Yamaha Jumping Jacks

[Ron Nossaman]

> Follow-up to my previous post, (below). Please bear with me.
> 
> I had the opportunity to do preps on two new out-of-the-box Yamaha uprights
> today, so I did a little experimenting with this double-strike phenomena.
> What I think I may have discovered is that it just may be operator error on
> us, (or is that we), techs that is causing this. 

It is.


> What I found was that when pressing the key down slowly I was sort of
> unconsciously pausing, just for an extremely minor moment, at the exact
> instance that the jack just starts to move out from under the butt. At that
> exact moment, when you are moving slowly, there is a very slight, but
> noticeable, increase in resistance as the jack starts to rub against the
> butt in it's move to escape. What I found myself doing was reacting to that
> subtle increase in resistance and almost unconsciously changing the motion
> of my finger pushing down on the key. In other words, I believe I was
> perhaps actually introducing the phenomena into the system myself. 
> 
> What I observed happening was that since the hammer was already in motion,
> the slight pause that I was introducing allowed the hammer to continue to
> move, leaving the jack and subsequently striking the string and then
> bouncing back, at which point I would continue pressing the key allowing the
> action to complete it cycle and giving me that second strike.

The length ratio between jack and the toe is high in these actions. 
A small amount of upward wippen travel moves the jack a long way. 
This also means that any slight resistance at the jack top will be 
felt greatly amplified at the jack toe, and felt in the key. People 
inexperienced with these actions tend to stop pushing when they feel 
this resistance, the jack doesn't escape, and the hammer double 
strikes. The "cure" is for the pianist to learn to run the 
instrument, and push through this resistance into actual letoff and 
to bottom the stroke on the front rail punching. Lacking that 
(people are relentless), the only thing I've found that works is to 
cripple the action by  setting letoff in the 13mm range to get that 
jack resistance too early in the stroke for the operator to screw it 
up. Later, when they start complaining about feel and repetition and 
are ready, the letoff can go back where it belongs and they'll 
(usually) adapt - or they just never complain. Incidentally, rather 
than spend an hour cranking letoff buttons down, it's easy enough to 
just bend the brackets Q&D in a couple of minutes. Reversing the 
"fix" later is almost as quick, with some quick ballpark bending and 
a touch up pass turning buttons.


> My guess is that this may turn out to be a new piano only effect. Once the
> piano has been played for a while and "broken in", and the butt leather
> smoothes out a little this may be impossible to reproduce at all. And as
> long as I'm guessing here, I don't think anyone but a tech could even MAKE
> it happen. Certainly not the person at home just playing the piano under
> "normal" circumstances. 

This also happens in used pianos with new owners who had been 
playing old worn out Gulbransen spinets and such. It's mostly 
operator induced.


> I find the combination of piano action physics and our human reactions to
> what we see and feel as a result of those physics all very interesting. I'll
> shut up now.
> 
> -- Geoff Sykes


Frustrating too, as the physics are largely misunderstood or 
ignored, and we attempt to fix something from second hand subjective 
impression. There are still plenty of times when an explanation of 
the problem doesn't suffice and I have to cripple the action with 
the extreme letoff.

Ron N