Rib Crowned Hamburgs ?

[Delwin D Fandrich]

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Dale,
 
1) I'd rather have the mass in the bridge and the ribs than have it all spread
out in the panel itself. (Think about it some to see the ramifications of this.)

 
How much mass is enough is dependent on the scaling. High tension scales
obviously need both more mass and more stiffness so you can use a panel that is
a bit thicker in larger concert pianos (but I still think anything over 8 mm is
probably too much). Lower tension scales need less of both. 
 
2) Yes I mean thinner. The thinner boards do seem to give up faster. There is
more unit force in compression. I've measured diaphragmed soundboards that were
more like 4 mm and 5 mm around the parameter (which is, I think, pretty close to
Steinway's specification for diaphragmed soundboards) and these are the boards
that seem to give up the fastest in extreme climates. 
 
3) Since you are not depending on internal compression to form and/or hold
system crown you can treat the soundboard panel as a non-structural member. This
means you can vary its thickness to suit your perception of what the soundboard
system need in terms of mass (and stiffness in the treble where the bridge's
proximity to the bellyrail extension becomes an issue) and not worry about how
thick it needs to be to form and/or hold crown.
 
Del 
 
 
 


  _____  

From: pianotech-bounces@ptg.org [mailto:pianotech-bounces@ptg.org] On Behalf Of
Erwinspiano@aol.com
Sent: June 23, 2005 7:44 AM
To: pianotech@ptg.org
Subject: Re: Rib Crowned Hamburgs ?



      Del
    Thanks for the perspective but what a bout an appropriate amount of mass in
this area adding to the impedance qualities? I realize the importance of rib
stiffness for this purpose but....how much mass is too much or not enough?   Too
much thickness in the treble can give a stingy sound  & too thin sometimes a a
sound not dark enough for my liking


Dale,
 
This is true only if the soundboard assembly is compression-crowned where the
thickness of the board is necessary to support crown over the years. It's why
diaphragmed soundboards collapse more rapidly than do thicker boards.

   Perhaps I'm misunderstanding your point here. Do you mean thinner, as the
compression load a on a thinner board would give up sooner. Also most
diaphramized bords are 8 mm or less around the perimeter
 


 
If the soundboard is crowned using curved ribs the bulk of the crown support
comes from the rib and the panel functions more as a non-structural diaphragm.
In this system the thickness of the soundboard is chosen based more on
(acoustical needs )and less on structural requirements and 8 mm is quite
adequate. 

 

would you elaborate on this

 
 

This is especially true if a reasonable cutoff bar and a fish are used.

  Yes I see this makes sense. Less area is automatically made stiffer
   Thanks
    Dale
 


 
Del




 

   Ron
  8 mm /.320ish is on the thin side for a 9ft grand of any make . A board this
thin doesn't really need much thinning. In fact it's probably not thick enough
in the treble. I'm unaware of the German factory's rhetoric on panel thinning.
I'm guessing it sounded a bit thin? grin
  Regards
  Dale

Very often the factory line doesn't match the actual product. How 
often have we heard about the tapering of sound board panels from 
S&S. They may have done it at some time but . . . The original board 
which I pulled from a 1962 Hamburg D last year had a 8 mm thick panel 
everywhere. I still have the original panel at the workshop.

Ron O.

 


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