What matters most?

[Richard Brekne]

David Love wrote:

> The question may seem absurd to the pianist who doesn't even know the names
> of the parts, but it's certainly not absurd if the piano isn't performing
> well.  As technicians, we need to be able to quantify cause and effect as
> much as possible if we are to have any chance of producing a predictable
> action, soundboard, or anything else for that matter.

I aggree, as I think we all do from this perspective.

>
> With respect to this question, I think what we are likely to find, and have
> found (thanks in large part to David Stanwood), is that a certain weight at
> the hammer end works best with certain action ratios.  Moreover, with
> respect to inertia, how that ratio is achieved will make a difference.  We
> can, for example, achieve a 5.6 action ratio with a combination of 16 mm
> knuckle mounting and .48 key ratio, say, or 17 mm knuckle mounting and .52
> key ratio.

Now this is interesting. And I again agree entirely. Yet it seems Stanwood
himself does not. He believes the particular combination whatever whippen and
hammershank ratios that make up the top actions overall ratio is of little, or
no consequence... or so he states in his latest writtings. According to this it
is the overall SWRatio that is of importance and not the individual factors that
comprise that product.


> Which one should we choose, given that we have a choice.  The
> answer, it seems, would lie in how heavy a hammer we wish to use.  A heavy
> hammer, from my experience benefits from a long knuckle mounting and a
> light hammer from a shorter mounting.  Though I can't quantify the inertial
> relationships (at this time), it would seem that inertia (as well as
> friction) would play a role.  The Overs piano that I saw in Reno, for
> example, had quite a heavy hammer on it.  Thirteen grams or so in the bass,
> if I recall correctly.  But it also had a knuckle mounting of 20 mm.  The
> overall ratio (I believe, Ron can correct me on this) was about 5.7.

I believe Ron Overs had David measure his action according to his vertical force
priority measurements. I dont remember what Ron mentioned was the result of
that, and the result of his own method, but perhaps he might share that with us.



> That
> piano certainly did not suffer from any inertia problems (it also had
> assist springs BTW).  That may not have been the case had the overall ratio
> been achieved with a shorter knuckle mounting and a lower key ratio.  Heavy
> hammers, contrary to other thoughts expressed, will not necessarily create
> inertia problems given the overall ratio and, moreover, the ratios of the
> component levers are a good match.

I wonder if you might expand a bit on how you see the hammers inertia being
changed by a change in knuckle diameter while compensating elsewhere to keep the
top action ratio and/or the overall ratio the same.

>
> At least that's my take on it.  So in answer to the original question:
> None of the above.  High inertia in the top action can feel just as bad as
> high inertia at the key.  I'll wait for Birkett's research to try and
> quantify that relationship further.  Fortunately, we don't usually have to
> make that choice.    In general, I'd say that the hammer weight and knuckle
> mounting position should move in the same direction.  Once that number can
> be quantified, then all that's left is to establish the key ratio that
> gives the desired overall ratio. That ratio (assuming no assist springs or
> magnets) will have to consider both the resultant front weight of the key,
> or key inertia, and regulation requirements.
>
> David Love
> davidlovepianos@earthlink.net
>

Thanks David. One of the angles on this I'd like some feedback on goes to the
question of just how important the keys inertia really is... and when does it
become important. At what (if any) point hammer inertia becomes so dominant that
any reduction in key inertia is not of any real benifit ? Overall leverage can
come into play, as well as the weights of the parts being leveraged. The lower
the overall ratio (regardless how its taken) the less hammer velocity for unit
key velocity.. That directly alters the inertia balance.... the lower the
ratio.. the more important key intertia becomes... and vice versa. This is one
of the reasons why I see Stanwoods claim that the overall ratio taken as a whole
is the only thing that is important.... it disregards that for same ratios
differeing inertia relationships can exist for the hammer and keystick.


--
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