What's all this I hear about Inertia ?

[Richard Brekne]

Hi Fenton


    Ric,
    With Assist Springs. If the assist springs take 18 grams off the
    back of the key, that moment value as it relates to key ratio may be
    removed in lead from the front of the key. Nothing is changed except
    an amount of lead is replaced with a spring. Now, a before and after
    comparison can be made of the 'fell' of the action. BW will be the
    same, perhaps friction will be reduced slightly by less weight on
    the capstan. All of these experiments on my part were simply my
    mistakes that required a re-do, best opportunity there is for knowledge.
    Fenton

Agreed as far as it goes, tho you do change the key inertia quite a 
bit...  which several have offered opinion on. The only two formal 
studies I know about the affect of key ratio are Dr. Stephen Birketts 
treatise on the matter ( 
http://www.pianostemmer.no/files/key_balance.pdf ) and Bob Hohfs 
empirical experiments that bark up the exact same tree about half way up 
and echo Stephens results quite nearly exactly. The effect of key 
inertia / key mass on dynamic touch is quite interesting. The math in 
Birketts paper requires a bit of study unless you are adept... but with 
a bit of work most who have dug through their high school pre calculus 
and physics stuff should be able to make sense of it easy enough.

Cheers
RicB