Seasonal pitch change:

[David Love]

Even so called "equal tension" scales are not really equal tension as there
are variations within each gauge section.  I would imagine there are a
confluence of factors: case, soundboard, bridge, plate expansion and
contraction, friction, scale tension/break point variability.
Interestingly, even 100 years ago in the discussions of the major
manufacturers of the day catalogued in "Piano Tone Building" edited by Del
Fandrich, there is reference to string tension as a factor in tuning
stability.  Let me know when you figure it out though.  As Bill Ballard is
fond of quoting: "I gotta go to woik".

David Love
davidlovepianos at comcast.net 
www.davidlovepianos.com

-----Original Message-----
From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf
Of RicB
Sent: Sunday, March 11, 2007 4:19 AM
To: pianotech at ptg.org
Subject: Seasonal pitch change:

As I have shown, this lower tension thing... which is really lower % of 
breaking strength (which in itself turns out to be a rather dubious term 
in practice) doesnt really account for the large  differences / 
uneveness in pitch change through out the scale.   Tho no doubt it plays 
what can be called a significant roll. I'm working on a combination of a 
basic scaling spreadsheet and the deflection / tension changes 
spreadsheet along with this last bit about pin angles and strings 
climbing them (which I am glad to see finnally acknowledged) to show the 
isolated effect of such changes on real scales.  I think one will see a 
suprising picture develop, and one that very much deviates from what we 
observe.  Which means that other quite significant forces (for not to 
say dominant) are at work, which to some degree must counter act and to 
some degree work in concert these weve been discussing.

I dont know of any data at all that supports the claim that scales 
designed with more equal tension through the piano will tend to go out 
of tune more evenly.  Is this casual observation based or can you point 
me to some specific study ?

Cheers
RicB


    The lower the tension in a given string the greater the change in
    pitch for
    a given change in length.  Since the lowest tension tends to be in
    the low
    tenor, that is where the largest change in pitch generally is.  The bass
    section is usually the highest string tension and therefore changes the
    least.  On many pianos the scale tensions also drop in the upper treble.
    Scales that are designed with more equal tension through the piano
    will tend
    to go out of tune more evenly.  


    David Love
    davidlovepianos at comcast.net
    www.davidlovepianos.com