Re; Helper springs WAS Re: Key Leads and Inertia

[Bill Ballard]

At 8:23 AM -0700 6/14/03, David Love wrote:
>I can't comment from real scientific data, but I have never liked the feel
>of assist springs when they are tensioned above some undetermined amount
>(say, 10 - 15 grams which is typically the level at which they are used),
>if at all.  I am suspicious of the disconnect that they create between key
>and wippen with the assist spring always pushing the wippen away from the
>key.  Any bounce in the hammer off the rest rail (something that they also
>contribute to) will enhance this disconnect.

Figure a hammer weight at #1 of 7.5 to 13.5g, multiplied by~ a 7:1 
shank ratio would feel like to 95g measured at the knuckle. the 
uplift of the spring on the the wippen could be measured at the jack 
(at the knuckle, really), and compared to this (the positive figure 
with the spring attached, and the negative without the spring).

>My hypothesis is that an
>assist spring will work best when used in conjunction with a rocker arm
>capstan arrangement in which the key is directly linked to the wippen.

I would suggest that the helper should be applied to the driven lever 
(the shank on the way up and the key on the way down) and not an 
intermediate lever (the wippen in both directions). If the driven 
lever can be the restrained one, then the chances of it becoming 
uncoupled from the levers driving it on the return is kept to a 
minimum. Actually, as the hammer and wippen return to the starting 
position, the spring is offering its maximum resistance to the 
hammer's motion, and is in its best position for damping the hammer's 
return motion.

The coupling issue would seem to come down to that requirement, that 
the helping (or impeding, on the return trip) be applied to the 
driven lever. What I'd like to know is, if the helper springs really 
make the SWs seem smaller, how is the dynamic  behavior of a spring 
balanced action different from one with  simply, equivalently light 
hammers. (Obviously I'm not interested in the sound of a hammer which 
is 10-15g lighter; practically it doesn't exist.) The coupling 
differences of springs and magnets aside, I believe they would behave 
similarly, directly and immediately reducing the force of gravity, 
and to the extent that we removed FWs whose work was now being done 
by helpers, reducing the force of inertia.

I think that would be worth a couple of oatmeal cookies.

Bill Ballard RPT
NH Chapter, P.T.G.

"No one builds the *perfect* piano, you can only remove the obstacles 
to that perfection during the building."
     ...........LaRoy Edwards, Yamaha International Corp
+++++++++++++++++++++