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Humidity, the great
unseen factor in your pianos
behavior.
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Climate Control and
Stabilizing Pitch
by Lou Tasciotti
Lou Tasciotti is Technical
Editor for The Piano
Quarterly,
Piano Technician at The
Crane School of Music,
Potsdam College of the State
University of New York, and
a
Registered Craftsman in
the Piano Technician’s
Guild.
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A piano
tuning, taken as a noun, is
an intangible, subjective
and often too temporal state
of being. All things being
equal, it is the temporal
aspect of a tuning that is
often used to praise or
condemn the quality of a
piano technician's work. And
understandably so what good
is the best tuning if it
doesn't last? There are
however, two factors to
consider here that will
determine the longevity of a
piano tuning. The first,
obviously, is the skill of
the technician. The second,
is the environment that the
piano resides in.
How does one differentiate
between these two factors to
find out why a piano tuning
may be short-lived? A simple
test will give you the
answer. Immediately after
the piano technician has
left, sit down and quietly
listen to the tuning,
especially the purity of the
unisons. This is the time to
judge the accuracy of the
tuning as well as to get
familiar with it. Assuming
that you are satisfied with
the way the tuning sounds,
proceed to play the piano
very vigorously. After
giving the piano a good
workout for about half an
hour, listen to the tuning
again. If the tuning
survived, then it was a good
one. From this point on the
tuner has no control over
what happens. Whether or not
the tuning sounds good the
next day, the next week or
three months later, is up to
you. Providing the right
environment for your piano
is what will now determine
the longevity of the tuning.
The right environment for a
piano is one that is stable
in temperature, and even
more important, in humidity.
A stable environment will
not only extend the life of
a tuning, but will also
extend the life of the piano
and reduce future
maintenance costs.
The first step in providing
a stable environment for
your piano is to select the
right location. Placing your
piano next to a radiator,
heating vent or wood stove
results in a most damaging
environment.
Keeping your piano at least
five feet away from any heat
source is a safe rule of
thumb, and be sure that no
hot air vents are blowing in
its direction. Drafty doors
and windows should also be
avoided, and even keeping
your piano away from air
return vents in-forced air
heating systems is a good
idea. Direct sunlight will
also have a very deleterious
effect on your piano. In old
houses with little or no
insulation, you should also
avoid placing your piano
against an outside wall.
Following these fundamental
guidelines will keep you
from making any serious
mistakes when providing for
your piano, but this is just
the beginning.
Pianos are wooden
instruments and wood is
extremely sensitive to
humidity changes: it shrinks
when the air is dry and
expands when the air is
humid. Changes in
atmospheric humidity are the
real culprits for putting a
well-tuned piano out of
tune.
One of the most
humidity-sensitive parts of
a piano is its soundboard.
Piano soundboards are truly
remarkable in their
construction. Only 3/8 of an
inch thick at its center, a
soundboard can be upwards of
six plus feet long by four
plus feet wide. Furthermore,
a soundboard is curved.
Supported on its underside
(in a grand) by a series of
one inch wide ribs, this
thin sheet of soft wood is
strong enough to withstand
several hundred pounds of
string pressure pushing down
on it.
Like all stringed
instruments, the soundboard
of a piano is straddled by a
bridge. The strings pass
over the bridge which
transmits vibration to the
soundboard. An increase in
humidity causes the piano's
soundboard to expand. Since
the sound board is curved
(upward in a grand), it
rises up, pushing the bridge
and the strings up as well.
This increases the tension
on the strings and causes
their pitches to go sharp.
Likewise, a decrease in
humidity will shrink the
soundboard and the pitches
will go flat.
Whether a piano has been
played or not, a large
change in humidity will have
a drastic effect on the
tuning. Some of the concert
grand’s that I care for
receive up to twelve hours
of use each day including
perhaps four recitals on any
given day. During periods of
relatively constant humidity
I have seen these heavily
played instruments remain
almost in perfect tune over
the course of several weeks,
requiring merely touching up
an occasional slightly stray
unison in that time.
However, during periods of
unstable humidity I have had
to completely retune these
same instruments almost
daily. Obviously,
controlling humidity is the
key to having a good tuning
remain stable.
There is a relationship
between humidity and
temperature. Warm air is
able to hold more moisture
than cold air. At any given
temperature there is a
maximum amount of moisture
that the air can hold. This
maximum amount is referred
to as 100% relative
humidity. If you heat the
air without adding any
additional moisture, you
will lower the percentage of
the relative humidity
because the warmed air can
hold more moisture. This is
what happens when you heat
the air in your home. The
relative humidity goes down
as the temperature goes up.
Porous objects such as your
piano contain moisture.
Their moisture content will
seek to reach an equilibrium
with the air. As the
relative humidity of the air
goes down, the air will act
like a sponge-and draw
moisture out of any porous
object. Conversely, when the
relative humidity goes up,
porous objects will draw
moisture from the air. To
keep your piano from
experiencing radical changes
in humidity, it is necessary
to add moisture to cold air
as you heat it and remove
moisture from warm air that
has too much moisture in it.
What is the ideal relative
humidity for a piano? The
ideal humidity is far less
important than the
consistency of the humidity
level. Although 30 to 10%
relative humidity is a
considerably dry
environment, a piano that
has been acclimated to this
environment and kept between
30 to 40% will remain quite
stable. Whereas, although 45
% relative humidity is
considered fairly optimal, a
piano in an environment that
fluctuates from 35 to 55% is
going to require a lot more
tuning as well as other
maintenance.
Avoid extremes. A relative
humidity of 30% or less is
an invitation to trouble. In
this dry environment you run
the risk of having wood
parts of the piano crack and
glue joints fail. At 60%
relative humidity or higher,
piano strings and tuning
pins may start to rust.
I suggest you buy yourself a
hygrometer to measure the
relative humidity and keep
it close to the piano.
Hygrometers, usually coupled
with thermometers, are
fairly inexpensive - ranging
from the $6.00 hardware
store variety to the $30.00
decorative style found in
home furnishing stores. For
the sake of accuracy, make
sure that you keep it away
from heating vents, drafts,
direct sunlight, and outside
walls.
There are essentially three
ways to control the humidity
changes that your piano may
experience. If you have a
forced air system, you can
have a humidifier built
directly into your central
heating/air conditioning
system. Otherwise, use a
portable humidifier in the
dry season and a portable
dehumidifier and/or air
conditioner in the humid
seasons. A third approach is
to have a miniature
climate-control system
installed by a piano
technician directly onto
your piano.
It would be ideal to
stabilize the total
environment that the piano
is in, but this isn't always
practical or economical. In
areas with extremely cold
winters, unless you have a
very tight house with
excellent thermally
insulated windows, trying to
keep the humidity level up
can be a bit of a problem.
The extra moisture will
condense when it comes in
contact with cold surfaces
like non-thermal windows or
un-insulated walls. This
type of condensation will
cause wood surfaces to rot.
Portable humidifiers are
also rather annoying to use.
They must be refilled. With
water very often, cleaned
occasionally, and can be
rather noisy. The new breeds
of ultrasonic humidifiers
are almost silent, but need
to be refilled more often
and don't have the same
output as the older floor
model type. Another problem
with portable humidifies is
that if you go away on
vacation they may not get
filled and thus the room
will get quite dry.
A climate control system
installed directly onto your
piano can be very effective.
This type of system consists
of a low-wattage heating
element (dehumidifier) and a
water reservoir with an
evaporator (humidifier) that
mounts on the underside of a
grand piano or inside the
bottom of an upright. The
system is controlled by a
humidistat that turns on the
humidifier or dehumidifier
as needed. There's even an
indicator light to tell you
when to refill the
reservoir, which is usually
never more than once a week.
The one drawback of this
type of system is that it is
localized and its beneficial
effects don't extend equally
to the entire piano. While I
recommend these systems as
being economical, effective,
and maintenance-free, I
suggest that they are
supplemented with a room
humidifier in extremely dry
environments.
Aside from changes in
humidity, there are other
reasons why a well-tuned
piano in good condition can
go out of tune. When a
string breaks and is
replaced, the new string
will go out of tune within a
matter of hours. New strings
will stretch for weeks or
even months. New pianos or
newly restrung pianos
require far more tuning in
their first year than they
will later on. But one of
the most common causes for a
well tuned piano to be
unstable, assuming that both
the tuner and the piano are
good, is that the pitch has
not been stabilized.
Stabilizing the piano's
pitch means not making any
radical changes in the
overall pitch of the
instrument. Many European
orchestras tune to A-442 or
higher, as opposed to U.S.
standard pitch A-440.
Pulling a piano up to a
higher pitch is going to
leave the tuning unstable.
This kind of major change in
the pitch of a piano demands
that the piano be tuned more
than once to stabilize the
pitch.
As solid as pianos may
appear, they are in many
ways quite flexible. Not
only do they expand and
contract with changes in
humidity, but they also
react to changes in tension.
The string tension in a
piano is enormous, with a
combined tension of upwards
of 35,000 pounds. This
tension translates into
roughly 1,000 pounds of
pressure bearing down on a
typical soundboard and its
bridges. Any change in
string tension is multiplied
by the approximately' 240
strings. As strong as the
soundboard has to be, it
must also be flexible so
that it can vibrate freely.
Therefore, even a relatively
small change in string
tension is going to have an
effect on the soundboard.
Since the pitch of the piano
must be kept relatively
constant, any substantial
changes will cause the
soundboard and bridges to
begin flexing. Pulling up
the pitch in one octave will
cause a previously tuned
octave to drop in pitch, and
vice versa. Even if a
technician goes over the
tuning several times, the
piano will continue to be
unstable for days
afterwards.
The only way to achieve
timing stability when you
have to substantially change
pitch is through a series of
tunings. The number of
tunings needed for the piano
to stabilize depends on how
much the pitch has to be
altered. The first and
second tunings in a major
pitch changing process do
not really resemble tunings.
After the radical pitch
change a piano may not
necessarily sound any better
because it is still out of
tune, but at least the
overall pitch of the
instrument is in the right
ball park. Technicians
usually refer to these
preliminary tunings by other
names, such as pitch
raising, pitch lowering, or
shop tunings.
How far out of tune does a
piano have to be to require
more than one tuning? It is
generally accepted that a
pitch change of eight cents
or more will exhibit
noticeable instability. For
those readers not familiar
with the term cents, one
hundred cents equal one
chromatic half step. So,
from the point of tuning
stability, if a piano's
pitch is off by a quarter
tone (50 cents), that is
considered extreme.
To give the reader an idea
of how far out of tune
pianos can get from one
season to the next, let me
provide the following
example. I set a piano aside
to remain un-tuned and un
played for a period of one
year. The pitch of one note
(A = 440 Hz) was measured
each day, along with the
relative humidity of the
room containing the piano.
The relative humidity
recorded was typical of the
extreme range that we find
in New England. That is,
some relatively humid
springs and summers and very
dry winters. The indoor
.relative humidity recorded
in the room where the piano
was located varied from 65%
in July to 19% in February.
During that time, the
maximum pitch change was 29
cents. If we divide this
pitch change, 29 cents, by
the maximum amount of change
allowable for a stable
tuning, 8 cents, as
mentioned above, we find
that this piano would have
had to be tuned at least
three times between July and
February. Add these two
tunings to the other three
and we find that this piano
needed to be tuned five
times, if we want each
tuning to be stable. That is
a lot of tuning.
This kind of pitch
instability is an
unnecessary problem. Using
an effective form of climate
control can reduce the
seasonal pitch changes of
the piano to a negligible
amount. Your tunings will
last a long time, and when
you finally do need the
instrument attended to, it
will be a bit of a luxury
instead of a desperately
urgent situation. |
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