[pianotech] pitch and temperature

[Paul McCloud]

Hi, Gene:
    Remembering my school days, the only way to predict changes is to test empirically and then make an educated guess (theory) about what will happen in a new situation
    If you change the temperature around a piano, the relative humidity is affected as well as the strings.  If you raise the temperature, the relative humidity goes down.  In course of time, the wood will shrink and affect the tension of the strings.  The temperature of the strings also affects pitch.  If you raise the temperature, the string tension goes down, pitch goes flat.  
    Exactly how much change would best be estimated by taking a measurement  with a ETD or frequency counter and then vary  the surrounding temperature  One would  have to test many different pianos to see exactly how much the pitch would change for a given temperature change.  One would have to wait a sufficient amount of time for the change to take place, given that wood takes time to adjust to a new relative humidity level.  Also, remember that humidity changes affect the registers differently, so that we see larger pitch changes in the low tenor when the weather changes.  That's where the tension is usually lower as a percentage of breaking point.  Predicting how much the  pitch may change may or may not help you because likely the changes are going to depend upon which section of the piano you're referring to.
    Another factor is that different kinds of heat sources make this kind of testing difficult.  Suppose you have a stage where the ambient temperature is 70 degrees.  Then you turn on those hot stage lights.  The ambient temperature isn't going to change that much, but the piano will heat up and throw the tuning out the window.  Instead of taking a thermometer and testing the ambient temperature, you'd have to measure the temperature of the strings.  You would need to set up a repeatable test to determine how much pitch changes with a given temperature change, adjusted over time.  Given the different types, sizes, makes, environments of pianos and venues, making a prediction of any accuracy might be a very challenging effort.  
    Best of luck.
    Paul McCloud
    San DIego


----- Original Message ----- 
From: Gene Nelson 
To: pianotech at ptg.org
Sent: 01/09/2011 12:29:09 PM 
Subject: [pianotech] pitch and temperature


Curious if anyone knows of a reasonably accurate method to predict pitch change in a piano based on temperature change?
Gene Nelson
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