impedance

[Ron Nossaman]

>
>Hi, Ron
>
>How about some system whereby the impedance could be "tuned" after the 
>piano was built? Some way of adding or subtracting weight from the bridge,
>and/or altering the stiffness of the ribs, without having to unstring the
>piano? Changing the impedance for local areas would seem to be desirable,
>to me.
>
>Susan
>

That can already be done, to some extent. Weights can be experimentally
screwed to the underside where (if) buttons are, without leaving any visible
damage. You could also clamp weights to ribs, if there was room around the
beams, and you had made a padded clamp that wouldn't hurt the rib. Then,
after you decided what worked best, the proper weights could be installed
permanently by screwing them into the bridge from underneath, between the
ribs. I don't see any problem at all with this sort of thing. It doesn't
look bad, and works quite well. Too much initial weight shouldn't be much of
an issue unless you like yard wide, Mason & Hamlin style bridges, and/or
bass bridge cantilevers the size of Cleveland, so there probably doesn't
need to be any way to lighten bridges after installation. Jim Coleman Sr.
and I were talking at Providence about the possibility of gluing stiffeners
to ribs in existing installations. Techs were installing springs between
posts and soundboards in verticals, and it did seem to help, but was looked
down upon by most (ick!). That sort of thing might very well be a
justifiable last ditch disaster control measure for a soundboard assembly
that wasn't really designed well in the first place, but I think the state
of the scientific art is finally to the point where we can anticipate enough
of the problems in the design phase, to not have to do that in a new
product. Making ribs more flexible just requires room around the beams to
get under there and shave them down, but not too much, or they won't support
the bearing load. This is sort of a last ditch thing too, but you can hide
the process after the fact with a little lacquer if you have to do it.
Again, I'd rather it weren't necessary if the problems can be minimized in
the design phase. I've been preaching to people for years to not design in
hardware. Do it on paper, in your head, or with a calculator or computer
first, where it's easier to mutate the ideas in process. Make  your
conceptual mistakes in the conceptual stages, and correct as much as you can
before you cut the first piece of material; before they cost you money and
blood. Just trying to follow my own advice for a change %-) 

Just by way of perspective; I still change things half way into the
fabrication process when I'm building jigs and tooling, but I had done it
fifteen different ways in my head and on paper before that. I may be
education resistant, but I'm not yet entirely education proof.

 Ron