[pianotech] Humidity

[Encore Pianos]

Allow me to illustrate Ron's point about the temperature being the greater
culprit than the humidity:

I tune for an old Congregational Church here in New Hampshire - no
insulation in the walls, old funky windows.  They decided to stop heating
the building during the week when no one was around when oil prices went
insane a few years ago.  January tunings were always an exercise in
futility.  The music director would come over a couple of hours before my
scheduled arrival and turn on the heat.  It's morning, so it might be 0 or
10 degrees outside, and not far north of that inside.  It's up to about 55
when I walk in the door, and will be 65 or up by the time I finish (give up
on) the tuning.   The piano's as cold as a frozen ham in a walkin freezer,
and the plate and sides of the piano start sweating as the condensation
forms due to the temperature differential between the piano mass and the
air.  Typically, I would chase my tail for about 2 hours, doing 3 or 4
passes on the piano.  As I get one end the piano in tune, the other end has
already shifted.  And so on until I give up.  After a few years of these
chronic psychotic episodes,  I refused to tune the piano during the winter
months.

It could be argued that taking that cold air of 20 degrees F. and
superheating it up to 70, will cause the relative humidity to drop
considerably and that would be true.  But I am talking about quantified
pitch changes of 10 cents or more within 10 or 15 minutes for a given note.
There simply isn't enough time for humidity (or lack thereof) to work it's
wonders on the piano.

In contrast, the temperature has changed substantially over a fairly short
period of time.  Probably the thing that changes the most is the piano wire
itself because it is far and away the smallest thermal mass.  The soundboard
would respond to the temperature more slowly, and the rim more slowly still.
All are moving, but not at the same rate.  All are culprits, but the wire is
the greatest.   It likely would be a number of hours before all reached an
equilibrium, and I don't have that much patience or time.  

Will Truitt

-----Original Message-----
From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf
Of Ron Nossaman
Sent: Tuesday, July 24, 2012 4:14 PM
To: pianotech at ptg.org
Subject: Re: [pianotech] Humidity

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