Aftertouch, WAS Re: Action Geometry Consistency

[Richard Brekne]

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Im going to take a different take on this whole aftertouch subject, as it seems
we get so hung up on looking at it from a blow perspective, or a dip
perspective that we forget what the whippens roll in all this is.

Ideally, if the whippen is perfectly set, then aftertouch is nothing more or
less then the amount of whippen travel (felt at the key) beyond that neccessary
to get the jack top out from underneath the knuckle after letoff. The <<
perfect set >> for the whippen has :

     1. Consistant jack travel... which in this perspective means that
     jack at rest position is the same for every whippen.
     2. Let off is set to a specific value, consistancy being very high
     priority. I like 1.5 mm myself.
     3. Jack top and repetition lever both supporting the knuckle. This
     means the repetition spring has to have enough strength to support
     the hammershank on its own, as well as meaning the height of the
     repetition lever is the same as the jack top.... plus the thickness
     of the hair from a rats eyebrow.  Just enough to let the jack slip
     (with a tad bit of coaxing) back under the knuckle.
     4. The drop screw and the letoff button are engaged at exactly the
     same instant. This is affected by both the 1st and 3rd items above,
     so they have to be dead on consistant. If not, this simultaneous
     engagement of drop and letoff will contain those inconsistancies and
     reflect them further in the form of aftertouch problems.


The combination of blow and keydip is what decides how much this whippen moves.
The whippen, configured as above, does not need to move any more then is
necessary to get the jack barely clear of the knuckle. Drop is quite minimal,
as the jack starts moving forward and upward independantly from the repetition
lever at exactly the same time. The jack tops motion is then a combination of
the arc of its own axis, and the arc of the lower arm of the whippen for that
last little bit of whippen travel, which isnt going to push the knuckle much
above the drop position.

So, what I do is to first make sure my spread is good, which also gives me my
blow. (This has to be compatable with an acceptable key dip moving the above
configured whippen just enough to get the jack clear of the knuckle.). I set
blow as even as I can get it, but I make sure of a clean whippen line. If the
resulting hammer line is too bad.. then I decide whether or not to correct the
bore on some of the worst hammers, file them even, or fudge a bit with the
whippen height, tho I dont allow for much of the latter. Then I configure the
whippen, and then I set key dip.

I usually do at least two passes to refine the adjustments.  Drop is minimal
and very consistant, and the "feel" of going through lettoff and drop is as
identical from key to key as it can get. Whatever errrors there are in the
action I put in to key dip. Unless you have a really inconsistant ratio, the
amount of variance does not seem worth mentioning, and even then it seems that
the consistancy of feel through letoff/drop is more important to the pianist.

So I  agree with Bill when he says..."The dip can be whatever it and the blow
and LO have worked out together."

Ok... so who's up next  ?  :)



Cheers

RicB

Bill Ballard wrote:

--
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


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