Modal Analysis (was Negative bearing (long))

[Richard Brekne]

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Delwin D Fandrich wrote:

>
>
>      ----- Original Message -----
>      From: Richard Brekne
>      To: pianotech@ptg.org
>      Sent: December 04, 2001 12:20 PM
>      Subject: Re: Modal Analysis (was Negative
>      bearing (long))
>       Phil, Ron, and Del.
>
>      Here is a page from the text of Wograms article
>      that addresses directly I think Phils remarks,
>      and what I interpret as his assertion of the
>      predictability of modal analysis from the
>      unloaded to the loaded conditions. I would
>      highly recommend this whole article to anyone
>      interested or directly involved in work relating
>      to soundboard impedance issues. Even for someone
>      like me who just wants to gain better insights
>      such reading is valuable... so read away folks..
>
> Yes, Richard, I have the book and I've read the article.
> As I have said several time, my experience was some
> different.
>
> Del

Sorry if I seem er.... eager to help..... but it seemed like
you said you had very limited experience with Wograms
experiment and had little knowledge of his work and that you
based your tentative skepticism to modal analysis on just
one piano and that on the other hand you had learned quite a
bit from that one experiment about soundboards in general...
all that seemed just a little vague so I threw this out.


you reply to Phil kind of matter of factly about this again
when you say...


     "I can't see any advantage to this. Other than as
     a teaching aid to help
     understand how the soundboard works. It is only
     going to illustrate at what
     point the soundboard resonances come in and what
     their shapes are. Again,
     this is with an unloaded board. Everything is
     going to change once the
     strings go on and their up to pitch."

but you seem to be saying you have too little experience
with Wograms work and modal analysis (haveing done just one
yourself) to state this position as a fact...

You said....


     "Well, as I've said, I have limited experience
     with the technique. But that
     was on a new grand piano I had designed and built.
     So I was at least
     intimately familiar with the instrument and with
     what the designer intended
     to achieve with the design. I learned more about
     the design during the few
     days I was able to work with an engineer from B&K
     on the modal analysis
     project than I ever expected. It gave me insights
     into the functioning of
     the soundboard I doubt I'd have gotten any other
     way."

Now I dont mean to tick you off or anything Del... I am
really just trying to get straight what your experience base
is on this, and why you seem to feel so strongly that
Wograms standpoint on the relationship between unloaded and
loaded conditions is wrong.  Couldnt you describe a bit more
about this example you mention above... what you did, how
you measured both before and after and that kind of thing. I
would also be very interested in knowing what kind of things
you felt were valuable... you mention some insights into
soundboard functions... what particulars.

Could any of us learn any of these same things by carrying
out the sand experiment ?

--
Richard Brekne
RPT, N.P.T.F.
Bergen, Norway
mailto:rbrekne@broadpark.no


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