Key Inertia

[Sarah Fox]

This is a multi-part message in MIME format.

---------------------- multipart/alternative attachment
Hi Mark,

Not sure if your post was directed to me or to others.  I do believe =
(and have argued before) that there are impedance matching issues =
between a pianist's arms/hands/fingers and the keystick -- or perhaps =
more accurately the entire action.  I remember visiting a friend who was =
interested to hear a piece I had been working on.  I played it for her =
-- on her spinet.  The piano was apparently well tuned and maintained.  =
But as I was trying to play the thing, trying to eek more out of it with =
each crescendo -- and as the keys were effortlessly bottoming and the =
piano just WOULD NOT put out anything more -- well, there were a few =
colorful phrases floating around in my head at the time to describe the =
fine instrument I was playing.  I'm sure the piano would have been great =
for the average 4-year old, but for me, there was a pretty awful =
impedance matching problem. (And yes, I realize there were also =
limitations from the longitudinally challenged strings and the =
short-of-stature soundboard.)

There are likewise actions that are too massive for me to play =
comfortably.  If I were a huge person, on the other hand, I imagine I =
would be able to play those actions with ease -- and my friend's spinet =
would seem like even more absurd a tinker toy.

The difficulty is not when a note is played softly/gently.  That's =
merely a force issue.  Any toddler can play a note gently on any piano.  =
Rather, it's an inertia issue that presents itself during more forceful =
and rapid playing -- when lots of key acceleration is required.  Instead =
of simply resting one's finger on the key and depressing it, one must =
fly at the key and "punch" it, bounding off of it towards the next key.  =
*That* is where impedance matching would become important.

Mind you, I don't really know how the mechanical impedance of an arm =
would be characterized and how it would best be matched to the impedance =
of the action, as referenced to the front of the key.  Perhaps our =
engineer friends could help us with that one. In the end, I would think =
it important to have some degree of impedance mismatch, to aid with the =
hand's rebound from the key.  If the action's impedance is higher than =
the arm's (which I would think would be an INCREDIBLY heavy action such =
as we've not built), then the hand would spring off of the tops of the =
keys.  If the impedance is the same, then there would be little or no =
"spring," and there would be a sensation similar to running in the sand =
-- maximum energy transfer per note, but too much "bogging" on each note =
to have energy to put into the next note.  If the impedance is lower, =
then the key would bottom, and the fingers/hand/arm would be able to =
"hop" off of the front rail.  If the impedance is too much lower, then =
there would be "nothing there" -- as with the spinet -- and playing the =
piano would almost be the effortless experience of "playing" one's =
dining room table -- or a toy electronic keyboard.  I suspect this all =
comes down to trial and error -- personal taste.  Perhaps some table of =
values could show average preferences, but I'm sure much would depend on =
the individual.

As for the center of percussion of the keystick?  New concept to me.  =
The concept makes sense, but I don't really know how to work with it.  =
(Alas, Freshling Physics was the extent of my education in mechanics.)  =
I would think the effective center of percussion of a loaded keystick =
(i.e. loaded with the top action) would be very close to the capstan =
anyway.  I doubt it would be possible to impart that much energy to the =
top action by a mere "bonk" on the keystick, absent of any other forces. =
 Put another way if the action were floating in microgravity, and if the =
key were not mounted in the keyframe, I doubt there would be much "play" =
from "bonking" the key into rotation against the wippen.  I'm sure it =
requires a deliberate stroke, corresponding to a prolonged upwards force =
of the balance rail on the underside of the keystick.  Thus the center =
of percussion of the keystick might be a moot point.  Dunno...  I'm =
curious to hear what our engineering friends think.

Peace,
Sarah

  ----- Original Message -----=20
  From: Mark Davidson=20
  To: Pianotech=20
  Sent: Thursday, December 18, 2003 9:00 PM
  Subject: Key Inertia


  So what about impedance matching of the key and hand/arm? Or the =
center of percussion of a key with leads, vs. without?

  There must be some touch issues there also, especially with respect to =
fast and hard playing.  Wouldn't center of percussion move closer to =
balance rail if springs replaced
  leads?  How would that affect touch?

  Thoughts?

  -Mark
---------------------- multipart/alternative attachment
An HTML attachment was scrubbed...
URL: https://www.moypiano.com/ptg/pianotech.php/attachments/6a/58/c0/ea/attachment.htm

---------------------- multipart/alternative attachment--