Temperature Change affecting pitch

[Farrell]

The point was that ANY properly operating AC unit will physically remove
water vapor from the air. They are designed to do this so that they do not
have to cool the air excessively to make the air feel cool. In my shop I
have a dehumidifier wired to a DC humidistat. It keeps the RH in the shop at
about 60% RH (Hmmm, why not 42% like the brochure says?). When I turn the AC
unit on, the temperature starts dropping and the humidity usually drops a
good 5 to 10% pretty quickly.

Terry Farrell
Piano Tuning & Service
Tampa, Florida
mfarrel2@tampabay.rr.com

----- Original Message -----
From: "Richard Brekne" <richardb@c2i.net>
To: <pianotech@ptg.org>
Sent: Thursday, March 30, 2000 2:14 AM
Subject: Re: Temperature Change affecting pitch


> Hmmm... looks like we need an in depth understanding of why and how
relative
> humidity changes.
>
> You have to understand that there is something called relative humidity
and
> something called absolute humidity. AH is exactly how much humidity there
is in
> a given volume of air. RH tells us what percentage of maximum AH there is
in the
> air at any given time. The reason for RH is that the maximum amount of AH
> changes with the air temp. Hot air can "hold" more humidity then cold
air...
> ok...
>
> now think about this example. Nice partly sunny day outside.. with outside
> temperature of 90 % and an outside RH of 75 %. (Early summer / late spring
in
> Iowa ??? grin) You are sitting in your house and get to feeling to warm so
you
> turn on the airconditioner which takes the outside air as it is... humdity
and
> all and cools it down while pumping it around inside your house. The air
gets
> compressed with cooling yet there is still the same amount of humdity per
volume
> unit (AH) stuck in the air. This means that the air now has a higher RH
factor
> as that same AH amount now relates to a lower temperature and thus
represents a
> higher percentage of the maximum amount of humidity the air at this lower
> temperature can hold. You cool this outside air down enough and its going
to
> start raining somewhere in your house...(grin... overdriven point dont you
> know).
>
> The same thing happens in reverse in the winter. Warm air expands, and
unless
> you add humidity to that air... then the AH stays the same but the air can
hold
> more.. so RH goes down. Remember. RH only tells us what percentage of the
> maximum amount of humidity the air can hold at any given temperature. It
does
> not directly tell us how much humidity there is in the air itself.
>
> Think this through... it can be difficult to sort out at first... but it
makes
> sense enough after a while. In your example RH would go up if and only if
> nothing is done to remove some of the humidity from the air after / during
the
> cooling process. Some airconditioners do this well, some dont, some too
well. It
> all depends on how its installed, and what kind a unit it is, and what the
> conditions its operating in are like.
>
> Really tho... thats why we have these handy gadgets like RH readers. All
you
> really need to do is place that by the piano and see what it reads. And if
you
> are interested in seeing the affect of the inner environment (in a rough
sense)
> on that RH reading you get... go outside for a few minutes and check what
the
> outside RH is. If its different... then something inside the house is
either
> drying out / or adding damp to the air.
>
> Farrell wrote:
>
> > Now why would turning on the AC make a piano go sharp? The cooler temp.
> > would make the plate and case contract (albeit very slightly), thus
lowering
> > pitch, and the lower humidity (because any properly operating AC unit
will
> > remove water from the air, thus lowering relative humidity) would tend
to
> > make the soundboard contract, again lowering the pitch. Why in the world
> > would it go sharp?
> >
> > Terry Farrell
> > Piano Tuning & Service
> > Tampa, Florida
> > mfarrel2@tampabay.rr.com
> >
> > ----- Original Message -----
> > From: "pryan2" <pryan2@the-beach.net>
> > To: <pianotech@ptg.org>
> > Sent: Tuesday, March 28, 2000 11:02 PM
> > Subject: Re: Temperature Change affecting pitch
> >
> > > I learned the hard way that temperature has a immediate effect on
pitch.
> > > When I go into one of the showrooms to tune a piano, I click on the
air
> > > conditioning (I'm in South Florida), proceed to strip mute a piano and
> > begin
> > > tuning middle strings with the SAT.  After getting half way through
the
> > > piano, I go back to where I started and re-check my work. All the red
> > lights
> > > are spinning sharp now. What do I do now? Start over or let them go?
> > What
> > > I do now is turn the AC on in advance and let the showroom and pianos
to
> > > cool down before starting.
> > >
> > > Phil Ryan
> > > Miami Beach
> > > -----------------------------------------------------
> > >
> > > ----- Original Message -----
> > > From: "Larry J Messerly" <prescottpiano@juno.com>
> > > To: <pianotech@ptg.org>
> > > Sent: Sunday, March 26, 2000 7:15 PM
> > > Subject: Temperature Change affecting pitch
> > >
> > >
> > > > Just for my own information, when I came into my store this morning
I
> > > > took pitch readings on two grands at 61degrees F. then turned on the
> > > > heating system and raised the temperature to 68 degrees.
> > > >
> > > > The 6' Kranich and Bach dropped pitch 3.2 cents initially and then
when
> > > > (I presume) the plate temperature rose ended up 1.6 cents flat of
where
> > > > it had begun the morning.
> > > >
> > > > The 5'3" George Steck initially dropped 0.4 cents then continued to
fall
> > > > to 1.2 cents from where it had been.
> > > >
> > > > They have not changed any more over the last hour.
> > > >
> > > > No real problem or question here, just thought it was interesting.
> > > >
> > > > Larry Messerly, RPT
> > > > Phoenix/Prescott
> > > >
> > >
> > >
>
> --
> Richard Brekne
> Associate PTG, N.P.T.F.
> Bergen, Norway
>
>
>