Long term pitch drop, was: Type O

[RicB]

I also have made some atttempts at calculations regarding to vertical 
displacement of a string and the kinds of tension (and hence) frequency 
changes various degrees of said would cause.  The basic proceedure for 
calculation was verified by Dr Alexander Galembo... so I suppose its 
reasonably safe as a pointer.  If you were to apply then entire change 
in string tension to the speaking length only (which of course doesnt 
really happen)... but even then.... giving the speaking length the 
entire benifit of the doubt as it were.... it would take gargantuan 
vertical displacements to cause any significant pitch change.  It just 
cant be.  Pitch rises of 50 cents would crush a soundboard under the 
required increased downbearing force that results.  In the highest 
treble you might find some hearable change due to some climate related 
vertical rise and drop of the soundboard.... but I just dont see it 
happening.

I rather have the feeling that the soundboard may be attempting to 
change its vertical orientation and because of the curvature of both the 
soundboards horizontal plane and the curve of the bridge the whole 
assembly may be twisting... rocking a bit.  In anycase... since vertical 
rise or fall of the soundboard just doesnt seem reasonable as an 
explanation... then a slight change in string length due to the bridge's 
leading edge moving 1 mm forward due to a slight rolling of the bridge 
caused by an increased straining against downbearing.  This is all 
purely speculation on my part at this point. But it would also on the 
surface of it perhaps explain a bit better why section crossovers 
experience such different pitch changes.  Dog legs and bridge endpoints 
would represent weaker spots as it were.

I would further speculate that a soundboard built on the RC&S idea may 
actually be more somewhat more stable if the above has any truth to it. 
I do not see what an epoxy laminated veneer bridge cap would effect 
stability... tho I do see why it might help avoid self-beating strings.

Cheers
RicB


    I don't have one to evaluate - but - soundboard rise and fall,
    according to the admittedly crude calculations I'm capable of,
    have very little to do with the observable pitch changes we
    can easily enough measure in pianos, so if the bridges and pin
    block are of a "standard" configuration, I wouldn't expect
    them to be significantly more stable.

    I have observed, and verified second hand from the keepers of
    pianos I've done for others, that epoxy laminated veneer
    bridge caps have a positive effect on both tuning stability
    and false beat elimination.
    Ron N