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" <[email protected]>
To: <[email protected]>
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 here -
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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