Drifting Unisons

[Fred S. Sturm]

I guess I wasn't clear in what I wrote. Steinway B's definitely exhibit 
the unison drift phenomenon, and to a pretty marked degree. What I was 
trying to point out was that Steinway B's also have a unique tuning pin 
pattern (well, maybe there are similar ones, but none comes to mind), 
where there is an immense difference in "waste length" on the tuning pin 
side between adjacent unisons. The pins for one unison are set forward, 
right next to the agraffes, next unison set back toward the stretcher, 
alternating throughout the treble section of the piano. If the amount of 
pinblock wood between flange and tuning pin were the major factor in 
making the right string of a unison move farther in pitch than the left, 
wouldn't we see a similar difference between all the strings of one 
unison compared with all the strings of its neighbor? The difference in 
waste length between the left string of C4 and the left string of C#4 is 
greater than the difference between the left string of C4 and the right 
string of C4. 
	
Fred

Newton Hunt wrote:
> 
> When the humidity goes from 15 to 85 percent every year for 10 years
> the pattern becomes quite obvious even on Bs but, as you say, less so
> mostly because the block in so well integrated into the case it's
> movement is restricted.  Small pianos in the S&S line show more of the
> pattern.
> 
> Se, essentially, I beg to differ.
> 
>                 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