Bridge dimensions

[Keith Roberts]

This is a multi-part message in MIME format.

---------------------- multipart/alternative attachment
The undercutting was to move the bridge /soundboard contact point away =
from the belly rail while maintaining the proper speaking length for =
notes in the high treble. There is not much flex in the board straight =
down from the front of the bridge in the last octave
Keith Roberts
  ----- Original Message -----=20
  From: David Love=20
  To: pianotech@ptg.org=20
  Sent: Saturday, March 29, 2003 8:34 PM
  Subject: RE: Bridge dimensions


  Perhaps it was a misinterpretation of your previous post on the =
subject, but I though you said that part of the reason for undercutting =
the bridge was to allow that part of the sound board to be able to move =
freely up and down.  That prompted my question as it seemed that freedom =
to move up and down and stiffness, i.e. high impedance, were at odds.  I =
think you've answered that question, but if the board is going to move =
anyway, why bother to undercut the bridge other than to move it away =
from the bellyrail?  Is it assumed that on a piano with a more severely =
undercut bridge, it should have a more substantial rib configuration to =
balance it and vice versa?  And given the choice between more mass in =
the bridge or more substance in the rib configuration, what would you =
choose?  Am I right in assuming that the more minimal undercutting in a =
Steinway bridge is because the rib configuration is more skimpy? ! If =
so, then would undercutting the bridge further on a Steinway create more =
problems and a weaker treble if the rib pattern and height remained the =
same?

  David Love
  davidlovepianos@earthlink.net


    ----- Original Message -----=20
    From: Barbara J. Fandrich=20
    To: pianotech@ptg.org
    Sent: 3/29/2003 8:03:21 PM=20
    Subject: Bridge dimensions


    David Love wrote:

    Del:
    Is there an ideal dimension (height, width and width at the =
footprint) in the treble section of the piano? It seems that the two =
requirements are at odds, one of flexibility to allow the soundboard to =
move, and one of stiffness to increase impedance in that section and =
improve sustain.=20

    Wouldn't it be better to support the board in that section with an =
additional rib, say, and leave the bridge more flexible? Or is it six of =
one...

    ----------

    It depends, I suppose, on what you mean by 'ideal.' Why do you think =
the bridge needs to be "[flexible] enough to allow the soundboard to =
move...?" The soundboard is going to move anyway--even if the bridges =
were infinitly stiff it (the assembly) would still move.=20

    The bridges need to be stiff enough so that the impedance level does =
not drop enough to significantly affect power and sustain in between the =
ribs. Obviously, if the ribs are closer together, i.e., a greater number =
of ribs, the bridge do not have to be as tall to accomplish this. Both =
the bridge dimensions and the number of ribs and their dimensions are a =
balancing act. The more ribs--and the more stiffness and mass in the rib =
field--the lower and less massive the bridge can (should) be. If the rib =
field is skimpy the bridges are going to have to be taller and wider to =
compensate.=20

    Bridge width is usually as much a function of mechanical necessity =
as of acoustics. It must be wide enough to easily accomodate the bridge =
pinning configuration without coming apart. It has been my observation =
over the years that bridges that are much less than 30 to 32 mm in width =
are somewhat more prone to splitting.

    Del



    Delwin D Fandrich
    Piano Designer & Builder
    Hoquiam, Washington 98550 USA
    360.532-2563
    360.532-6688
    pianobuilders@olynet.com

---------------------- multipart/alternative attachment
An HTML attachment was scrubbed...
URL: https://www.moypiano.com/ptg/pianotech.php/attachments/2d/00/d6/70/attachment.htm

---------------------- multipart/alternative attachment--