impedance

[Susan Kline]

At 11:25 PM 1/3/99 -0600, you wrote:
>>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
>>
>
>Hi Susan,
>
>Sure it could. With vertical hitch pins, the factory/tech can both set the
>bearing precisely where he/she/they want(s) it in all areas of the piano,
>and can still change it later, at any point, if the need is perceived
>without having to add the weight, complexity, and less than solid adjustable
>bridge. An adjustable soundboard spring system is certainly possible, but it
>would not only be more expensive and heavy, there wouldn't be one tech in
>fifty who would take the time, or care to learn how it worked and how, and
>when, and when NOT, to adjust it, or the bridge or vertical hitch pins for
>that matter. Sounds a smidge cynical? That's some of that resisted education
>that was finally pounded into me through endless repetition. Personally, I
>think a well designed system can be stable and dependable, with a reasonably
>long service life, without having to do a lot of after the fact tinkering
>with it. I'm a real fan of low maintenance simplicity. The trick seems to be
>gathering enough of the right information to fill out the picture with
>understandable cause and effect relationships instead of just putting band
>aids on the boo-boos. I want to avoid the problems altogether if I can, but
>that's just me, and there still a lot of holes in the picture.
>
>Best, 
> Ron 

Yes, point taken, at least as far as production models go. But what a study
tool it could make! See what _actually happens_ when you change this or that. 

For instance, if you move a soundpost on a violin or a cello a tiny
fraction of an inch, the whole character of the tone and responsiveness can
change. What if someone had decided that they could _design_ it to be the
right place, so they made it so it couldn't be moved? It seems to me that
"practicality" in piano building has been doing similar things for years.
That is, the fixed design has meant that any experimentation with piano
parameters can only be achieved with weeks or months of effort and great
expense. 

What would happen, for instance, if instead of one long treble bridge all
screwed and glued in place you had 8 or 10 little ones of a few notes each,
which were just pressure fit, and held on by string pressure, like a
violin's? You could move them around and find the RIGHT place for them, or
see how the character of the tone changed for different places. This might
enable you to see how much of an instrument's tone was inherent in the
board, rim, and plate, and how much was an artifact of bridge placement and
height. It would also be fun if a way could be devised to have movable ribs
with adjustable stiffness, without having to unstring or lower the string
tension. By putting pressure on the ribs from underneath instead of
counting on gluing and clamping to make the board conform, they might be
made adjustable and movable ... of course one would have to allow for the
coupling of whatever was pressing on them.

Just gathering wool again ...

Susan

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