.

It took about two years for things to begin to happen.  At first the
upright Marshall & Wendell Ampico began to play with a loss of
expression, then the rewind would not work.  Then the piano would not
play at all.  It turned out that the main bolts holding the stack
together were loose by almost 1/8th inch.  The wood had shrunk and the
stack had gross leaks.

Sitting in the living-room one night, I heard what sounded like a shot
from a small rifle.  It turned out that the ribs on an antique upright
piano had let go.

An antique harmonium had its keys twist so badly that it is not
playable.  Now it looks like the ivory is ready to loosen from the keys.
This was very well built in France about 100 years ago.

When I switched to using a swamp cooler (evaporative cooler) instead of
the air conditioner, things began to normalize with the Ampico, but only
after tightening down many bolts and screws.  The humidity now runs
about 45% to as much as 60%.  The swamp cooler does a good job in
cooling the house also.

Installing a humidifier on the furnace vents did not take care of the
problem.  I don't recommend that type of humidity control.  The better
humidifiers boil the water, but obviously that is not good for the
desert heat, and would be costly.

The Duo-Art has fared much better, although it does require some
adjustments in the zero-level with seasonal changes.  It has been hard
to keep in tune.  Perhaps the greater use of the evaporative cooler will
help when it comes to a stable tuning of the pianos.

I hope this sheds some light on the problems with low humidity.

Bill Chapman
La Quinta, CA