[CAUT] Soundboard mass

[David Love]

Since my general protocol on rebuilds using original boards (Steinways
anyway) is to recap the capo section which often involves increasing the
bridge height, I have generally noticed (though very unscientifically) some
gain.  It wasn't clear to me whether that was simply due to rescaling that
section (I usually increase the tensions somewhat as they are often a bit
low--especially on the smaller grands), improved terminations, or, as we are
discussing, an increase in stiffness, as you have pointed out.  Since adding
stiffness is the usual goal on older soundboard killer octaves, what, if
any, would be a reason to not do this generally?  What sort of increase in
bridge height would be needed to effect a change in stiffness in that
section and what do you think might be the point of diminishing returns and
what would those be?  Something to ponder while gnawing on that turkey leg.
Or am I just full of stuffing?

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: Wednesday, November 21, 2007 4:51 PM
To: College and University Technicians
Cc: 'Pianotech List'
Subject: Re: [CAUT] Soundboard mass





> Anyway, I'm wondering if others have done similar things with similar
> outcomes or found that bridges below a certain height simply don't have
> enough mass without some help.  Further, with a certain minimum bridge
> height does mass loading become unnecessary?  

I think it's stiffness, rather than mass that makes the most 
difference in the taller treble bridge. Addition of mass 
doesn't typically do much good for the classic killer octave, 
but mass loading a treble that is too stiff and screaming wild 
with short sustain helps considerably. It's a resonant 
frequency thing. 
http://www.kettering.edu/~drussell/Demos/SHO/mass-force.html


>I've often wondered if the
> early Steinways with bridges under 30 mm in the treble (and sometimes well
> under) don't compromise those areas by virtue of inadequate height and
> therefore both mass and stiffness to begin with.  

I'd say so. That and the compression crowned boards.


> Moreover, is there what one would consider an ideal bridge height?

You can get away with a shorter bridge with more ribs, where 
fewer ribs need the added stiffness of a taller bridge. One of 
those "it depends" sort of things - again. Assembly stiffness, 
mass, and frequency response requirements are the thing, and 
variations on proportion among the assembly's parts can 
average out similarly in practice. The rules are different, 
naturally, in different parts of the scale.


> BTW Ronsen Bacon hammers with plenty of power (after a more refined filing
> in the treble) and warmth!  No lacquer, no plastic!

MMMMMMMMMMMMMMMmmmmmmmmmmmm, yea.
Ron N