[pianotech] Humidity

[Ron Nossaman]

On 7/24/2012 2:12 PM, Laura Olsen wrote:
> So, how important is it to have a sanctuary at the temperature it's
> used at when you tune the piano?

Not very. The important thing is that the temperature not be changing 
*while* the piano is being tuned. Temperature change, the strings react 
first, pretty much immediately, then the plate catches up later and the 
tuning ends up not far from where it was before the temperature change. 
This has nearly nothing to do with humidity.


> How fast does the wood take on or let go of the humidity?

Much more slowly, as it takes hours, days, for wood to absorb or release 
moisture. The rate is dependent on moisture differences inside and 
outside of the wood. The less the moisture differential, the slower the 
reaction.


>If it was 60% when I tuned it (and 86
> degrees Fahrenheit) and it's only 56% when the A/C is on, how much
> will the piano change in pitch?

Not a lot with only 4% difference, unless it spent a week or three 
months at 25% in between. That's the problem with periodic RH% 
measurements. Wood reaction lags behind the measurements, and the 
measurements don't tell you where it's been in between. Temperature 
means little unless it's changed very recently (hours, minutes). Fact 
is, pitch drift with A/C on/off cycle is noticeable during tuning.

There isn't a high resolution lick and stick simple 25 words or less 
answer. This has been discussed extensively here, and there are some 
excellent and thorough detailed explanations in the archives describing 
the physics of both temperature and humidity effects.

Ron N