David L said: <The question at hand has to do with what exactly is the after touch spec that's used to make the formula ratio by product of the levers equal to the blow/dip ratio as given. (and) <But when I input those numbers in this calculator, as you can see, then by that formula a 5.75 AR with 45 mm of blow distance should regulate with 8.6 mm of dip. This illustrates the confusion I find in these formulas, if they are to be used from a design perspective rather than as a ballpark reactive position in the field. I feel the (blow distance-let off)/key dip-aftertouch) part of the equation, when compared to the lever arms part of the equation is apples to oranges. The lever arm side of the equation looks at the lever arms as the product of fixed ratios. However, the blow distance ratio does not look at blow distance and key dip as fixed ratios, but rather inputs arbitrary letoff/aftertouch as necessary to make that side of the equation match the fixed ratio side, as I think you've noted, David. Or seen another way, if you are going to use the blow distance side of the equation as given, then the lever arm side must take into consideration the whip's changing leverage and the shank's changing leverage during letoff. This changing leverage presents difficulties that would require computing complexities way beyond simple algebra. Taken in this light, your shy 8.6mm dip could be more a result of blow being quantified artificially. According to the fixed leverages, blow is not the distance between hammer at rest and the strings minus letoff, but rather (Full unimpeded travel of the hammer with out any letoff or strings) = Action ratio*(key dip-aftertouch). By the way, my comment here is not that this formula doesn't empirically work, but rather that the thinking behind it seems to be selective and thus confusing, at least to me. Jim Ialeggio -- Jim Ialeggio jim at grandpianosolutions.com 978 425-9026 Shirley Center, MA
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