Greetings, Inre bridge wedging, Ted writes; >The theory was to cut down to the soundboard vertically under the struts, jack up the board and glue wedges in the saw kerfs. This is intended to increase the curvature of the of the soundboard. I never did it as every instinct rebelled against the idea, and later I encountered three pianos that had had this type or repair.Each one sounded very dead. I have to agree with Ted about the destruction caused by sawing the bridges. You may notice this treatment on key frames, I believe the technique is called a "Dutchman" cut. It does provide a restorative force in the direction mentioned, but there are greater implications on acoustical transmission. We understand the great difference in speed and efficiency of sound transmission between with the grain vs across the grain. I believe this is related to what happens to mechanical energy when it is transferred from one medium to another, and until that energy is moving our TMs, it is mechanical. As you go across the grain, the differing characteristics of the wood layers, ( what were "rings" in the tree), cause this transmission loss every time it goes from soft "summer wood" to hard "winter wood", ( though I accept Cliff Geers explanation that it is more like "spring" wood vs everything else). Sound traveling with the grain doesn't suffer these losses, as the energy travels with the grain without encountering varying densities . Thus, the bridge is the major component in transferring the sound to the board as a whole, ( with a lot of help from the ribs!!). Observe the effort put into the continual bridges that make the treble and bass bridge as one unit. This is not an easy manufacturing process, but the results are worth it when you have a large board to energize. Cutting the bridge, and inserting glue and more wood, effectively damps this transmission of mechanical energy. Richard asks; I wonder what holds the soundboard up? I have always considered there to be a circle of compression/tension set up by the downbearing force attempting to spread the crown, which is resisted by the containment of the case, which is assisted by the connection to the plate, which is compressed by the tension of the strings, i.e., the sound board is held up by its inability to spread out. Thus we have the Centripedal tension regulator of the Mason and Hamlins. The "perma-crowns of some older Wurlitzers, etc. Simply propping up the soundboard does not increase its response to vibration, though it may address rattling strings due to negative bearing. I know there are some out there that have a much more scientific explanation, but I am not holding my breath that our Steinway correspondants are going to tell all the secrets that make their piano soundboards so responsive. Regards, Ed Foote
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