[CAUT] touch & tone

[Ric Brekne]

Interesting stuff as usual Stephen.  I for one am really glad for your 
approach to all this, and that you take the time to share this with us 
through various PTG channels. If there was some kind of honorary 
membership for guys like yourself... I am very sure I would nominate you  !!

Cheers and thanks for your many contributions
RicB
....................

Some comments that appeared on caut list about the Askenvelt/Galembo
article in the August PT Journal:
 >I wouldn't read too much into the results of the shank vibration
 >study because the vibrations were generated in an experimental setup.

I think you mean "because the results were generated in an
experimental setup that was not representative of the conditions
pertaining in a real piano action in use". The hammers were clamped
and driven by oscillators acting at the knuckle to determine the
resonant frequencies.

 >As far as I know the different modes have not been isolated in real
 >piano playing.  I also don't believe modes have been related to tone
 >production.  The systems we're dealing with are incredibly complex,
 >and generating meaningful data is unbelievably difficult.  Stay
 >tuned--there is more coming in future articles.

As for the first point, we have observed hammer shank vibration modes
in high-speed imaging of actions played under normal conditions. They
are not easily seen on the upward moving hammer, because the speed is
fast compared with the natural frequency of the shank vibration, so
you only see a small protion of a cycle going up. Also the amplitude
is rather small (ca 1-2mm effect on the hammer head). On the downward
journey, as well as during contact, you can see a distinct
oscillation under certain kinds of touch. Post-processing of the
videos is effective at extracting the data on these modes of
vibration.

On the second point, that has yet to be determined. In fact, we don't
really have a good understanding of the hammer-string interaction and
how even hammer design affects it, so the effect of shank flexibility
on tone would fall under that study. We are starting to look at the
relationship between hammer properties (including shank) and the
precursors of string vibration (those travelling pulses). This is
actually a funded project that is just starting this week with a new
PhD student.

One final comment. The effect of hammershank vibration can be
observed by the effect it has on causing hammer head to move (the
shank/head glue joint is effectively rigid). This can change the
contact footprint (scuffing). A 4ms contact, for instance,
corresponds to a 250Hz cycle, so the shank vibration frequencies are
definitely in the range where about 1 cycle or more occurs during
contact with the string. If the amplitude is large enough and
friction with the hammerhead and string is low enough you can
typically expect motion in the order of 1mm during contact for a loud
bow with a flexing hammershank. This scuffing we have observed with
high speed imaging. We have also confirmed the frequencies with
strain gages mounted on the top of the shank. All during regular
playing of the key, not artificially clamped and driven hammershanks.

(I've included this on the pianotech main list too, since it is a
fairly general subject that may interest people not on caut as well.)

Stephen