Terry,
Obviously you haven't had the good fortune to meet the folks from Dampp
Chaser. This company is one of the few who actually does Research and
Development. The people there are exceptional about assisting technicians.
They freely give advice, just as you saw today when they corrected me. But,
if you noticed, the method Roger used to correct me was a positive,
informative one. That is CLASS, and class is what Dampp-Chase has in
abundance.
Do they work hard to sell their product? Of course they do. How else to make
sure their company succeeds? Are their marketing techniques "hype." Nope,
not in my opinion.
Next time you can, do talk to these people. I think you will end up
respecting them as much as I do, and I don't think I'm the only one who has
a similar opinion.
My 2 cents.
Gina
----- Original Message -----
From: Farrell <mfarrel2@tampabay.rr.com>
To: <pianotech@ptg.org>
Sent: Wednesday, October 18, 2000 4:58 PM
Subject: Re: Different question about heater bars
"This humidity thing is always fun... and dont worry... even if I am blowing
air out of my better end,,, I still enjoy the conversation.. grin."
Me also!........But. Look at Dampp-Chaser marketing propaganda. All their
graphs about soundboards. Now I don't really think that they truely
represent the results of any particular experiment, but rather trends they
are trying to exemplify (although I do believe they should state that some
of the data in their brochure might be a bit idealized). Anyhow, as the RH
decreases in air in a piano, the soundboard Moisture Content also declines.
Moisture content is water in wood. Lower moisture content means less water
in wood. That means the water left the wood. It is no longer there. It does
not have anything to do with the amount of water the wood may be able to
hold (like RH). This is a central issue in wood technology - manipulating
the moisture content of wood.
It really, really is true. You can trust me! I is edgeekated. I got me a
deegree in Forestry (two lives ago)! So there! Top that! ;-)
Terry Farrell
Piano Tuning & Service
Tampa, Florida
mfarrel2@tampabay.rr.com
----- Original Message -----
From: Richard Brekne
To: pianotech@ptg.org
Sent: Wednesday, October 18, 2000 6:21 PM
Subject: Re: Different question about heater bars
Farrell wrote:
Gee whizz Richard. You of course know that it pains me to an
unimaginable
extent to suggest that my thoughts might be more valid and someone else
may
be, er, a, less than correct, BUT.....
You isolate the system far too much, and over simplify the situation as
such... grin... Number one.. you cannot discount the back side of the
piano.. or the exterior of the piano otherwise... Equilibrium will always
take the easiest path. And the easiest path is air ... from wherever it
leaks in...
That being said..... you will have to some degree the affects as you
describe them below... But on the other hand, you will also have the affects
as I describe them. Raising the temperature does indeed also lower RH in the
interior of the wood... whats good for the goose is usually (and in this
case as well, good for the gander.
Your Kiln example is a much more isolated system to begin with. And if it
was completely and totally isolated... where on earth do you think these
water molecules would migrate to ??? You put a panel into an oven that is
already dry inside... thats how it draws out water.. this isnt exactly the
same process as damp chaser creates.. tho admitedly some of the same
functions are at work.
I think you would aggree that takeing a panel and puting it into a kiln
which has the same moisture content in the air as the panel does in the
wood, sealing the kiln and turning it on wouldnt have exactly the same
effect.. now would it.
This humidity thing is always fun... and dont worry... even if I am
blowing air out of my better end,,, I still enjoy the conversation.. grin.
Lets say the RH of air in vertical piano interior is 70%, temperature is
70
degrees F and soundboard moisture content is 10%. Equilibrium conditions
exist (water molecules are evaporating from the soundboard surface at
the
same rate that water molecules from the air are imgrating into the
soundboard surface). Turn on heat inside piano. Raise temperature to,
say,
90 degrees F. The RH in piano interior immediately drops to perhaps 50%.
Immediately, the air inside the piano is capable of holding much more
water
vapor than previously. Water molecules will then migrate from the
soundboard
surface from within the wood and evaporate into the air inside the piano
at
a rate exceedingthe migration of water molecules migrating from the air
into
the soundboard wood. Hence there will be an net decline in the number of
water molecules in the soundboard (and a net increase in the amount of
water
molecules in the air within the piano - untill it leaks out and mixes
with
room air). That is what is meant by soundboard moisture content. That is
the
absolute amount of water "trapped" within the wood. It is not a mere
artifact of heating the wood and the air wihin the wood pores having a
lower
RH. A net volume of water will continue to escape from the soundboard
until
a new equilibrium is established between the RH of the piano interior
and
the water content of the soundboard. (We are or course neglecting the
fact
that the soundboard is also exposed to the outside air on the backside,
but
this does not change the course nor end point of this discussion.)
This is why when one dries a soundboard before installing into a piano
or
before shimming, the soundboard shrinks - because the board has an lower
absolute volume of water within it. You can prove this to yourself by
weighing a piece of wood before and after heating for a long time. It is
why
a freshly cut log is real heavy, but one of the same size and species
that
has dried for a year is much lighter - because water has been "drawn
out"
from the wood!
I think. I'm having fun watching language at work. I truely hope you are
also. :-)
Terry Farrell
Piano Tuning & Service
Tampa, Florida
mfarrel2@tampabay.rr.com
----- Original Message -----
From: "Richard Brekne" <Richard.Brekne@grieg.uib.no>
To: <pianotech@ptg.org>
Sent: Wednesday, October 18, 2000 2:33 PM
Subject: Re: Different question about heater bars
>
>
> Farrell wrote:
>
> > > Moisture is not exactly "drawn out" of
> > > the piano... rather the relative humidity is reduced.
> >
> > No and yes. Assuming that the air inside the piano is at some
elevated
> > reletive humidity and the soundboard is in equalibrium with those
> > environmental conditions. Now turn on the Dampp-Chaser heat rod.The
relative
> > humididy in the interior of the piano is indeed reduced. That sets
up a
> > non-equilibrium condition between the reletive humidity in the piano
> > interior and the moisture content of the soundboard wood. Because
the
air
> > has less reletive humidity and can now hold more humidity, there
will be
a
> > net movement of water from the soundboard to the air. So, it is
reasonable
> > to say that "moisture is drawn out of the piano and into the air.
>
> Grin... How fun it is to watch language at work. I'll buy your
interpretation of
> the words "moisture is drawn out of the piano and into the air" in
this
> connection. Its actually what I was saying. Still, from the other
standpoint..
> absolute humidity remains the same within the wood as it does within
the
air..
> expanding the air surrounding air, and thereby decreasing Relative
humidity does
> indeed create the non-equilibrium you describe, but as to whether or
not
one
> describes the equalizing of this in terms of "drawing out humidity" or
rather
> that the soundboards air content also expands, retaining the same
volume
of
> absolute humidity is ...grin.. up for discussion... I would choose the
> latter.... for ..... clarity...hehe..
>
> Keith.... sorry to be so picky...:)
>
> >
> >
> > Terry Farrell
> > Piano Tuning & Service
> > Tampa, Florida
> > mfarrel2@tampabay.rr.com
>
> --
> Richard Brekne
> RPT, N.P.T.F.
> Bergen, Norway
>
>
>
--
Richard Brekne
RPT, N.P.T.F.
Bergen, Norway
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