Key Leads and Inertia

[Mike Spalding]

David,

Here's 2 cents from a former engineer.  Engineering does depend on accurate
calculation, but depends equally on observation and classification,
otherwise known as putting things in perspective.

It would be unusual, in a complex system such as a piano action, for any one
parameter to be so overshadowed by the other parameters that it's effect
could be considered "eliminated".  The overall touch of a piano action is a
complex soup of many ingredients.  It doesn't take much pepper to change the
character of a soup.

True, if you run the numbers, you do find that the key lead inertia is less
than one-tenth the inertia of the hammer, shank, and wippen, as experienced
at the pianist's fingertip.  BUT - and here's where the putting it in
perspective part comes in - I would expect the key lead inertia to feel very
different to the pianist than the hammer/shank/wippen.  H/S/W inertia is
coupled to the finger through some very compliant elements:  whippy shank,
cushy knuckle, cushy wippen cushion, whereas the key lead is rigidly
coupled.  Remember Sarah's explanation of impedance matching?  H/S/W inertia
with compliant coupling should feel like kneading bread; it's the "depth" of
the keyboard.  Keyleads, on the other hand, should feel like impact.  Even
though the keylead inertia is quanititatively small in comparison, I expect
it is qualitatively significant due to it's direct coupling.  This would be
the challenge in Stephen's project to develop a dynamic model of the action:
to quantify how the compliance, or lack thereof, is experienced at the
pianist's fingertips.

The other possible way in which the numerically small keylead inertia could
significantly effect the pianist's experience is in trills or rapid staccato
playing where the key spends a lot of time not in contact with those other
large inertias.  Again, Stephen's dynamic model should be able to tell us a
lot about this situation.

Sorry, no hard answers, but at least some possibilities.

Mike Spalding RPT


----- Original Message -----
From: "David Love" <davidlovepianos@earthlink.net>
To: "Pianotech" <pianotech@ptg.org>
Sent: Friday, May 02, 2003 1:48 AM
Subject: Re: Key Leads and Inertia


> I'm not an engineer and will have to defer to those who can comment on
this
> in a more informed way, but your reference to the key doesn't change my
> point.  Movement of the key is being resisted by a variety of factors the
> would eliminate any significant effects of momentum in key travel, or so
it
> seems to me.
>
> David Love
> davidlovepianos@earthlink.net
>
>
> > [Original Message]
> > From: Richard Brekne <Richard.Brekne@grieg.uib.no>
> > To: Pianotech <pianotech@ptg.org>; <davidlovepianos@earthlink.net>
> > Date: 5/1/2003 10:59:41 PM
> > Subject: Re: Key Leads and Inertia
> >
> >
> >
> > David Love wrote:
> >
> > > It seems to me that because everything resists being moved (inertia)
> that
> > > acceleration probably takes place through the entire key stroke.  I
> would
> > > guess that the first mm of movement doesn't achieve much for the
reasons
> > > that have been  discussed, namely the flexing, compacting of various
> parts.
> > >
> > > David Love
> > > davidlovepianos@earthlink.net
> > >
> >
> > We were talking about the acceleration of the key itself David, the
> actions
> > compliance as a whole is a seperate issue, albiet a good one. Of course
> > acceleration / or deacceleration occurs through the whole key stroke,
> (except
> > perhaps very rarely... what a steady touch tho eh ?). But the presence
of
> > acceleration does not simply eliminate the affect of any momentum, and
> that
> > seems to be what is being said.
> >
> > The applet I sent a link clearly showed that all other things being
> equal, a
> > given mass halfway along the key would accelerate faster then half that
> amount
> > out at the end for the same downward force.
> >
> > I put 100 grams on the "rope" as it were, and 250 on the left side edge
> of the
> > "platform". Then ran the applet first with 250 grams at the right side
> edge of
> > the platform, and then 500 grams half way in on the right side. This
> resulted in
> > a faster acceleration for the 500 gram configuration. The 100 grams
> pulling at
> > the rope is the input force here, and the "platform" is the key. Only
> > significant detail missing relative to the inertia question isolated
from
> all
> > the other stuff thats being mixed in, is the orientation of gravity
here,
> as the
> > "platform" rotates horizontaly. That however, just takes gravity out
> (more or
> > less) of the picture in the demonstration.
> >
> > Its all part of a link to an online physics resource. Good for clowns,
> Steinway
> > enthusiasts, and Wissner lovers everywhere :)
> >
> > Cheers
> >
> > RicB
> >
> > I'm off for a weekend of camping. See you all on monday !
> >
> > RicB
> >
> >
> >
> >
> >
> >
> >
> > --
> > Richard Brekne
> > RPT, N.P.T.F.
> > UiB, Bergen, Norway
> > mailto:rbrekne@broadpark.no
> > http://home.broadpark.no/~rbrekne/ricmain.html
> >
>
>
>
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