Inertia, was "Grand Touch"

[V T]

Hello Ed,

Your points are very valid.  The hammer creates the
bulk of the inertia.  I did the calculation a few
years ago, going through every part of the action to
account for inertia and came up with a typical
contribution from the keys/lead in the range of 20%,
and most of the rest of course from the hammer.  The
number changes as you move along the keyboard.

I once saw an action that had no lead in the keys - it
was balanced with magnets.  That means most of the key
inertia was eliminated.  Everyone who played it
noticed the difference.  Some loved it, some didn't.

Vladan

===================================
Ed Sutton wrote:

About 2 years ago this question was discussed at great
inconclusive length on CAUT.

Probably the most important question was "can the
pianist feel a difference?"

No one doubted that weight location could make a
difference in the moment of inertia of the key. But
the key is a small part of the system.  Other parts,
especially the hammer head, contribute their moments
of inertia as well.

The question becomes "What percentage of the total of
what the pianist feels can be changed by changing the
moment of inertia of the key, and what percentage is
controlled by the rest of the system? Is it enough to
matter?"

Take a look at Stanwood's lever drawing.

Note the 10 gram hammer at the end of the lever that
is 5 times longer than the key front. What is the
moment of inertia represented by that part of the
system?

Now look at the frontweight, 20 grams, at the front of
the "0ne unit long" key.

Change that to 40 grams at the "one half unit"
location.

That makes a big difference in the moment of inertia
of the front end of the system taken alone, but how
much change does it make in the entire system?  Is
this enough to change the performance response of the
piano a perceptible amount?

Ed Sutton

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