impedance

[Susan Kline]

Dear Ron,

Actually, I had something a little different in mind. I was thinking of
designing in a system for fine-tuning impedance on purpose, as the piano
changed with age. That is, a system which didn't have to be hidden or
covered up, but was just designed in from the first, like tuning pins. I
could imagine, for instance, something built into a bridge which would
enable one to change its height. Double bass players have bridges like
that, since their instruments change so much with the season. 

Suppose, for instance, since people say those crazy automotive springs
actually worked sometimes, that a large beam went under the middle of each
rib, and an adjustable spring were mounted there. Each rib's amount of
support for the board could be individually tuned, depending on how the
instrument felt in a particular climate or at a particular age ... okay,
silly, but I just wondered whether it could be done ...

Susan


At 07:54 PM 1/3/99 -0600, Ron wrote and quoted:
>
>>
>>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 
>
>
>

Susan Kline
P.O. Box 1651
Philomath, OR 97370
skline@proaxis.com