[CAUT] Wire Stretch

[RicB]

Hi Bob

My point was simply that if the idea of figuring a scale was to some how 
evenly compensate for the soundboard / bridge assembly's reaction to 
climate changes... then it strikes me that this would require a uniform 
amount of downwards pressure on the board from the string plane over the 
entire scale.

I'm assuming that  wood responds dimensionally  more or less evenly to 
climatic changes. If said climate change caused a 1 mm change in string 
deflection for example... then a very uneven change in string tension 
will result unless the resisting force of the strings to being deflected 
in the first place was even.

This thought was in response to the following quote. 

        " It is now known from experience that practical equality of
        tension throughout the instrument tends to prevent changes in
        the tuning due to variations in the temperature.  When the
        tension is equal the temperature movements are equal"

I still dont see how equality of tension itself will work contribute to 
an instruments stability in the face of climatic variations. Tho as I 
said... I am quite the novice when it comes to all that relates to 
scaling.  I will of course eagerly read the 1999 articles to get a 
better understanding of your point here below... which strikes me as 
interesting right off the bat.

Cheers
RicB

Bob Hohf writes:

    Why would you ever want to set the same downbearing force per unison
    when
    the unisons are so unevenly distributed along the length of the bridges?
    The top two sections of a typical concert grand contain 43% of the
    strings
    on 20% of the total bridge length.  A smaller piano may have 46% of the
    strings on 29% of the bridge.  Setting a uniform downbearing per
    string will
    set up a tone-stifling imbalance in the downbearing force along the
    bridges.
    For 20+ years I have been setting downbearing on the principle of
    uniform
    force per unit of bridge length.  This produces much less force per
    string
    in the high treble and much more in the tenor.  I don't measure
    angles.  In
    Parts 5 & 6 of "Recapping Bridges" in the 1999 Journal, I present a
    discussion of downbearing as force, not dimension, and describe a
    method of
    setting a more uniform load distribution.  I'm sorry it's too
    involved to go
    into detail here.  I know of one other rebuilder besides me who does
    something along these lines.

     

    Bob Hohf

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