Modal Analysis (was Negative bearing (long))

[Richard Brekne]

Phil, read Wograms article from the 5 lectures and see what you get from it. I am going to take another look throught this weekend, but it seems to me that he is saying that you can do just what you point out below. Course I could be mis-reading but it seems like he is saying that changes, and significant ones between the loaded and unloaded situation are apparent... but are predictable.

On the side and off a bit into the mists of Avalon if I may..... I seem to remember hearing somebody throwing one of those Steinway stories at me years ago about throwing sand on an unloaded soundboard and putting a set of frequencies on the panel to see what pattern the sand went to... and then trimming, sanding, beveling...whathaveyou the panel appropriatly to achieve a certain pattern they had found led to what they considered the desired result... does anybody know anything about this... whether or not its just another one of those myths... It sounds essentially like a kind of modal analysis technique..

Anyways Phil... read Wograms article... its available on line ... if you need the address just give me a wink... and let me know what you think.

RicB

Phillip L Ford wrote:

> On Mon, 3 Dec 2001 23:36:00
>  Delwin D Fandrich wrote:
> >
> >OK. My previous answer was incomplete. But you're taking what I said out of context. What I said was, "One of the problems I have with most of the testing I have seen on the piano soundboard is that it was done on an unloaded board and is, therefore, largely meaningless." This is some different than you are implying above. It is my opinion that tests of this type are basically meaningless unless they are done on soundboards installed in a real world piano, strung and loaded. Remember, we're not just trying to figure out the specific characteristics of the soundboard alone, but the entire, interactive system. No where do I preclude the possibility of obtain useable results from pianos that are strung and at pitch.
> >
> >  Del
> >
> I'd like to put in my two cents worth if I may.  In my opinion what we should be hoping for from
> modal analysis is a way of relating the behavior of the unloaded (and perhaps even uninstalled)
> soundboard to its final behavior in the piano with the strings on it.  Understanding the built up
> configuration is only part of the picture.  Until we can relate this back to design or construction
> parameters for the piano itself then this information is interesting, but essentially useless.  But
> if you can test and analyse  individual components and determine a way of relating their
> behavior to the behavior of the whole then you can start to make changes to the components
> that will affect performance of the whole.  Violin makers have been doing this for centuries.
> Old makers spent years learning to feel top and back flexibilities that were necessary for the
> completed violin to function well.  In our own time these flexibilities have been quantified
> through modal analysis and practical methods useful to the modern builder have been
> developed to aid in the process so that he or she doesn't have to rely on years of 'getting the
> right feel'.  Other parameters such as air modes, neck stiffness, etc. have also been quantified
> and related to the performance of the completed instrument.  These are very useful tools
> available to the modern violin maker.  The piano maker has no such tools.  Modal analysis is
> one of the things holding some promise to provide us with these tools.  It would be a huge
> research project but, as Del pointed out, a company which depends on piano sales for their
> large income should be spending money on R & D and this is just the sort of thing they ought
> to be spending it on.
>
> Phil
>
> ---
> Phillip Ford
> Piano Service & Restoration
> 1777 Yosemite Ave - 215
> San Francisco, CA  94124




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