Mass versus Stiffness was RE: false beats from ?? -...

[Ric Brekne]

Hi David

Since no one else jumped on this I'll offer a couple comments.  As to 
target mass/stiffness ratio I think that rather depends on what it is 
you are trying to do, what kind of sound in the different registers and 
sound balance in general you are after, what kind of structural strength 
you feel is needed, and how you go about achieving these to begin with.  
As for mass / stiffness ratio in different parts of the piano.  Thats 
been tossed around here quite a bit over the years, especially comparing 
bass to treble and I am sure you will find all kinds of references in 
the achives. This same goes to disscussions about the treble fish and 
cuttoff-bar, tho perhaps to a lesser degree as to how directly they 
require a rethinking of any  mass/stiffness ratio concerns. That said I 
believe the main purpose of a cutoff bar is simply to reduce the area of 
the soundboard so as to be able to provide stronger support for the 
assembly and in some cases to purposefuly manipulate some of the 
soundboards impedance characteristics.  Rib width and height 
relationship is very well, tho briefly, described in the five lectures. 
In particular interested readers should check out 
http://www.speech.kth.se/music/5_lectures/wogram/ribbing.html#height 
which deals directly with your specific question.

I was interested to read Ron O's statement that mass/stiffness ratio 
contributed to a "propensity for falseness".  If he was talking about 
the same kind of false beats that the previous discussion was based 
on... then that strikes me as rather significant with regard to 
indentifying a root cause for those same. Certainly if changing the 
mass/stiffness ratio alone is a totally isolated issue from loose bridge 
pins.  It would be interesting to gather some relavant data comparing 
instruments with lots of false beating with instruments that have 
little.  Grin... one could start with Petrofs !! False beat city, yet an 
overall nice open sound.

Cheers
RicB




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1.  Is there a target mass/stiffness ratio and how is it described
numerically?
2.  How does it differ in different parts of the piano?    
3.  Does adding a cut-off bar and/or treble fish reduce the mass by virtue
of a decrease in the area of the board such that some compensation is always
required to rebalance that ratio?
4.  Does changing the rib width to height relationship influence mass
stiffness ratio?

For starters anyway.  

David Love
davidlovepianos@comcast.net