Bald Ham Pitch Swing

[Stan Kroeker]

Apologies for the abbreviated subject line.

Not quite sure I fully understand what is going on when humidity changes
cause pitch fluctuation.  Ya, ya...I know...humidity goes up, soundboard
swells, crown rises, string tensions increase...but... it is always the
lowest tenor strings (10-15 unisons?) which are affected disproportionally
to the rest of the scale.  Many claim that these strings sit on the portion
of the bridge close to the center of the soundboard but the last time I
looked the low end of most tenor bridges was pretty close to the rim.
Almost as close as the bass bridge.  Weird things often happen on either
side of the treble (strut) break as well.

Some pianos exhibit extraordinary pitch swings (a client's Yam GH1 comes to
mind) but none as peculiar as a Baldwin Hamilton (<10 yrs) on which the
entire tenor/treble section fluctuates 25-30 cents each seasonal change.
The bass remains within 5 cents of pitch on this piano.  Is there more to
this phenomenon than the soundboard swells or shrinks?

Regards to all,

Stan Kroeker
Registered Piano Technician