[pianotech] Plate expansion, was Re: Pitch Change (was: Grey market pianos, seasoned pianos, etc.)

[Marcel Carey]

Hi Wim,

I don't think the plate's struts have much to do with it. If you listen carefully at an out of tune tenor where there are a few wound strings, you usually will find that the wound strings have move much less than the unwound ones. There is the relation with the % breaking factor.

 

And some pianos are much worse than others, which probably has to do with different scaling.

 

But there might be more than one thing that happens that we can't explain. But we can all see what huge humidity swings will do to a pianer.

 

Marcel
 


To: pianotech at ptg.org
Date: Sat, 3 Apr 2010 15:57:49 -0400
From: tnrwim at aol.com
Subject: [pianotech] Plate expansion, was Re: Pitch Change (was: Grey market pianos, seasoned pianos, etc.)


I'm not going to second guess Ric's calculations. I'm not that smart. But something's got to be changing the pitch on pianos between seasons. If it isn't the soundboard going up and down, and I have trouble accepting the concept of the string riding up on the bridge having an effect on tuning, there is only one other factor that could be the culprit, and that is the plate expanding or contracting. If you think about it, where is the greatest change in pitch? I find the biggest change is at the first couple of notes on the treble bridge. On most pianos, that is the longest distance from one end of the plate to the other. If the plate expands from top to bottom, (or front to back on a grand), it wouldn't take much to change the pitch even a few cents. The reason the bass strings, and especially the lowest few, don't change much is because of the big bass strut, which gives the plate more stability. 
 
So perhaps the reason the piano goes out of tune with humidity and temperature has almost nothing to do with the soundboard/bridge moving up and down, but is primarily because the plate is expanding and shrinking. Someone else mentioned something along this line, but it seems have been lost in the conversations. 
 
Has anyone done an experiment or taken measurements of this?
 
Wim  





  		 	   		  
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