Inertia

[Ed Sutton]

John Hartman wrote:
>
> I figured the MOI for the three action parts of a typical note. The
> hammer was 8 gms and there were three leads in the key. The front arm of
> the key was 25cm and action leverage was 5.3/1 with a BW of 35gms. Here
> are the number for the MOI as adjusted for reflected MOI:
>
> Key MOI = 10,307 gmcm^2
> Wippen MOI = 3149 gmcm*2
> Hammer and shank MOI = 165,528 gmcm*2
>
> There may be many virtues for keeping leads out of the keys but I can't
> see how it makes very much difference to the perceived weight of the
> action.

Similarly, using Jim Ellis' simple velocity formulas, I calculated that with a 12
gm hammer head, and 48 gms of lead (more than any of us are likely to use!), with
the leads magically compressed at 1/2 distance of the key from the balance pin,
the force to move the leads would be 1/25 of the force to move the hammer head
(all other factors omitted).  If the leads were magically compressed to be at 1/4
of the key length from the balance rail, the force to move the leads would be
1/100 of the force to move the hammer.

These are simplified and exaggerated results because
    1) All other parts weight are omitted
    2) The front weight is excessive
    3) It would not be possible to compress the leads to a single point, so that
in practice one could not make such a significant change in the location of the
leads.

This leads to the question of whether a pianist could discern a difference in the
order of 1/100th, 1/50th, 1/25th of the total force needed to move the system and
make a sound of a given intensity.  And how might we test this empirically?

One of the claims of the Magnetic Balanced Action is that the key lead inertia is
removed from the system.  This is certainly true, but is it significant for
performance? A blind comparison between two Fazioli pianos with identical
downweights, one with key leads, one with MBA would be the way to test this.  (A
performer friend who has played the MBA is convinced he can feel the "lack of
inertia."  However, I have felt a similar ease and sensitivity in a standard
Fazioli, so I am not yet convinced what he feels is the result of removing the key
leads.)

Or might it be possible to install a few MBA keys in a standard weighted piano,
adjust them to correct downweight, and see if the performer can detect them, and
how?

Again I suspect that the difference would be in speed of repetition.

So, Jim, we're looking forward to your experiments in jack reset time!

Ed Sutton