<html> Hi Del,              Nice drawing, kind of in line with some of my ideas of theoretical centreing of bridges for grands.  What we tend to forget is that, the vibrations spread out from the bridge like a pebble thrown into a Mill pond. In a grand, because of the strike line and the position of the belly rail, the bridge is far from centred.  Some of this problem may be alleviated by varying the rib height. Thinner to the short side, taller to the long side. The design of the case and action position of vertical pianos will always give more flexibility than in a grand.  The thickness of the belly rail joint ( reflector ) to the board in the top treble is going to be a problem, along with where the bridge is fixed, vs the hammer line.  Lots of tap dancing is done in the extreme treble to get  better sustain, duplexing, undercutting the bridge,etc.  Ever tried putting an apron up there? I know off the wall.mmmmmmmmm  Shoot me I am being revolutionary. With accujust  hitch pins to reduce board loading in a controlled manner, along with an apron, and finally a variable height rib, we could theoretically centre that bridge.  Sunday musings. Roger   <blockquote type=cite class=cite cite>Good (no, excellent) explanation so far. But it's not any super-secret shape--though it is patented--and it has been pretty well developed. A jpg drawing of the soundboard assembly as used in our upright is attached. Del _______________________________________________ pianotech list info: <a href="https://www.moypiano.com/resources/#archives" eudora="autourl">https://www.moypiano.com/resources/#archives</a></blockquote> </html>