ratio question

[A440A@aol.com]

I wrote: 
<< >Why is there is a distinct difference in feel between two actions that 
>achieve the same ratio with different knuckle distances?  Ie.  you can
arrive at the same overall action ratio with a 15.5 mm knuckle distance and a 
short
key ratio as you can with a 17 mm knuckle distance and a longer key ratio,
but the response of these two actions are NOT the same. 

"TW" Stanwood writes: 

>>Need more info to begin a discussion here... How do the Strike Weight
levels, Front Weight Levels, and Friction levels compare? These factors
effect response quality.<< 

    My statement was a general observation, not with a particular action in 
mind, so I haven't any SW or FW numbers to bring to bear.  
 
>>Do they both regulate to the same blow distance
with matching key dip?  (A difference in the distance-ratio/weight-ratio
ratio would indicate a difference in geometric efficiency between the two
actions.)< 

   I have had actions in the past that exhibited the same ratio with both 
knuckle distances, which is what brought on this concept.  Older Steinways, with 
15.5 mm knuckle distance performing at the same ratio as newer ones with the 
17 mm knuckle.  Blow distance was the same and dip was comparable,(since I use 
an aftertouch priority method of setting dip, I don't have a specific keydip 
spec. , but I rarely go beyond .400") 

>>How would you describe the qualitative difference in response
between these two actions? >>

   The shorter knuckle distance, coupled with the shorter capstan position 
seems to give a faster, more immediate feel to the action.  It is my vague 
belief that it is preferable on the smaller grands that use less SW.  The longer 
knuckle with the corresponding capstan placement to maintain the same ratio,( I 
find myself happiest with something in the 5.6 area) feels like "too much 
machine" on the smaller pianos, but usually gives a smoother feel on the large 
pianos.  
   Theses differences are not great, and with the tolerances encountered on 
Steinway actions, are subject to influence by more than a few other things.  
The short knuckles allow less room behind the jack after escapement, (even given 
that their use requires less movement of the whippen), so there is less 
flexibility in matters of blow/dip/aftertouch. As mentioned, their use compressess 
the timing of jack contact to let-off.           The position of the jack 
under the knuckle is also influences which set-up will feel best, too, and this 
begins to be dependant on the position of the whippen rail.  I haven't worked 
out the correlation of spread to the difference between the long action and 
short one, but I suspect that a relationship could be found. 
 
Ed Foote RPT 
www.uk-piano.org/edfoote/
www.uk-piano.org/edfoote/well_tempered_piano.html
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