impedance (was negative crown_

[Doug Richards]

Ron,

Next time I see you, I'm buying ...

doug (:-)
San Jose, CA

PS: Where in the world are you anyway?

> -----Original Message-----
> From:	Ron Nossaman [SMTP:nossaman@SOUTHWIND.NET]
> Sent:	Wednesday, December 30, 1998 1:53 PM
> To:	pianotech@ptg.org
> Subject:	RE: impedance (was negative crown_
> 
> At 07:38 AM 12/30/98 -0800, you wrote:
> >Frank,
> >Exactly my point!  Here I thought I was going to show how much I didn't
> >know.  In mechanical optimization of disk drives, we like to talk about
> >things we can measure and then change.  If you can't measure it, all the
> >beautiful words describing the concept are just that.  Why not switch
> gears
> >and talk of things you can measure and then optimize?  I'm a finite
> element
> >modeler so I do lots of computer simulations to show trends, but I always
> >have to talk in terms that  the lab guy can go out and test the structure
> >and corroborate my predictions.  He measures mechanical properties like
> >displacement, velocity and acceleration and can display them in terms of
> >real/imaginary or magnitude/phase as a transfer function.  These are the
> >tools we use to measure and describe vibrating mode shapes, resonant
> >frequencies, internal damping, transient shock response and so on.
> >
> 
> Doug,
> 
> I've put more than a few engineer types on the spot about this. Those that
> have even heard of mechanical impedance can't seem to come up with a way
> to
> compute it. "That's another flavor of engineer, I'm a -(insert
> specialty)-",
> is the universal disclaimer. There may be someone out there in engineering
> land who knows, but I haven't found him, or he's not admitting it.
> Meanwhile, an observed  general cause and effect relationship between
> measurable and predictable stiffness, mass, frequencies, tempered against
> an
> accumulated body of empirical evidence, and a healthy distrust of
> unverified
> "truths" is the best I'm able to do at present. I assume from tuning and
> servicing the current standard state of the piano manufacturers' art out
> there, that  the rest of the industry is in, at best, a similar position.
> Just like with disk drives, pianos are a complex cause and effect
> organization. It is only very recently that the mathematics of string
> scaling have been reasonably understood, much less how soundboards work.
> The
> informational components for understanding how soundboards work are, to a
> large degree, obtainable and predictable on a simplistic level. The
> concept
> of mechanical impedance is an attempt to put some of this data into a
> manageable format to get an idea of how it all fits together. Some day,
> someone will waltz in with a set of formulae that quantifies these
> interactions. Then we can all set around and wonder why in the world any
> given soundboard assembly was designed that way when any fool can see,
> right
> there on the spreadsheet chart, that it was done wrong. Someone has to
> build
> the tools to manipulate the concepts, and the tools themselves start as
> concepts, often crudely defined. Perhaps some enterprising finite modeler
> will come up something that does the job, and saves us all a lot of
> unnecessary work. He could make a few of us very happy. 
> 
>  Ron