Permanent Soundboard Crown!

[Farrell]

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Are you suggesting that the inner rim is taller at the rear left and =
front right corners of the case (referenced from the pianist sitting at =
the piano)? If the rim is at a constant height, i.e. within a plane, =
then how does the board form a cylinder as opposed to a paisley-shaped =
dome? If the edges of the board form a plane, and the board is taller in =
the middle than the edges, then you will end up with some form of a =
dome. And furthermore, I would suggest that if the middle of the =
soundboard is, let's say, 6 mm above the rim, then you will have 6 mm of =
crown as measured parallel with the ribs (crossing the middle) and you =
will have 6 mm of crown measured perpendicular to the ribs (crossing the =
middle). How else could it be?

So what is the difference between cylindrical crown and spherical crown?

Now of course the curvature of the soundboard perpendicular will be of a =
larger radii than that parallel to the ribs, but only because it has the =
same amount of crown over a greater distance (assuming we are not =
talking about a micro-grand).

Terry Farrell=20

I took "cylindrical curvature" to mean that the sheet is curved along =
the diagonal-ish line of the ribs, but flat as measured across the ribs. =
=20
=20
Trent Lesher

    Studies made by Bluthner research and development department have =
proven that tensions and compressions develop on the edges that are =
inhomogeneous and not controllable. In contrast, the soundboard that =
Bluthner has developed has a cylindrical curvature so that the tension =
of the soundboard can be exactly defined. The ribs are planed to fit the =
curvature needed and therefore the tension of the soundboard remains =
intact over the decades. In fact, even under difficult climatic =
conditions the curvature will remain in a constant form since not only =
the rib structure will hold it in place but also the red beech inner rim =
is preformed to the correct angle to receive and retain the soundboard's =
curve tension. Because the soundboard is pre-stressed in this fashion it =
can be fitted exactly and remain under curve tension permanently. The =
bridge, of course, is adapted to the tension and curvature of the =
soundboard in its optimum position. This ensures that string vibrations =
in their full spectrum are transferred to the soundboard. By utilizing =
the resonating surface, the special design of the Bluthner soundboard =
generates tone significantly better.=20

  The way I understand the above text, Bluethner uses crowned ribs and =
doesn't rely (at least not much) on panel compression to achieve crown.=20

  They want a cylindrical crown, as opposed to the spherical crown =
advocated by piano designers such as Klaus Fenner, who wants the board =
to be curved not only along the ribs, but also (roughly) along the =
bridge, with a high point at a certain location. Fenner favours =
compression-crowning and has some theories about stresses that need to =
exist not only in the soundboard, but also in the rim etc. to get a good =
sound.

  I've read both Klaus Fenner's and Ingbert Bluethner-Haessler's books =
on piano construction, that's how I learned about the differences.=20

  The text posted by Terry F. is pretty confusing when taken alone - =
probably because it is translated from German ;-)

   Calin Tantareanu
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   http://calintantareanu.tripod.com
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