Adjusting wippen assist springs

[Richard Brekne]

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Ok Mark... looks like the discussees were not 100% on the same page afterall...... but close enough I think. You in anycase answered
this first question I put forward. However... you end with...

         "With an assist spring to change the 60g action to a 40g one I would expect the sprung action to feel lighter at all
     levels."

Which goes right to the heart (at least the left side of it) of my second query.  Let me put forward a concrete example for you (and
whoever else) can perhaps use to clear up my question.

We have a single key action in front of us that can be set up two ways. Identical in every possible way except that on the first the
counterbalancing is done with lead, and on the second the counterbalancing is done with spring. Both set up to achieve an end BW of 40
grams(spring engaged).  Both with 10 gram SW, and 10 gram WBW( comprised of a 0.5 KR and 20 gram WRW) , and equal Strike Weight Ratios.
Further lets stipulate that the counterbalancing in the case of the leaded key is  20 grams of FW with 30 grams of lead evenly
distributed about the midpoint between the balance rail and the key front and 5 grams of FW in the form of the keys own mass, and in
the case of the spring assist, the spring is doing that exact same amount of work  as the lead to achieve the same static balance
weight (40 grams). (Ignore for the time being that the required spring tension will be in excess of what we have been saying should be
a maximum )

Using Stanwoods Balance Equation

(BW + FW - WBW) / SW = R

we have for the key leaded key then...

(40 + 20 - 10) / 10 = 5.0

and for the key with the assist spring

(55 + 5 - 10) / 10 = 5.0

(note we need a 55 gram BW without the spring engaged to end up with the same 40 grams BW when the spring is engaged)

The spring will help up to and including the equivalant of 15 grams of frontweight... that means its relieving 30 grams of weight at
the capstan.

-------

Now... if the spring assist action is to play lighter regardless of how hard you play, then that means that the influence of the spring
is always greater then the net result of the lead. Lets confine ourselves to levels of play that are below the 9.8 m/s^2 mark first ok
? Up to that point the influence of the lead weights is in the positive direction... ie...making the touch less <<heavy>>...
assisting.  If the springed counterbalance is always lighter...then its influence on the touch must continue beyond this mark...yes ??
So... how is that shown to be true... whats the physics/math behind that ?


Finnally an aside observation.... if what Mark and Sarah are saying is true... then aside from any need to increase key inertia for
whatever purposes... it would seem that in general. the lower the key inertia the better..... or that at least some minumum level of
key inertia should be identifable as a near constant for reasons that have nothing to do with touchweight per se'. Which in turn would
mean that the FW of all keys could be uniformly alligned to that value, and Stanwoods equation becomes then

(BW + K - WBW) / SW = R

where K is the constant FW.


Getting somewhere again with all this !! I love it :)

Cheers
RicB


Mark Davidson wrote:

> >RicB wrote:
>
> >But ok... assuming we're all on the same page, and I'm out to lunch again... then I guess what you are both saying is that given 2
> actions one >counterbalanced with lead to a 40 gram balance weight, and the other lead free with a resulting 60 gram balance
> weight... that the 60 gram >action will play lighter as long as you are accelerating the keys past the 9.8 m/s^2 mark.
>
> Not quite what I meant.  I think the assumption was that you replaced some lead with an assist spring. "Same force" implies you
> replace the force provided by the keylead with force provided by a spring.  So you have the same BW, but less mass in the key.  The
> case you give above I would expect the 40g action to be lighter in soft playing and the 60g action to feel lighter in loud playing.
> With an assist spring to change the 60g action to a 40g one I would expect the sprung action to feel lighter at all levels.
>
> -Mark
>
> _______________________________________________
> pianotech list info: https://www.moypiano.com/resources/#archives

--
Richard Brekne
RPT, N.P.T.F.
UiB, Bergen, Norway
mailto:rbrekne@broadpark.no
http://home.broadpark.no/~rbrekne/ricmain.html
http://www.hf.uib.no/grieg/personer/cv_RB.html


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