At 9:35 PM +0200 10/15/00, Richard Brekne wrote:
>Newton Hunt wrote:
>
> > > the picture is more complicated that just these measurements
> >
> > You are absolutely right. My point was, and is, that those
> > numbers are where you _start_. There are many other factors
> > to account for but without understand David's system you
> > have almost no hope of coming to a "best" solution to an
> > action problem. It was not obvious to me from the early
> > posts that there was that understanding in place. Hence my
> > soapbox.
> >
>
>Grin... Newton... thats the point now aint it ?? that understanding is not
>in place... thats why folks like Terry and I ask questions. Not to worry
>tho... I am, and I believe Terry probably is also the type that will figure
>it all out sooner or later... no matter how many Bostons or Duysens we have
>to tear into. But it would be nice with a bit of dialouge beyond the
>obvious when such queries are posted. Grin... God knows I dont know enough
>about any of this stuff yet to be giving any solid advice...
>Stanwoods "method" is (cant possibly be) fundementally at odds with
>previous knowledge on the subject matter so there should be plenty things
>to talk about even for Stanwood licensees that doesnt breach his patent
>protection stuff. As far as I can see, Stanwood takes an approach to action
>geometry that is, shall I say, "weight priority" founded, instead of
>"lengths priority". And it does so to provide a more predictable way of
>achieving intended design results in a way that is more cost effective then
>present standard factory proceedure.
It's not at odds with previous knowledge and nostrums. It just
happens to be in a parallel dimension, the dimension of mass instead
of distance. Those basing their analysis on the length of lever arms
can generate all the 5-decimal place numbers they like. IMNSHO, we
should be in the dimension of mass, as has already been suggested.
When was the last time a pianist's response to a thoroughly
out-for-the-noon-hour action was that the keys were too shallow or
the hammershanks' inclination too steep. What they *do* say is that
the action is slow to respond (or conversely, flies away from them),
and that they simply can't get used to it or work with it.
What "it" is, is inertia. And the primary determinants are the weight
of the hammers mounted (SW), the overall action leverage ratio
(SBR), and how much heavier the back side of the key lever (BW) is
than the front half of the key (FW, and then some). The way actions
are usually put together, you start with the SWs (whatever the
factory's hammer dept. is sending out this week). This weight and
other weights below it are modulated by the overall action leverage
ratio (SBR), which in general is determined by the key and shank
ratios. The key ratio (wherever strike point C8 hits in respect to
the default location for the keyframe, and the shank ratio is the R&D
dept's choice of hammershank. The resultant rotational mass usually
weighs too much for comfortable playing and needs counterbalancing
with leads in the keys (FWs).
The key is the primary action lever, with the leads out front, and
the weight of everything else on the far side, most of it loaded on
the cap. The difference between the weights on either side of the key
fulcrum will certainly go down in the counterbalancing, but the sum
of the two sides (in fact the total amount of mass being rotated in
this machine) will also climb. Just as friction spreads the DW and UW
apart, inertia spreads the BW (the difference between key halves) and
the Total Inertia (their sum). In fact the total inertial weight is
neatly expressed by the FWs as what needs adding to the FWs is a
constant and a variable (a BW of your choice).
It comes down to this: If you're sticking (or stuck) with given SWs,
and can't do anything about the action leverage, and if one or both
of these are not favorable, you'll have to choose between a hoped-for
BW and whatever extra counterbalancing is required because of the
unfavorable SWs or/and the SBR. Believe me, most pianist's would pick
low inertia over low BW, if forced to choose. What we do is to tune
mass and leverage. If they are not properly matched, the piano will
be a poor mate, a dancing partner if you will, for the pianist.
To match them, you have to be able to measure them. The proper
dimension for me is the weight dimension. (Yes, I know the difference
between weight and mass, and I am specifying weight). David Stanwood
has a simple but very elegant system of measurement. Admittedly a
static one (not dealing with the moment of inertia and its
integrals), it allows us to watch how the weight of the hammers is
translated through the lever train, to see whether what the pianist
feels is within certain guidelines, and to know what needs correcting
and by how much.
I am very impressed by the studies and theories of technicians
working in the dimension of distance (of lever arms). But the length
of lever arms seems to me very much abstracted from what the pianist
feels. And I enjoy the most obvious elegance of the Stanwood system,
the fact that, excepting SWs most of the over-all facts about the
action are deduced by a weight measurement at the keyfront. Nice and
consistent.
I'm not even convinced of the importance of these "magic lines" (or
axes, as I belive engineers would prefer to call them). The
rep-center/knuckle-contact/hammer-center axis is simply unattainable
(excepting of course the old Aeolian shanks). And I became
disenchanted with the key-center/heel-contact/rep-center about five
years ago. I had moved a heel forward, and moved the cap line to
match, and was wondering whether I should use the Renner heel to
match the profile of the original (moving the cap-heel contact line)
over on a horizontal line, diverging from the key-rep axis. My other
choice was a taller heel which in the new forward position, would
drop the cap-heel contact back down towards the key-rep axis.
You'd think it would prefer the latter. You'd be wrong. Staying with
the magic line increased both the BW and the Friction. Both were
increased simply as a function of the extra weight of the tall heels.
Keeping a consistent heel height (and weight) avoided this extra
freight. Sort of like the article which Ken Sloane published in the
CAUT newsletter about 10 years ago. Found that a Steinway D action
was cleared of it's "truck-ulance" by switching to 17mm shanks even
though the jack-center/knuckle-core axis got seriously bent. What
looks the prettiest doesn't always play the best.
Action efficiency? Yes, you can describe it in terms of the measured
friction. But once you start measuring changes in friction brought on
by the various ways to change the way an action is "hung", you
quickly find that although fooling around with spreads and axes may
fine tune it for you, the "heavy lifting" (pun intended) is really up
to this business of tuning mass and leverage in an action.
Yes, I be as shameless in my promotion of the Stanwood Metrology as
"the other Bill" is about HT. I was convinced by David 10 years ago,
and have been moving caps and heels under his system for five. And
with that experience, Terry, I'd observe that if if your Boston
action feels weird despite such favorable BWs as you report), your
big clue will be in the FWs. If they are within bounds, then your
problem is more academic than real, and may in fact have more to do
with the sound coming back out at you.
IMNSHO.
Bill Ballard RPT
New Hampshire Chapter
".......true more in general than specifically"
...........Lenny Bruce, spoofing a radio discussion of the Hebrew
roots of Calypso music
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