An Article by Ken Eschete, RPT
As technicians, we are expected to be experts on every aspect of the piano, including
the soundboard. It’s good to remember that the piano is classified as a percussion
instrument because the sound is created when it is struck with a mallet. Just like a
timpani drum, the sound is affected by the drum itself (the piano soundboard), and by
what sort of mallet is being used to strike the drum (the piano action and hammers). If
there are problems that are evident with the soundboard, spending time on regulating
and voicing will meet with very limited results.
In museum conservation, we use the term ‘Inherent Vice” to describe deterioration of an
object that is being caused by the method in which it was created. Pianos made during
what we call the “golden era” have a common inherent vice. The manufacturing of the
soundboards required a warm environment for the use of hide glue. The wood had to
be warmed in order to keep the glue from setting too soon. Warming the soundboard
panel has the effect of lowering the moisture content to as low as 2% equilibrium
moisture content (EMC). These conditions were maintained while the ribs were glued
onto the underside of the soundboard, and when the soundboard was glued into the
rim.
When normal temperature and humidity levels returned, the wood cells in the
soundboard panel take on moisture from the air and the soundboard tries to expand.
Because it is glued down on its edges, and because the ribs restrain any expansion on
the underside of the soundboard, it takes on a crowned shape. This is known as
“compression crowning”.
There is a long-term effect from all this built-in compression. Over time, the wood cell
walls begin to break down, weakening the wood and making it subject to forming
cracks. The other contributing factor is the shrinkage that occurs with age. Together,
these factors cause the crown to disappear; and as a result, there is a loss down-
bearing. The result is a dull, unresponsive sound.
Another prominent factor that causes the deterioration of the soundboard is radical
fluctuations in the moisture content of the wood. A good deal of scientific examination
in museum conservation labs has provided evidence that when the humidity in the air
swings between high and low levels, it is more destructive than if humidity levels are
steady, even if they are outside of the ideal range of between 40 and 60%RH. These
swings can be naturally occurring because of seasonal changes, but they are also
artificially created when humidifiers are allowed to go empty, and then are replenished.
This problem still occurs, even when humidifying systems are employed. Some of the newer systems provide better monitoring of conditions. When problems are occurring,
they can be communicated via an app on a cell phone.
Rebuilding Option One:
Many rebuilders believe that the crown can be restored by re-attaching loose ribs and
shimming the cracks with spruce. If this work is carried out after warming the
soundboard with heat lamps, a crown shape may reappear. Unfortunately, this crown
generally goes away as soon as string tension is applied. (I myself was under the
impression that this worked until someone pointed out to me that I should test for crown
after the string tension was back on the piano. It was a revelation.)
Going along with shimming the soundboard, restores often lower the height of the plate
by cutting away the plate support dowels. This is a method that works inconsistently,
since any plate height adjustment that increases down bearing for the middle of the
range, is often detrimental to the bass and treble ends.
Another problem is that many of these pianos have already been through a rebuilding
process, sometimes more than once. Unless humidity has been strictly controlled,
cracks soon reappear in the same places or right next to the old cracks. This is very
disheartening and very difficult to repair. I sometimes think of a parallel in dentistry,
where the first step is to crown a tooth, which often is followed by a root canal, which
sometimes leads to tooth extraction.
There is a way to restore the original soundboard so that it has crown, and this is done
by some restorers of historic pianos. The original soundboard must be removed intact
and then placed it in a shallow pool of water. Over time, all of the glue joints come apart.
Once the original components are dried and straightened, they can be glued back
together again, with the addition of some new wood along the edge to make up for the
age shrinkage. This is not practical for the modern piano, but it remains a possibility.
Option two:
For those pianos that have already been to a restoration shop, replacing the
soundboard and bridge caps is a very good option. There is nothing magical about the
old soundboard wood. Suppliers can provide replacement soundboards of equal quality.
One option is known as a “board in a box”. This is when the old soundboard is crated
and sent for duplication. When crate is then returned, it contains a duplicate
soundboard, along with the original soundboard. Additionally, the rebuilder can request
that the bridge caps be replaced. The rebuilder will receive instruction on how to install
the bridge in the correct place and how to glue the soundboard into the rim. (It is still
necessary for the rebuilder to learn to learn how to set down-bearing, drill bridge pin
holes, and notch the bridge. Our online course can provide this instruction.)
Going a step further, rebuilders can make their own soundboard press and avoid the
“board in a box option”. This allows the rebuilder to control more aspects of the
rebuilding, and increases the profit. This also means that the rebuilder is able to make
effective improvements to overcome the “inherent vice” of the original design. The
original flat ribs can be replaced with ribs that have a radius cut into the surface. A
method of recalculating the “rib scale”, has recently become available in the form of an
excel spreadsheet. ( now available on this website).
How to learn about soundboard replacement?
Since 2015, technicians around the world have successfully learned the craft of
soundboard making by taking an online course published by Ken Eschete and Gini
Gorlinski. This is a unique collaboration between an experienced craftsman and the
professional designer who specializes in writing online courses. It is a hybrid of video
instruction and hands-on assignments that are reviewed by an instructor, Ken Eschete.
The first step in the course is to construct a practice jig. Plans for the jig are included as
a downloadable full-size drawing, which students have printed at any print shop with an
oversize printer. The jig has all the elements of a grand piano rim, including the inner
rim with notches for ribs. Every step of the process can be carried out using this jig for
practice. There are 10 modules, each with an assignment for the student to carry out,
photograph, and post on the platform for review. When the work is accomplished
successfully, the next module unlocks so that the student can continue. In this manner,
the instructor is able to closely follow how the students are progressing. It also ensures
that no student can’t rush the process without being carefully reviewed. This is how we
are able to certify students who have completed the course. ( The soundboard course
has also been translated into the Spanish language and is available now.)
The professional piano technicians network, Pro PTN, is republishing the edited course
on soundboard making and bridge capping using a new platform. Projected availability
in 2026. Watch this space for further release details and pricing.