"da Shadow" rote, 1/20/96:
>> the first big issue in touch resistence, namely, is your problem >>one of
friction or of mass.
>Don't we have to distinguish between three parameters, i.e. >friction,
static weight and dynamic weight, the last being >inertia?
While we're putting together the kitchen sink, why not throw in
leverage ratio (in practice, Strike Ratio). Strike ratio modulates the
unlevered WEIGHT of the parts. As I must gather from reading your post, the
"static WEIGHT" is that counterbalancing WEIGHT on the front end of the key
which is just enough to upset an equilibrium between the two sides of the
key, and put the entire system into a slowest of slow crawls in which the
heavier side of the key (now the front) gets to pursue its gravitational
attraction to the earth's mass. Since you didn't mention balance WEIGHT once,
I'll assume that for you "static WEIGHT" are the sibling down and up weights.
BTW, these combine friction and mass.
The "dynamic WEIGHT", I'll agree, is what you feel (and what you
describe in the post) with your fingers and arms. "Inertia becomes important
in fast play, as it seems more difficult to accelerate the key due to the
quantity of mass that has to be moved. When paired with a high down WEIGHT it
becomes almost intolerable." I'll also agree that this is inertia, but
inertia is more properly an attribute of mass, while WEIGHT is an expression
of gravitational attraction. But at the risk of having my high school diploma
revoked, I'll state that I'm not concerned with any conversion between WEIGHT
and mass when our observations move from the lever train's response to a dead
WEIGHT which barely tips the balance of the key (the "static"), to the
dynamic, ie.the lever's response to a finger/hand of widely varying
velocities (and velocity curves). I'm not concerned because the major player
in the gravity/WEIGHT situation is given to be a constant in our dialy
practice. (The major player is the earth's mass, the minor, the net mass on
the heavier side of the key.)
So, if I can alert you to a bottom line, my first distinction is
between friction and mass, only. For two reasons. First, the mass of the
parts in the system will show its effect in how it is distributed across the
fulcrum of the key (your "static WEIGHT"), and in how much inertial
resistence builds up in the sum of the masses on both side of the key
fulcrum. Also, the WEIGHT which appears in your observations at the front of
the key (down/up WEIGHTS) is a product of the lever train's Strike Ratio.
Granted that the WEIGHT in the system has its effect on friction, the effect
is minor when compared to effect a given change in mass (at the hammer, say)
will have in the domain of mass. All of these come under one heading and I
drop them all in one bucket.
The second reason that my first distinction is between friction and
mass comes from how we deal with this situation. A pianist (which I gather
you are) would deal with these problems by leaving a message on our answering
machine. We technicians, the ones doing the actual work, have to be careful
in addressing the problem. We need to know immediately whether the touch
resistence problem comes from friction or mass, and if it ceoms from mass,
whether that's from outsized strike WEIGHTS or strike ratios. Each of the is
dealt with differently, and we technicians hate to mis-diagnose something.
David Stanwood mentions spreadsheets. I use a charting/presentation app
which shows on one page, a graph of where friction and balance weight lie,
and another where strike weight and strike ratio lie. This tells me most on
what I want to know about an action's resistence.
<<That is, if the static weight (the down and up weight) is on spec we still
have to deal with the dynamic weight, or rather a product of the friction and
the dynamic weigth (inertia).>>
If the down and up are on spec, friction will not be your problem hear
as by definition friction will then be on spec, too.
<<Inertia becomes important in fast play, as it seems more difficult to
accelerate the key due to the quantity of mass that has to be moved. When
paired with a high down weight it becomes almost intolerable.>>
Yer darn tootin', pardner! Consider this. When ever the finger/hand
assembly and the action assembly are moving at different speeds, the slower
will present a pressure to the faster. (In most cases, it will be the human
being moving faster and the action which has to catch up with its speed.)
What happens when the finger at the pianist's desired speed meets up with a
lever train with zero velocity, ie. at rest. For the instant in which the
finger is going at its full speed and the key (et al) is at rest, the finger
might as well be pressing (or slamming) into a brick wall. That instant is
brief of course, as the key promptly accelerates to match the finger's speed.
During this acceleration, the "brick wall" fades into a soft pliable spring.
Why is inertia so important? Because as increasing amounts of mass
present increasing amounts of inertia requiring increasing amounts of energy
to get the mass of these parts rolling, it is inertia which determines how
quickly that brick wall turns from hard to soft. I don't know what the time
frame is for this "fade" (milliseconds, maybe?). I do know that "in fast
play", the duration of this fade becomes a greater portion of the finger's
interaction with the key.
<<The question could be what is the most decisive element when it comes to
the feel in the fingers, leaving friction aside, is it the static or the
dynamic weight? As an example what would be the difference in feel of the
two: a low down weight with high inertia or the other way around?>>
Tell us what part of the country you come from, and we'll see how soon
we can sit you down at a *spring-balanced* Stanwood Calibrated Action. In an
afternoon we could try several settings of friction and balance weight (your
"static weight"), the best way to answer your question. BTW, the spring
balancing has most of the work of counterbalacing action parts done by a
whippen helper spring, rather than leads on the front of the key. With the
key thus lightened, the action is incredibly quick to accelerate. (If it's
"frighteningly quick" we can remedy that with a tad more friction.)
<<Finally, what is the exact relation between weight and repetition? Is a
very light action invariably connected with slow repetition, maybe due to a
low up weight?>>
In height of play, a hammer's rebound from the string will blow right
past a low up weight. Ready for an anti-climax? Repetition is mainly in the
mechanical regualtion. The trickiest part of this is getting the check up to
1/8" below drop.
Bill Ballard RPT
NH Chapter PTG
"If we see you SMOKING we will assume that you are on fire and will take
appropriate measures".......Sign in a Music Dept. Hallway
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