Hi folks Got done with a couple reads of Bobs article and thought I'd post some thoughts. I dunno if its of interest to the present crowd on either list but here goes anyways. Bobs experiment as it is presented in the first article concentrates on the first case scenario from Birkett's article "Static and Dynamic Balancing of a Piano Key" 2003 and the experimental results Bob gets compare very nicely indeed with the theoretical predictions from Dr. Birkett. Essentially what Dr. Birkett refers to as the dynamic breakpoint between soft and hard zones is exactly what Bob finds experimentally. Note, Dr Birketts "soft zone" is the degree of acceleration that can be shown to be aided by key leading, and the "hard zone" is the degree of acceleration where keyleading can be shown to be an impediment. The dynamic breakpoint is where the key mass (leading) either aids or impedes acceleration. Bob mentions that his measured data results in somewhat curved lines and seems to find this significant as compared to the straight lines in the theoretical model. I would think that Bobs results are to be expected in any system, either his pulley system or the real piano. Dr. Birketts model is straightforward and is meant to simply demonstrate the basic principles and results from a theoretical standpoint. What is of import here is the dynamic breakpoint itself more then whether there is a slightly non linear behavior (or not) to graphed accelerations for keymass and input force values. What at this point Bob seems to have missed is that the dynamic breakpoint is movable. Much of the rest of Dr. Birkett's paper goes on to show that if the key is balanced (counterweighted) at points closer to the fulcrum, then the dynamic breakpoint moves upwards on the graph. Essentially the placement of the breakpoint is not a simple function of the mass added to key... but how much mass is added where. Dr. Birkett provides a formula for accurately calculating all these relevant moments.. i.e. breakpoint location, slope of change in acceleration for change in force, etc. for any combination of both amount and location of what is essentially Stanwoods FW component. Using Bobs device, if one was to take his 5 added weights and measure them in terms of Front Weights, and then transpose this amount of FW to a point in between the key front and the balance pin hole (fulcrum) repeating the rest of his experiement then one would find the breakpoint moved so that the area of acceleration that is aided by the key mass is significantly enlarged. This basically confirms the idea behind the accelerated action. Indeed, Dr. Birkett states at one point: "Adding lead to the key closer to the fulcrum enlarges the soft zone. Moreover, there is less difference between the dynamic slopes for various static balanced conditions, i.e. the key behaves more like the unleaded key" I'll be interested to see what the follow up to this first article from Bob concludes. And I'd also like to see him expand his experiment in the fashion mentioned briefly above to see what comes out of that. Cheers RicB The other thing was an interesting article by Bob Hohf which touches on some core points of one of the best discussions through the 10 plus years I've been on CAUT/Pianotech... namely the dynamic touch weight discussions surrounding Dr. Birketts paper on same available on the internet. I'll do a couple good reads before commenting on it... but I can already see its highly recommendable to one and all. Cheers RicB
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