Loud Blow, Soft Blow

[Stephen Birkett]

Sometime way back Jim DeRocher wrote:
> Several years ago I was amazed by ultra high speed photography of a hammer
> striking
> a bass string.  Two astounding revelations: (1) the hammer shank whips just
> like a
> good fly casting rod; (2) after hitting the bass string the hammer starts its
> return
> journey but the hammer itself is struck several times (three,  I recall) by
> the vibrating
> string before the hammer's return travel places it out of reach of the bass
> strings's excursion.  At the time I concluded, and I have seen or read
> nothing since to change
> this conclusion, that part of the energy imparted to the string was given
> back to the
> hammer by these return taps, thus weakening the tone, shortening the tone's
> duration,
> and altering the relative strengths of the harmonics.
>

The observation on the hammer shanks is amazing but quite
understandable when compliance and inertia are taken into account.
One of the objectives of my current research project is to analyse
and predict with a computer model precisely the sequence of events
that Jim describes from the high speed photography. The whiplash
effect is even more important on Viennese action fortepianos, and
one of the secrets to developing a fine tone, esp. in the treble, is
to use the thinnest possible hammer shanks...literally as thin as
matchsticks sometimes. I would be very interested to get a copy of
this film or anything else related...does anyone have any leads?

The second point Jim notes is also predicted by the better computer
models...energy is definitely lost to this effect, which is more
apparent in the bass since the heavier hammers take longer to
accelerate downward by the string. The result is that bass
hammer/string energy transfer is typically less efficient. The
accelerations involved in the hammer/string interaction are so large
that the effects of gravity are totally insignificant and can be
ignored in the analysis (this is presumably why the downstriking
action is possible).


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