Killer Octave Question

[gordon stelter]

Um, didn't Mason and Hamlin once supply dealers with a
little demonstation gadget, in which a "rib" lay on a
base between two rigids ends positiouned at exactly
the "rib's" length. The insertion of a mere business
card between one end and its stop then caused  a
marked rise in the rib's center.
     Thump

--- A440A@aol.com wrote:
> Ron writes: 
> << Soundboard crown still isn't supported like a
> buttressed arch, Ed, and rim 
> or belly rail spreading the few thousandth's
> difference between the length 
> dimension measured straight from rib end to rib end,
> and that measured from 
> rib end to rib end over the crown won't make the
> crown go flat. It just 
> won't.<< 
> 
>   I know that someone has done the math on this. 
> How much "spread" is 
> required of a rib that is 20 inches long, curved on
> a radius of say 40' to 
> allow the center to drop .020"???  It has been too
> long since I dragged my 
> kids through high school geometry to remember arc
> and such, but I know 
> somebody out there has the answer at hand. 
> 
> >>Flexibility in the belly rail and rim will
> certainly damp the 
> soundboard and affect tone production adversely, but
> the crown is formed 
> and supported by rib and panel, independent of the
> rim.  >>
> 
>    There is evidence for debate on the arch theory.
> The observed change in 
> the Mason & Hamilin centripedal resonator when the
> strings are removed.  In 
> every case I have seen, (more than several),
> destringing a Mason changes the 
> tension on the bars, ( judged by rattles that appear
> when destrung).  
>    Perhaps the strongest indication I know of that
> the arched board attempts 
> to spread the case is the Chickering grands with the
> inner rim.  All of these 
> pianos,(I have had 4 of them), when destrung, show
> the inner rim to come 
> inwards.  A wedge that is very lightly placed
> between the inner and outer rim 
> before stringing will be extremely tight when the
> strings are pulled up to 
> pitch and the screws that pass from inner to outer
> around the perimeter will 
> also be looser.  There is definitely outward
> movement of the relatively 
> flexible inner rim under downbearing pressure.  If
> the board simply presses 
> downward on the shelf, this particular construction,
> with its cantilevered  
> support, would bend inwards, no?  These Chickerings
> also have really nice 
> sound with virtually no bearing, even though without
> any strings on them, 
> there is a boatload of bearing  They simply flatten
> out and I have, in the 
> past, attempted to add bearing by lowering
> nosebolts,but the board just keeps 
> on flattening out as I do.  
>     The unsupported span of the belly rail on grands
> often has a slight curve 
> outwards between the horn and their attachment to
> the treble case side.  I 
> don't think this was built into the pianos
> originally, so  what other force 
> but soundboard spread would do this?  
> Ed Foote RPT 
> www.uk-piano.org/edfoote/
> www.uk-piano.org/edfoote/well_tempered_piano.html
>  
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