Negative crown

[Doug Richards]

Del,

I agree completely.  It's just that impedance is not the property I'm used
to using.  On mechanical structures in the lab I measure the force and
frequency response (transfer function) when understanding a mode shape.  I
can see the time and frequency domain force input, the resulting
acceleration of the measurement point and the internal damping of the
structure.  After taking multiple measurements, I can visualize the
structure response at any frequency in question with modal analysis software
(or just the plots for a simple structure).  I have never wanted to look at
the impedance that I know of but you can teach me..

doug

> -----Original Message-----
> From:	Delwin D Fandrich [SMTP:pianobuilders@olynet.com]
> Sent:	Tuesday, December 29, 1998 6:54 PM
> To:	pianotech@ptg.org
> Subject:	Re: Negative crown
> 
> 
> 
> Doug Richards wrote:
> 
> > Ron,
> > Very well put.  I think we are talking the same language.  The only
> > difference I have is my dislike for the word "impedance".  In my line of
> > work, the only people that talk of impedance is them electrical guys
> (you
> > know, the ones that need scopes to see what they are doing).  I am much
> more
> > comfortable talking about mode shapes, resonant frequencies, dynamic
> > coupling and the like and leave the impedance to the EE's.
> >
> > The reason I replied to your thread in the first place is reflecting on
> > previous threads about Killer Octaves.  Seems like there should be
> someone
> > that optimized the impedance so that the Killer Octaves died.  Maybe we
> > haven't figured out the best way to kill it yet...  (or more likely,
> another
> > manufacturing problem or reliability issue comes up again).
> >
> > Anyway,  thanks for the reply.  And YES, we are having fun!
> > doug
> 
> ---------------------------------------------------------------
> 
> Ah, but Doug, the idea of mechanical impedance, or wave impedance, is very
> important if one is to understand the function of a vibrating body such as
> the
> piano soundboard.  It is a function of the square root of the inertia
> times the
> springiness of the vibrating system.  For a simple and piano specific
> explanation of mechanical impedance, might I suggest the chapter on Sound
> Production in Pianos in Arthur H Benade's book, "Fundamentals of Musical
> Acoustics."
> 
> Regards,
> 
> Del