Crown without soundboards

[Anne Beetem]

>Hi Ed:
>
>When one considers a piano soundboard with many splits and there is
>still downbearing, one might think that indeed the ribs are supporting
>the downward force of the string bearing. However, when one also
>considers the fact that as humidity increases, the soundboard rises and
>increases the tension on the strings, one might think that the board is
>the crown supporting member. It is well known that the ribs do not
>lengthen any to speak of when the humidity increases, but the soundboard
>certainly does swell and rise with humidity increases. Perhaps we can
>gain a little more insight from the harpsichord builders who have to
>work with much fewer ribs and funny wavey things that go on with the
>soundboards.
>
>Jim Coleman, Sr.
>
  Well, it's a bit difficult to compare as harpsichords do not have metal
plates to stabilize the case.  As  a result the case also fluctuates to
noticeable effect with weather changes.   In the dryness of winter, the
soundboard may effectively rise in relation to the string band due to the
movement of all the parts of the instrument.   On the other hand,
instruments built in dry conditions which then have to adjust to very humid
conditions may develop a rippled board if ribbing is inadequate.   The ribs
do help control the flatness and stability of the board.

  There is no crown built into a harpsichord soundboard.  The ribs are flat
where they glue to the board.   Harpsichord and clavichord boards will work
quite well even when bowing down as long as there is still sufficient
downbearing.      As noted, there are far fewer ribs, these being
concentrated in the center region, though the pattern depends upon the type
of instrument.    Cracked boards are very common due to shrinkage under
conditions drier than at installation time.  A few slender cracks do not
seriously affect the instrument either.

  So, I don't know if that was very helpful.

  Best,  Anne








Anne Beetem
Harpsichords & Historic Pianos
2070 Bingham Ct.
Reston, VA  20191
abeetem@wizard.net