Unusual rib structure?

[Sarah Fox]

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Re: Unusual rib structure?Hi Ron,

Thanks for the feedback.  Rib crowned?  Interesting.  What =
characteristics suggest that?  (I know very little about soundboard/rib =
structure.)  I gather that rib crowning is a more recent development in =
piano technology?  Is there some place I could read a brief history?

I measured the ribs for you.  I wasn't perfectly exact in my =
measurements (didn't have the time), but if you want more exact =
measurements, I'll get them for you later.  Aside from the tapered ends, =
the dimensions are constant throughout the length of each rib.  The =
bottom of each rib is rounded slightly   I didn't measure the lengths of =
the tapers.  The height and width of the ribs (in mm) are as follows (in =
order from treble to bass):

rib    h    w
1    difficult access
2    19    19
3    21    21
4    21    23
5    25    24
6    25    25
7    26    26
8    ?    26 (difficult access)
9    28    26
10    28    26
11    28    26
12    27    26
13    27    26
14    26    26
15    26    26
16    26    26
17   difficult access
18   difficult access

You are correct that the bass is rather dark.  Of course I like it that =
way.

Peace,
Sarah
  ----- Original Message -----=20
  From: Ron Overs=20
  To: Pianotech=20
  Sent: Tuesday, May 06, 2003 6:43 PM
  Subject: Re: Unusual rib structure?


  Hi Sarah,


  Its an interesting piano you have.


    OK, there's something about my piano (1933 Wissner 9') that seems =
odd (in my limited experience), and I've just got to ask.  My soundboard =
ribs have an unusual structure (I think), and I'm uncertain as to the =
purpose.  Most of the ribs are "tied" together with one of two small =
cross-braces.


  I can't see how the ties can do anything to either enhance the =
structure of the board or its function tonally. They remind me of the =
tie strap across the bass corner ribs of a model B Steinway, which also =
are of doubtful benefit.


     Counting from the keyboard, high treble end of the soundboard, the =
first brace starts around the center, keyboard-end of the soundboard at =
rib 8 and continues leftward and towards the tail through rib 13.  Then =
from the other end of rib 13 (right side of the piano), another brace =
starts and extends towards rib 17 in the tail.  Ribs 1-7 and rib 18 have =
no cross-braces.


  An 18 rib design, while the D has 17 in the latest offerings at least.


      Here are some photos:

    www.wonderfulhome.info/soundboard1.jpg
    www.wonderfulhome.info/soundboard2.jpg
    www.wonderfulhome.info/soundboard3.jpg


  Looking at what appears to be the fifth rib from the bass Sarah (the =
rib which in jpg 3 runs to the top LH corner of the image), the rib =
appears to be quite deep in the centre. They look suspiciously like they =
are rib crowned. Would you mind measuring the overall rib depths at =
their centres? I'd be interested to know what they are.



    The ribs on the cross-brace end are not smoothly tapered the way I =
think of most ribs being.  Rather, they are reduced in tiers, and the =
cross-braces run across the tiers.  The rib ends without cross-bracing =
are tapered in the conventional manner.

    So...  Why was this done?  Was it a way of stiffening the =
soundboard?


  I would speculate that the designer was interested in achieving a =
graduation in the sudden reduction of the rib section modulus of a =
conventionally feathered rib. The stepped feathering would probably =
cause the panel deflection to be somewhat more progressive. Mind you, =
this may not necessarily be desirable. For me at least, the 'jury is =
still out' on this matter.


    .  The bass on this piano is incredibly rich, powerful, and mellow, =
and the sustain is unbelievable.


  The tiered feathering should allow quite a substantial impedance =
reduction in the panel behind the bass bridge. I would expect this piano =
to have quite a dark tone in the bass.


  I'll be interested to hear other observations of others re the =
feathering.


  Ron O.


--=20

  _______________________

  OVERS PIANOS - SYDNEY
  Grand Piano Manufacturers


  Web: http://overspianos.com.au
  mailto:info@overspianos.com.au
  _______________________

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