strike weight

[Stephen Birkett]

D. Stanwood wrote:

> Your arguments are well founded and I have given them due
> consideration in the past.  Based on what you outline here, it
> would be improper to use strike weight for calculations such as
> moment of inertia etc.
>
I'm really saying more than that...using statically determined strike
weights in *comparing* the dynamic behaviour of different actions may
give slightly distorted results. F.i. because the bass hammer is wide
(in the plane of its motion) it will dynamically not behave exactly
as if all the mass were concentrated at the strike line. Thus the
strike weights determined for the bass and treble hammers of the same
piano will not strictly be comparable...in terms of the `effective'
mass which hits the string. You did mention dynamic performance in
your post on the metrology.

> The strike weight measures make sense in that all modern pianos
> are constructed in a like form, having the hammer mounted roughly
> 5 1/16" out on the shank and the hammer bore distances are fairly
> consistant from make to make.  Anyone know of a piano with a 3"
> bore?  Relative to eachother, strike weight values may be used as
> an effective measure of how much weight is being thrown into the
> string, and our experience bears this out.
>

Experience is a good basis for ad hoc methods and what you say above
would seem to indicate that the static/dynamic difference is not
significant. To establish a metrology like this requires some
up-front analysis to verify that the techniques are valid (as you
have been doing of course)...I realize your requirements relate to
practical day-to-day work, but once this is published someone else
will point out what I've said...so I'm just suggesting that this
point should be checked now, so that it's insignificance is
verified quantitatively, and potential criticisms averted.

> The same could be said for the downweight and upweight measures.
> Crude but effective.  Pianos weren't invented by physicists.
> Things like what you speak of are very interesting but they don't
> have much to do with the day to day chores of the piano maker or
> technician, nor do the Pfeiffer books have much in the way of
> practical information.

As the piano developed it has really existed in a state of
experimentation almost continuously...enough instruments were built
by a maker that design features could be checked empirically. Now
that manufacturing precludes such experimentation for the most part
we should take advantage to the full of modern technology in
analysing design features. I understand that day-to-day requirements
are incompatible with complex analysis but that doesn't mean we
cannot take advantage of the knowledge gained. The stuff on
first/second moments, and also the Pfeiffer books, is really
nothing more than pretty elementary physics.

I don't find the Pfeiffer books very useful (and there are errors,
f.i. his treatment of energy efficiency) precisely because they are
too complex for `ordinary' purposes, but too simplistic to have any
connection with realism. For the project I referred to earlier, I
believe we can learn a lot about pianos using techniques from
simulation in robotics engineering...I don't mean to suggest these as
practical methods for the day-to-day technician. However I do believe
it will eventually be possible to completely simulate the dynamic
performance of a piano, from key to hammer and determine the acoustic
behaviour exactly...all with nice computer animation to show the
result. This is a *long* way off but the techniques are available
now.


Stephen Birkett (Fortepianos)
Authentic Reproductions of 18th and 19th Century Pianos
Waterloo, Ontario, Canada
tel: 519-885-2228
fax: 519-763-4686