Soundboard mass

[David Love]

Yes, I meant replacing but converting the original design.  

So would you say that the danger in adding the fish to reduce the area of
the SB in the treble would be extra stiffness but reduced mass?  And what
would constitute a light bridge?

David Love
davidlovepianos at comcast.net 
www.davidlovepianos.com

-----Original Message-----
From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf
Of Ron Nossaman
Sent: Monday, November 26, 2007 11:23 AM
To: Pianotech List
Subject: Re: Soundboard mass


> For those converting original pure compression boards to rib crowned and
> supported boards, how important would it be to consider the overall mass
of
> the total rib scale of the original design versus that of the new design
> versus, say, simply the deflection characteristics of the new rib scale.
> Further, is there a way to numerically describe the desirable
mass/stiffness
> ratio? 
> 
> David Love


Well, first, I'd say replacing compression crowned boards with 
new rib crowned and supported, rather than converting - etc.

One of the redesigns I did, I knocked all the old ribs off of 
the panel and weighed them together. Before assembling the new 
board, I weighed the new rib set. In spite of having three 
more ribs than the original, and in spite of the extra weight 
of the Titebond used in laminating them, the new set was 
lighter. But then they were also shorter, narrower, and some 
were deeper (some shallower) than the original.

What you're talking about is impedance, and the requirements 
of mass and stiffness differ with frequency. Build a 
thoroughly stiff treble into a board, and put as light a 
bridge as you can on it and listen to the result. You'll be 
reaching for mass loads immediately to "fix" it, where 
lightening a bass bridge won't produce a problem.
Ron N