Hello Chris:
You might (if you haven't already) get David's instructional
courses in
either Renaissance or Baroque Lute building.
there is an excellent section there on EXACTLY how to deal with
humidity.
I have repaired now and restored a number of lutes in which it
was clear
to me that the humidity in which the cross braces were installed
was TOO
high (around 48 to 50% ) where the bridge was installed at a
different
humidity a good 5% higher even still thus creating instabilities and
compromises in sound relative to what the instruments were actually
capable of .
In my own shop I built a proper Go Bar chamber (modeled along the
lines
that David Suggests) where in addition I used 2 layers of Foam
Core all
around the sides thus turning it into something like a foam coffee
cup.INside the chamber as David suggests, I installed a light
socket where
I use several different lamps to lower humidity - higher wattage
the lower
the humidity for a given amount of time in heating - this
relative to the
humidity in the shop, and where I also have a room humidifier if
that is
necessary as well. There is also a hygrometer inside the chamber.
where I disagree with one of the posts ( If I read it correctly )
is that
I believe that generally humidity goes DOWN with cold and UP with
warmer
air - THis is why you might note floorboards and furniture
creaking in
extreme cold and is why most all total house humidifiers as used
with
central air systems use the warm air of the heater to first
vaporize the
water as injected into the plenum and then use the ducting to
move the
humid warm air into the house. HOWEVER if you know SoCal, you
know that
we have Santa Ana's which are winds of warm to hot air coming in
from the
desert, and are composed of EXTREMELY dry air . So general truths
about
humidity vs temperature need to be modified according to the
geographical
conditions in which you live
In my experience with the Spanish Masters in Spain ( I knew Arcangel
Fernandez de La Mata, Marcelino Lopez Nieto , Manolo Contreras
well, and
visited often the shops of Hernandez & Aguado, Ramirez and Reyes in
Cordoba) they only did their glue ups on tops during the later
part of the
summer when they knew the humidity to be around 5 or so percent
LOWER than
the typical humidity in which the instruments were to live. If
you are in
a higher humidity climate such as London , you might want to
brace and
bridge your top at 44 percent or so. Here in So California I
brace at 32
to 35 Percent. New Mexico- at the lower end of the scale. David
goes into
excellent detail here.
WHY?
there are 2 reasons in my opinion.
Firstly there are two ways cracks occur with tops. ONE is that
simply the
top is braced and bridged at a noticeably higher humidity than
its current
environment . This creates extreme stresses in the top as it
wants to
shrink laterally like a squeezed accordion as a function of
carrying less
moisture but the braces won't let this happen and the bowl also
"freezes"
the top to its general dimension when it was glued up in an
environment
which was higher in humidity. All this is to essentially stretch
the top
like a drum head as the top itself wants to shrink.
In this scenario the top goes concave which will have the effect
also of
lowering the action a bit. At first (and only at first) the
instrument
will sound quick and with a nice amount of high frequency energy
- finally
to lose its warmth and bass depth. But when the stresses build
up to a
high enough level and overcome the capacity for the summer growth to
sustain cellular connectivity along the grain line, the top will
crack at
that point and relieve the stress that has been building up. The
second
way is that if the instrument is in a MUCH HIGHER humidity
environment
than that for which it was intended, the moisture will swell the
top and
the opposite effect will occur, that is that the top will want to
expand
but the braces but as before the bridge and bowl will prevent
this. Here
the top in being squeezed will actually crush itself along the
summer
growth grains ( being the softest) and belly upward raising the
action
and making the instrument sound dull . IN GENERAL the top will
not crack
here , but having been crushed in the process by X percent , the
top will
be MUCH MORE likely to crack during a period of lessor humidity.
So the answer is for at least the first reason ,to deal with the
problem
of catastrophic failure , that the top should be braced and
bridged at a
humidity a bit or so below the average humidity in which the
instrument is
expected to live.
Secondly , and this is related to sound (and a view which I
have sort of
inherited), you want the top to be RELAXED at all times -and
that this is
crucial for the instrument to develop a good pianissimo and sustain.
If there are any built in stresses , as soon as the sound
imparted to the
instrument top by the string drops in energy to the approximate
level of
energy as represented by the built in stress, the sound will not
be able
to uniquely vibrate the top as the stress' will now begin to
dominate and
prevent this . SO we want to make sure that the braces EACH ONE
are glued
onto the top with the top being within 1 or maximum 2 percent of
your
base humidity in the chamber. as well the bridge - here with the
bridge
David suggests one can be a little looser but not by much.
I also recommend that the top be allowed to sit in your go bar
box at the
correct humidity for at least 4 hours if not more like a day or
two so
that it really stabilizes there before gluing on braces.
I don't know about harps, and what the requirements are there-
beyond the
fact that you have to be REALLY GOOD to build a harp (daunting
things
harps ....) , but I do suggest the above ideas. Remember a lute
top is
wide and REALLY thin.. and this is where the issues arise.
best
Richard Lees
----- Original Message ----- From: "Chris Newman"
<chrisdnew...@btinternet.com>
To: <lute-buil...@cs.dartmouth.edu>
Sent: Tuesday, February 10, 2009 1:47 PM
Subject: [LUTE-BUILDER] moving soundboard from workshop to house
Dear All
As a new lute-builder I am very much appreciating the
discussions ere -
but have a newbie-type question
I am renting bench-space in a quite large workshop, it's not
warm but has
background heat to keep the temperature from dropping to
unmanageable
levels (we're having a cold (for the UK) winter here).
but I live in a centrally heated house, where my wife loves to
keep us
very warm and cosy - above 25C.
I would, however, like to be able to bring my soundboard into
the warm
and carve the rose on the kitchen table
but I'm worried that the changes in temperature (and humidity? -
I've
just ordered a simple hygrometer to check this) might be too
much for the
soundboard?
any advice very gratefully received
regards
Chris
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