[CAUT] Humidity, Bridge caps, pitch drift

[Ed Sutton]

Re: [CAUT] Humidity, Bridge caps, pitch driftI wish that someone would make a direct measurement of the supposed rise of the soundboard, and of the supposed bridge roll.
I also wish there was a way to stabilize the soundboard so we could find out if humidity causes a swelling of the bridge cap sufficient to explain the pitch change. Or perhaps build a piano with a plexglas soundboard and wooden bridge, and another with a wood soundboard and a solid plastic bridge.

For example, I am dealing with a piano with a full, enclosed climate control system underneath, and it continues to have fast responses to ambient humidity changes.  I'm wishing I could install tiny heater bars all along the bridges to see what happens.

And I realize that anything we prove about one piano may have no relation to another piano.

Ed S.
  ----- Original Message ----- 
  From: Shelley 
  To: Ed Sutton , caut at ptg.org 
  Sent: Monday, June 29, 2009 10:11 PM
  Subject: Re: [CAUT] Humidity, Bridge caps, pitch drift


  Hi Ed,

  When I worked in Seattle with Darrell Fandrich, if I recall correctly, he opined that there is some amount of bridge roll due to the rise of the soundboard, some models being more likely to have the effect that you've described.  I see it all of the time here in the summer especially on less expensive pianos.  But, somewhat of a difference in the left strings even in the best pianos if they are in the rather wet conditions naturally occurring in the summers.

  One can picture in our minds eye that the soundboard has no where else to go, being held solid on all of its outer diameter, so it will variably rise, and the plate struts seem to have more flex. (yes/no?)  Either Darrell or Del would give the best explanation, I believe.

  See you in Grand Rapids!  

  Shelley




  On 6/26/09 7:43 PM, "Ed  Sutton" <ed440 at mindspring.com> wrote:


    Here's the pattern I saw on a 5'2' grand piano:

    On the long bridge, in each section, the leftward bridge notches terminate the speaking length in the middle of the bridge. As the scale ascends, the notches progress toward the front of the bridge. Crossing the gap at the plate strut, the notches start again at the middle of the bridge, and step forward again to the front edge. At the next strut, the same thing happens.

    The piano was humidity struck. At the leftward end of each section, where the strings terminate at the center of the bridge, pitch was 10-15 cents sharp. As the scale progressed toward the front of the bridge, the pitch drift became less, and was almost at pitch as the notches came close to the front edge.

    This pattern was repeated in each section.

    Why?

    Ed S 




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