My Weber Duo-Art piano has one oddity related to humidity.  Since it
was fully repinned and partially restrung five years ago, it keeps the
tuning very well within 40-60% relative humidity.  Near 40% and lower,
it gets somewhat out of tune however, but this is not a major problem,
it feels like a "new" piano.

But, the ability to repeat notes fast, especially at low vacuum levels,
drops dramatically when the humidity is near or just over 60%.  The
repetition is "almost tolerable" at around 50%, and good at 40%.  What
could be the reason for this?

It seems that manual playing is a bit sluggish too, when the humidity
is at its highest.  Could it be that the wood swells enough, so that
tight fitted mechanical parts in the hammer mechanics gets too tight?

This problem is a bit annoying, since it limits my piano to work very
well only at around 45% humidity, and obtaining devices to regulate the
humidity that rigidly is just now not an option because of the costs.

Thomas Henden
Oslo, Norway