[pianotech] Harpsichord soundboard ribbing

[Rex Roseman]

Frank

 

I notice that no one has responded to this so I will dive in with some
thoughts.

 

Evan J. Kern in his book "Harpsichord Design and Construction" on page 31
says that the ribs on the bottom of the soundboard act as a cutoff bar to
limit the vibrating area and to support the soundboard. The bridge also is
part of the support system. This is why the soundboard assumes an "S" shape,
starting from the cutoff bar and rising before the bridge and dropping to
meet the bridge, then dropping again after the bridge and rising again to
the case. Part of the reason for this construct is that "modern"
harpsichords, for the most part, are copies of older instruments. (There was
a period of extreme experimentation during which one will find anything.)
The historic harpsichord maker was not a piano builder who started to make
harpsichords, but usually a stringed instrument or organ maker. The pattern
of construction of the earliest instruments follows that of a viol with the
entire outside of the instrument being a vibrating box. [Note I said
pattern, not exact duplication. This was more of a way of thinking and
approaching construction then duplication of construction exactly.] This is
why early harpsichords were "inner/outer" instruments; the instrument itself
(the inner) was very fragile and light, and it was stored in a case (the
outer) when not being used. Later, the case was incorporated as the sides
and bottom of the instrument. If you look at the molding and detail work in
later harpsichords, you will see the lines of demarcation that would have
been the separation of the two parts.

 

Kern also shows a way of bracing that resembles the ribs of a modern piano.
Frank Hubbard in "Three Centuries of Harpsichord Making" Plate II #4 shows a
similar design in an Italian harpsichord. With the exception of these two
sightings, the standard pattern was to run a cutoff bar across the bass and
brace the non vibrating area. Kern also states on the same page that the
bridge is a major part of the support for the soundboard. If one looks at
the Plates in Hubbard's book, it will be seen that a harpsichord with a 4'
stop will have a second bridge and hitchpin rail fastened to the soundboard
to add additional support.

 

As far as the problem of the strings hitting the soundboard, I have no
definitive answers. I have seen it and can give possible reasons. The first
one being that well built historical copies are built to withstand the pitch
at A=415. Most instruments scaled this way have a transposing keyboard so
that it can be played up a half step at A=440. My experience has been that
making sure the instrument is tuned so the lower transposition is A=415 and
the upper transposition shift is A=440 will go a long way in solving a lot
of basic problems. May seem obvious to some, but it was a real "Aha" moment
for me when that light bulb went on. One of the solutions may be to take
enough pressure off the soundboard to let it drop. Also, a historic copy
strung with modern strings could put to much pressure on the board and
exaggerate the curve.

 

Part of the soundboard hit the string problem may have to do with the
climate the instrument was built in and where it currently lives. At the
undergraduate school I attended, the harpsichord had to be kept in a special
room in the air conditioned science building with a dehumidifier going all
the time to keep it playable. I am not sure they ever did solve the problem.

 

Opening from the bottom may not be an option as the integrity of the case is
most likely dependent on a set of braces glued/screwed to the bottom and
sides. It may be better to unstring the instrument and come in from the top,
possibly treating the bulging as a soundboard repair and taking a sliver of
wood out to relieve the pressure. I have not done this and am not sure that
it would work, just trying to get the creative juices flowing on the list.

 

There are a couple people on the list that are much more experienced in this
then myself and I would be interested in their take on the situation.

 

Rex Roseman

 

-----Original Message-----
From: George F Emerson [mailto:pianoguru at cox.net] 
Sent: Tuesday, July 13, 2010 3:25 PM
To: pianotech at ptg.org
Subject: [pianotech] Harpsichord soundboard ribbing

 

Harpsichord tech's:

 

In my limited experience with harpsichord service, it has always seemed odd
that the ribbing patterns are so irregular and seem to avoid crossing under
the bridge.  This combined with the back pinning of the brdige seems to
cause the "crown" to distort in a rough S-shape.  In two cases, I have seem
such distortion that the vibrating strings, in some areas, buzz on the
surface of the soundboard.   What is the best way to repair this?  Is there
a logical reason to avoid having ribs corss under the bridge(s)?  I expect
that it needs to be opened from the bottom and some modification made to the
ribbing to provide sufficient support to keep the strings off the surface of
the soundboard.  Any help would be appreciated.

 

Frank Emerson

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://ptg.org/pipermail/pianotech.php/attachments/20100714/40679678/attachment.htm>