Dear Ed and list: Thanks for your insights. Your perspective gives me a new understanding about what I have been doing with Steinway soundboards. By maximizing the compression, which is different from one board to the next, I see that I have tried to optimize the potential output of each instrument. Your're right, there is an art in the procedure of getting the load matched to the structure since compressing the board and planing the bridges with 2.5 degrees of front to back bearing does demand some measure of thoughtful consistency. The way to maximize the energy displaced by the board is to compress the board in the piano when setting downbearing by wedging the board under the middle plate strut until it is almost flat, simulating the loaded condition. Each board reacts differently, so if I were to use a predetermined equation, I think in many cases the end result would be less than the ideal amount of compression. What Steinway does then is a balanced relationship between downbearing and the strength of the arch. I dry soundboard panels to around 4.5% MC before pressing with flat sugar pine ribs into 54' radius cauls, then allow them to take on crown to 10 mm. measured along the longest rib before clamping into the rim for downbearing adjustments. Once clamped into the rim the crown is automatically reduced by half and then once loaded it will result in about a 2 to 3 mm. measurement of crown showing. This formula has been fairly consistent. The bevel on the inner rim is also an important consideration which I think averages around a couple of degrees. Yours thoughts about the coupling effect of case parts is well taken. In a similiar question brought up a few threads ago, concerning rim stress, Mike Mohr has told me that the rim on their instruments has never been intentionally spread to produce this effect. If anything he says it is just a natural by-product of the construction to have the sustain effect of the rim as described earlier. When the beam and keybed structure is comprised of spruce that is meant to provide residual resonance, it is difficult to scientifically measure the contribution of each. As a test, it is interesting to pluck the keyframe return spring and listen to the tonal quality and sustain that it produces. As spruce keybed rails age they should contibute more volume and sustain when this test is done. Well, thanks again for taking time last Saturday morning to contribute to the forum for what I think is great and valuable information. Brent ==== Brent Fischer, Piano Technician School of Music, Arizona State University Tempe, Arizona 85287-0405 602/965-6760 FAX 602/965-2659 Msg 602/965-3371 http://www.asu.edu/cfa/music/
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