Hi Will, The way I see it, you have an ideal string plane that is level and parallel to the keybed across the compass and down the string longitudinally (prior to being offset by the bridge). The design spec for string height is directly related to the ideal action geometry via the strike point, hammer bore, center coordinates, parts' geometry, key proportions, entrance height etc. ie change one, change all. So now it depends where you want to start redesigning this thing. First, we know Steinways are designed with a string height of 7-1/2" or 191mm. It is typical to see them dip down in the high treble to 189 or 188. I would correct this if I could to level the plate out from bass to treble allowing for some upward bowing in the tenor section and minor discrepencies that cannot be corrected without refitting the capos. Now imagine your ideally level longitudinal plane being parallel to the top of your bridge. Insert the bridge and you have two angles formed that together make up your downbearing. This composite angle of 0.5 to 1.5 degree angle is barely perceptible and changes ever so slightly, depending on the ratio of the speaking length to the backscale and changes to the bridge height and counter bearing height. I'm not BTW taking into account any changes this will introduce to the load. The further the bridge is from strikepoint, the less any minor changes in bridge height will have on the string height. In addition, the shorter the backscale relative to the speaking length, the greater that rear bearing angle will be. Thus you may be able to make your plate height adjustment at the back to accommodate a taller cap without affecting the string height. If you're going to change the string height, do so purposefully, knowing all resultant changes. As for spruce roots, I'm not sure speed of sound is a factor in range of human hearing as far as I know; although I don't doubt they sound different. Not to mention that any inherent stiffness in additional height is easily mitigated by the material. Jude Reveley, RPT Absolute Piano Restoration, LLC Lowell, Massachusetts (978) 323-4545
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