We've seen quite a few 'second-tier' hypotheses - as Ric says, sexy explanations - for the backcheck phenomenon. These things obviously need to be examined experimentally, but a small dose of Occam might be a good thing first. I'm thinking something is causing this that occurs before the string impact. The obvious candidate is interaction between the backcheck and the hammer tail as the hammer heads toward the string. Backcheck clearance is supposed to be pretty tight, and I've seen enough examples of slight catching on the check as the tail goes up, enough that power is lost without it being obvious. For a given action configuration, this effect doesn't occur for all blows. It's a function of various action parameters, including softness of the whippen cushion and other felt contacts, hammer shank flexibility, tail geometry, and so on, as well as the type of touch applied to the key. Lowering the check to achieve the magic 2mm separation may very well ensure adequate clearance in all cases. It's probably possible to check this on a "dud" key before and after making the adjustment of backcheck height, even with just a bit of chalk on tip of the key tail. Static clearance of the check/key tail is certainly no guarantee of dynamic clearance. If it's too subtle for chalk it will need some targeted experiments with high speed images to investigate properly. From the current discussion, it seems the effect is also apparent if backcheck clearance height is too much more than 2mm, and the explanation above doesn't address that of course. To those who've had good results with Andre's technique (including Andre himself), in practical circumstances how often do the checks have to be lowered vs raised? Stephen -- Dr Stephen Birkett Associate Professor Department of Systems Design Engineering University of Waterloo Waterloo, Ontario Canada N2L 3G1 E3 Room 3158 tel: 519-888-4567 Ext. 3792 fax: 519-746-4791 PianoTech Lab Room E3-3160 Ext. 7115 mailto: sbirkett[at]real.uwaterloo.ca http://real.uwaterloo.ca/~sbirkett
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