Key Leads and Inertia

[Richard Brekne]

Bill Ballard wrote:

> At 6:00 AM -0400 6/13/03, Mark Davidson wrote:
> >So far I like David's point best, that 85% of the energy goes into the
> >hammer.  That means a 10% variation in key inertia becomes only
> >a 1.5 variation in ....something.  Need more coffee.
>
> Went to re-heat my coffee. Let me toss this in. Of the three main
> force in a piano action, friction, gravity and inertia, friction is
> the only opposing force which actually removes a significant portion
> of energy from the system. Both gravity and inertia store and return
> an appreciable amount of energy to the system on the return stroke.
> Lift the hammer up and when you remove your finger from the key,
> gravity is there to make the parts swing back down. With inertia, the
> extra force required in lifting a heavier hammer is stored as
> potential in the parts' angular momentum. When the stroke slams to an
> end, the rotational kinetic energy is transferred to the string (and
> the mass of felt fibers) and is promptly reflected/returned to the
> parts.
>
> When energy is lost to friction, that energy is actually only
> converted to heat. In a piano action, we don't see a whole lot of
> thermal energy converted back into kinetic.

I think... we are << loosing >>  far more energy due to compliance
problems. Inertia also seems to have somewhat of a Breaking affect, similar
to friction. Too little key mass and the thing simply feels like a piece of
balsa wood.

Take a simple teeter totter down to a small scale. Balance a piece of wood
2 mm by 10 mm by 200 mm on a fulcum and see how it feels to the touch. Then
add say 10 grams of lead to both sides to keep it balanced.

Myself... I like the feel of a bit of substance there. Of course when
things go to extremes in the opposite direction... too much mass... the
points you make above become more and more relevant. Seems to me you've
sort of described in a way, the uselessness of making the action overly
massive. That relates to the hammers as much as the keys.

>
>
> Bill Ballard RPT
> NH Chapter, P.T.G.
>
> "Out here on the food chain, you either
>     diet,die, or dine"
>      ...........folksinger Mark Graham
> +++++++++++++++++++++
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--
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