Drifting Unisons

[Fred S. Sturm]

Newton Hunt wrote:
> 
> > There is a consistent difference between left and right
> > strings, sometimes as much as 20 cents in mid to upper treble
> 
> The pinblock shrinks or expands, gradually, with changes in humidity.
> It can only expand a small amount from left string tuning pin to the
> plate flange, a little more from center string pin to plate flange and
> more from right string pin to plate flange.
> 
> Simple answer but it took me years to understand it as well.
> 
>                 Newton

That might be an adequate explanation except for the fact that Steinway 
model B grands don't show a big difference, if any, between adjacent 
unisons where the tuning pin pattern is offset (bigger difference in 
distance from agraffe to pin from unison to unison than between pins in 
one unison). Also, upright pianos show the same tendency (right tuning 
pin shows more movement), and the distances are reversed from that of 
grands (right pin closest on upright, farthest on grand). 

Regards,
Fred S. Sturm, RPT
University of New Mexico