Key Leads and Inertia

[Phillip Ford]

> > Ric suggests getting some real data:
> > >One point I'd like to get clear pretty quickly tho... just what
> > >level of play can we expect to be able to expand the so called soft
> > >zone too by configuring the keys intertia appropriatly ?.....
> >
> > Stephen B replies:  Sure. It wouldn't be too hard to estimate some 
> parameters for real
> > keys and actions...
>
>Ric B's rejoinder:  I did a little very informal playing around with a 
>digital 0-5 kg scale
>yesterday, and very very roughly, a light touch held the scale below he
>500 grams level, a medium touch certainly below 2000 grams, and you had
>to press reasonably hard to get 5000 grams pressure.
>
>If we start off with these very rough figures, and figure an "action
>weight" of 100 grams on a the back of the key, then the soft zone is
>going to pretty much be a pianisimo thing. Certainly by the time you hit
>a blow of 500 grams we would be in the so called hard zone... no matter
>which way you turn it if these assumptions are anything close to correct.

Now I'm getting interested in the ballpark in which this breakpoint plays for 'normally leaded' actions.  If it's down in the ppp range then all of this talk may be for nothing.  Shifting it around by changing lead locations might still not move the breakpoint out into the dynamic range that the pianist is using most of the time.


>One other point I am a bit unclear on. The article seems to say that the
>position of the breakpoint is independant of any key leverage ratio. The
>location of the breakpoint is given as a = (r/rb)g. rk is given to denote
>the distance from the fulcrum the <<action weight>> is applied to the
>back of the key. In each case this yields then also the amount of input
>force by the finger that is needed to achieve this breakpoint
>accelleration... also independant of the keys actual leverage...??
>Perhaps I misunderstand this ?
>
>RicB

The acceleration at the breakpoint is determined by the relative location of the lead to the finger force.  However the force at the breakpoint is dependent on key parameters.  You need both to locate the breakpoint.  I would think that Ik and rk are going to be dependent on the key ratio.  Changing rk changes the key ratio.  Changing rk also moves mass M changing the CG of the key and consequently Ik.

Phil F