Just a quick comment on thinking about soundboard stiffness from an infrequent posting occasional lurker. I recently did some computer modeling of soundboards with sinusoidal inputs and one thing this did is help me understand what "stiffness" means in terms of the board and the impedance it presents to the vibrating string. It was something I had not thought of before I "ran some numbers". It should be noted that stiffness of the board in terms of static stiffness supporting the string bearing is very different than stiffness presented by the board to a vibrating string. Take a note in the "killer octave for example. When the string starts to vibrate the board at these frequencies, the wavelength in the board is on the order of a few inches. The string does not "care" or "see" how long or how big the board is underneath it. At these frequencies, it is only the stiffness and mass of the board in a small area around the string that counts in terms of what impedance the board presents to the string. Think of it as dropping a pebble in a pond. The waves move out from the initial point depending on the density and viscosity of the water in the area you dropped the pebble in. If the wavelength is 3 inches, the waves don't care if there is a "stiffer" fluid 2 feet away. Yes, there are reflections from shore (the edge of the board) that come back, but when they get back to the area that the pebble was dropped they will take on a form based on the conditions at that point. Of course, beefing up the ribs in this area to better support bearing in the region (which is as Ron and Del frequently point out -- a real problem in most pianos) will affect the stiffness in the area at the board frequencies as well and you will get the result you seek. In some cases, however, equating the static stiffness of the board with stiffness under vibration can lead down the wrong path or at least can cause you to focus on the wrong thing. One example would be to watch that the feathering of the ribs does not come so close to the bridge as in many Steinways (and others). In terms of Ron O's concern that centering the bridge between the belly rail and rim would lead to waves hitting the edges and bouncing back to meet at the bridge and cancel each other out. All I can say is that if you look at all the reflected action of a board in motion, you cease to worry about such things. What counts is to just have a stiff and massive edge to the board that cleanly terminates and reflects the boards vibration as Del and Ron so frequently point out. Scott Kuhn PTG Associate Houston, Texas
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