<HTML><HEAD> <META http-equiv=Content-Type content="text/html; charset=windows-1252"> <META content="MSHTML 6.00.2715.400" name=GENERATOR> <STYLE></STYLE> </HEAD> <BODY bgColor=#d8d0c8> <DIV><FONT face="MS Sans Serif" size=2>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?</FONT></DIV> <DIV><FONT face="MS Sans Serif" size=2></FONT> </DIV> <DIV><FONT face="MS Sans Serif" size=2> <DIV>David Love</DIV> <DIV><A href="mailto:davidlovepianos@earthlink.net">davidlovepianos@earthlink.net</A></DIV> <DIV> </DIV></FONT></DIV> <DIV> </DIV> <BLOCKQUOTE style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #000000 2px solid"> <DIV style="FONT: 10pt Arial">----- Original Message ----- </DIV> <DIV style="BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: black"><B>From:</B> <A title=pianobuilders@olynet.com href="mailto:pianobuilders@olynet.com">Barbara J. Fandrich</A> </DIV> <DIV style="FONT: 10pt arial"><B>To: </B><A title=pianotech@ptg.org href="mailto:pianotech@ptg.org">pianotech@ptg.org</A></DIV> <DIV style="FONT: 10pt arial"><B>Sent:</B> 3/29/2003 8:03:21 PM </DIV> <DIV style="FONT: 10pt arial"><B>Subject:</B> Bridge dimensions</DIV> <DIV><BR></DIV><FONT size=2> <DIV><FONT size=2>David Love wrote:</FONT></DIV> <DIV><FONT size=2></FONT> </DIV> <DIV><FONT size=2><EM>Del:</EM></DIV> <P><EM>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. </EM></P> <P><EM>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...</EM></P> <P>----------</P> <P>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. </P> <P>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. </P> <P>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.</P> <P>Del</P></FONT> <DIV> </DIV> <DIV> </DIV> <DIV><FONT size=2>Delwin D Fandrich<BR>Piano Designer & Builder<BR>Hoquiam, Washington 98550 USA<BR>360.532-2563<BR>360.532-6688<BR><A href="mailto:pianobuilders@olynet.com">pianobuilders@olynet.com</A></FONT></DIV></FONT></BLOCKQUOTE></BODY></HTML>