Bald Ham Pitch Swing

[Jim Coleman, Sr.]

HI Stan:

The reason the Tenor section moves more than the other sections is because
the bridge has fewer strings per lineal inch to resist the crown rise
effect of the humidity. You will notice that the bridge notchings are 
fanned out more in the midrange. In the high treble the strings are grouped
closer together and are more perpendicular to the bridge. In the Bass
bridge the strings are perpendicular to the bridge, more or less.

You will also notice that the two notes with wound
strings at the bottom of the Tenor bridge do not change as much. This is 
because they are at a much higher tension than the plain wire strings above.

Jim Coleman, Sr.


On Wed, 29 Sep 1999, Stan Kroeker wrote:

> 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
>