Making a soundboard-S&S L board

[Erwinspiano@aol.com]

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In a message dated 11/12/2003 8:47:34 PM Pacific Standard Time, 
davidlovepianos@earthlink.net writes:
Based on recent experiences which have me viewing older soundboards with a 
degree of suspicion, the question I have is whether or not crown necessarily 
equates to stiffness.  If the issue with soundboards is whether or not they have 
adequate stiffness to create that opposing spring, is measured crown enough of 
an indicator?  In other words, is it possible that a soundboard may show 
adequate crown but not have adequate stiffness to perform properly when loaded?  

David Love
davidlovepianos@earthlink.net

      Dave
      It depends on how you define adequate. The answer to your last question 
is yes but more often no. I've seen very flexible boards with good crown that 
still had sufficient stiffness. An Ivers & pond 6 ft. comes to mind. It had 
short ribs but a . 400 thick panel & high tension scale. An awesome piano with 
amazing sustain. It seemed to depend on more panel stiffness. When strung the 
board was flat. And unloaded it sprung up a mile. It's less common to have 
good looking hemispherical crowned board that exhibits stiffness produce a bad 
sound, but it happens as you know. The sustain was like an organ.
   As one works with a variety of sound boards a good deal can be determined 
by a tactile sense about board stiffness. I didn't mention as to how stiff 
this L board was. It was very stiff. As stiff as any rib crowned board I'm 
accustomed to. 
    What do I mean? This will answer Crashvalves question as well. When 
pre-stressing a board with good legitimate crown values as I described, it does 
require having the plate in and secured with bolts & screws. Enough so that when 
driving the maple wedges between the struts and the bridge tops it (the plate) 
doesn't flex. Typical deflection values will be roughly 3 mm at the central 
strut 2 mm at the first tenor strut & 1 mm or maybe only .05mm at the top. The 
low tenor strut about 1 to 1.5. Glenn, these wedges are pushed in with my 
thumb while I'm pounding on the bridge top with my fist until it feels like I'm 
pounding on a gym floor which means it's very resistive to further deflection. 
The exception is the low tenor. It's not good practice to get overzealous here 
this very flexible & thinner corner of the board driven by more mass & so 
requires less bearing anyway.
  In more flexible boards you could drive them into reverse crown if not 
careful.Thes also usually have nominal crown. ie. 3 mm on the longest ribs 
unstrung. This to me is not crown These are the ones I'd be tonally suspicious of.
  Dale

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