"Tony Caught" <caute@accessnt.com.au>

[Woodrow, John (Parramatta)]

Tony,
Thanks for the feedback.  I would like to expand on some of the points you
raise and would appreciate your comments.

How does one define the 'tropics'.  For six months of the year, coastal
Sydney has humidity levels of 70+% and temperatures of mid 20's to mid 30
degrees Celsius.  This is not much different to the coastal Queensland towns
for all but maybe the 3 months of summer when the humidity goes a bit higher
and its slightly hotter for longer during the day.  

My logic for considering the 'wet' DC is simple. If the DC is trying to
create an environment under the soundboard of 42%, and the external
environment never gets below 55%, then the DC will be permanently on and
flat out trying to dry the board down to a level that this piano has not
experienced since it left the Kawai factory 15 years ago.  Isn't this asking
for the same problems as transferring an old piano from one environment to a
greatly different one.  This is exactly the issue that you stated when you
said that "the issue of a tropical or wet humidistat of 55% RH was developed
to ensure that the heater was not on all the time and that the piano
moisture content was not reduced too much more than the lowest level of
moisture content.

As the lowest RH recorded over the past several months was around 55% for a
perior of only a couple of days, a 42% humidistat must be on all the time,
and the piano moisture content will be reduced too much lower than the
lowest level of moisture content.  Surely the 55% RH humidistat is closer to
the mark if I go ahead given the feedback from guys like Roger Jolly who
said 'let it be'.

Appreciate your comments.

Regards,
John

Date: Tue, 1 Feb 2000 22:50:18 +0930
From: "Tony Caught" <caute@accessnt.com.au>
Subject: Re: Dampp Chaser or not, that is that question!

John

If you were in the tropics, yes I would go for the 55% humidity bar, but you
are not.
What you have to remember is that their are two factors that control the
moisture content of the timber in the soundboard (piano), humidity and
temperature.

I have a copy of the moisture content of various timbers as registered with
the CSIRO that cover most of Australia.

You will find that in Newcastle the moisture content for Radiata Pine is
very stable, varying 1 degree only from 15% to 16% with the average of 16%.
Sydney, for the same timber in the same thickness (1/4") varies between 13%
and 16% with the average of 14%.
Melbourne goes from 12% to 17% with an average of 14%.

Parramatta being further inland (not much but further) than Sydney, a little
less humid, thus you could expect the moisture content to be lower.

Pianos in general are made with a moisture content in the soundboard of 8%.
This 8% is expected to increase to say 12 or 13% to increase crown etc. but
that is another story. My point is that with your lower average
temperatures, you require a lower humidity level in the soundboard.  Go for
the standard 42% humidity Dampp-chaser system, it will give you a better
sound.

Here in Darwin, today the temp was 33 Celsius and 90% humidity.  Now if I
was to install a D-C with 50 watts of heat it would bring the RH in the
piano down to 40% (rule of thumb 'for every watt of heat you remove 1% of
humidity') but that would mean that the heat would remain on constantly and
that in turn may cause considerable damage to the piano.
However the moisture content of the same timber in the tropics for Cape York
are 17% to 21% with a mean of 19%, thus a tropical or wet humidistat of 55%
H was developed to ensure that the heater was not on all the time and that
the piano moisture content was not reduced too much more than the lowest
level of moisture content.

Stick with the standard 42% is ideal around that area.

Tony Caught IC PTG Australia
caute@accessnt.com.au

- ----- Original Message -----
From: Woodrow, John (Parramatta) <John.Woodrow@pil.com.au>
To: 'Pianotech List' <pianotech@ptg.org>
Sent: Tuesday, 1 February 2000 10:10
Subject: Dampp Chaser or not, that is that question!


> List,
> Piano is a Kawai GS-30 grand that I am guessing is about 14 years old.
The
> piano is an ex-institution piano currently being restored.  It has lived
all
> its life in a mild coastal environment (60-90 F) where one can be pretty
> certain the relative humidity of its environment was greater than 50%.
The
> soundboard has a few noticeable pressure ridges but nothing extreme. Board
> has minimal crown (although much the same as every other GS-30/40
measured),
> pins are TIGHT!  The to be restrung strings are rusty.
>
> The piano is now located in a room that the humidity swings from 60% to
80%.
> On occasions it dips briefly to 50% on very 'dry' days.
>
> So my question to the list is do I:
> (a) install a DC de-humidifier (tropical version which is set at 55% or so
I
> believe), or
> (b) because the piano has lived in a high humidity environment all its
life
> and settled into that groove just leave it alone.
>
> I am concerned that the pressure ridges may open up if the DC is
constantly
> trying to pull the humidity down from the 70% to 55%.
>
> Appreciate the wisdom of the list on this one.
>
> Regards,
> John Woodrow
> Sydney, Australia ICPTG.