Soundboard Deflection and Pitch Change / was Downbearing

[Ric Brekne]

Actually, I see as a usual rule at least as much fluctuation in the break between tenor and treble sections, and usually see some significant fluctuation in any break  up in the high treble as well.  And in all three places the movement is the same.  In high humidity periods the strings to the right of any break are quite sharp compared to the ones left.   Typically tension on these upper break areas do not vary in the fashion you relate below.... seems like something else is at work....

And I still dont see what exactly is putting all that extra tension on the strings when the humidity rises. 

If it isnt the soundboard deflection... and I cant see that it is... then either the strings themselves react to humidity.... or something is stretching them tighter....  its difficult to think imagine anything else but the iron frame  somehow flexing for some reason in a fashion that might explain this pitch change.... 

Cheers
RicB


At 9:12 am +0200 18/8/06, Ric Brekne wrote:

>..why then does the lower end of the treble behave so differently 
>then the upper end of the tenor.. and likewise with the lower end of 
>the tenor vs upper end of the bass.

Because the tension of the strings is commonly nearest the breaking 
strain in the high singles and the high bichords and furthest from 
the breaking strain in the plain wire strings to the right of the 
break.  The shorter the piano the more these differences are likely 
to be unavoidable and significant.  A string that is at a tension 
well below the maximum (eg. 130lbs. on a #20 wire, as you might 
easily come across on an upright or a less-than-6ft grand) will be 
far more susceptible to changes in humidity and temperature.  Where 
do you get the most fluctuation in pitch on the 5ft grands you tune? 
Almost certainly in the plain wire notes to the right of the break.

JD