Flat Facts

[Ron Berry]

Dear Mystery writer.  The soundboard has a crown which makes it higher in 
the center.  When the humidity goes up the wood expands and it can get 
bigger sideways because it is constrained by the rim.  So it moves up adding 
more crown.  This raises the bridge and since the strings are held by the 
plate this puts more tension on them thus raising pitch.  The inverse 
happens when the humidity goes down.  Some piano seem to go up and 
down along the whole scale better than others.  

I find the the last plain wires at the tenor break are the most prone to 
change.  I believe this is because they are stretched to a very low percent of 
their breaking point which makes a small change in tension have a bigger 
affect on pitch.  The wound strings next to them, even if they are on the 
tenor bridge stay in tune much better because they are at a higher percent 
of the breaking point.  

Also it may be that the soundboard is more flexible in the middle and that 
affects the tuning stability also.  Bad scaling makes this worse.  The worst 
example I can think of is the Yamaha GH-1.  This piano goes radically out 
when the weather changes and it is because the break is clear down at B2 
which is very low for such a small piano.

As far a you writing as a mystery writer, I have always felt that the only 
stupid question is the one you didn't ask.  The whole point of a list like this is 
to help pass information along to others not to prove how smart we are.  
Most of us who have been around for a while only have this information 
because someone else was there to answer our "stupid" questions.

Ron Berry


On 26 Mar 2005 at 11:49, Alan wrote:

> 
> This question is so basic and naive, I fear the wrath of the list so I will ask it annonymously ...
> 
> Customer asked: "I understand that humidity change is the principle cause for going out of tune, 
> but if it gets flat than sharp, etc., why is the long term trend always flat? In other words, if it's a fact 
> that the tuning pins are slowly turning counterclockwise with playing and weather, why can't you 
> just lock them in place, somehow,so the piano stays close to pitch all the time?"
> 
> I stood there staring stupidly and could not conjur a sensible-soundinganswer.
> 
> What would YOU say?
> 
> Mystery Writer
> Salem, MO
> 
> 
> --
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Ron Berry, RPT, Indianapolis, IN
ronberry@iquest.net
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