Bridge design

[Ron Overs]

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Hi all,

Dale wrote;

>. . . Oddly enough I just purchased 2 Mason As . One from 1929 and 
>the other 1931. The 1929 has the usual long tenor bridge and the 
>other has a modified tenor bridge. The bridge makes an abrupt swing 
>towards the staight /bass side of the case. This shortens up the 
>speaking length bout 3 or 4 inches and on it are of course 5 wrapped 
>bi-chord unisons. The plate area at the agraffes is also shortened 
>appox. an inch.
>   I found this to have a very good bass tenor break and a step in 
>the right direction with this model considering the break with plain 
>wire has been changed i different wire size configurations over 
>time. And with not much success. To bad that Mason& Hamlin didn't 
>stick with it. No doubt more costly .SO WHAT. Any rebuilder could 
>easily duplicate this modification except the agraffe change.

While it is possible, for pianos which have bichords on the long 
bridge without employing a transition, to achieve a good tonal 
transition from the tenor to the bass bridge, the transition from 
plain trichords to covered bichords will always be a mess. There is 
just no way of scaling a way around the problem without having a 
reduction in speaking length in the adjacent bichord note (this can 
be proven with both the tuning lever and the spread sheet).

Del wrote;

>A better solution would be to straighten out the scaling in that 
>area and use an extension on the end of the tenor bridge to stiffen 
>up the end of the bridge

Indeed Del, we use an extension at the end of the long bridge to 
achieve the impedance we're after. A ring bridge might well stiffen 
the low end of the treble bridge, but it will also stiffen the low 
end of the bass bridge, which is not exactly what we want at A#1.

>  -- even better, design in a transition bridge -- and/or redesign 
>the ribbing, and leave out the gaps.

Agreed. Of course, the transition bridge is a really sensible work 
around for a piano which has bass/treble break which is lower than 
desirable, for the particular length of piano.

Interestingly, something I have noticed about transition bridges is 
that they also need an extension running out from their treble end, 
to increase the impedance. This extension would therefore run further 
out towards the center of the board. I am thinking now that it should 
be long enough to run over another sound board rib. Of course, none 
of this stuff would be necessary if the cross was in the appropriate 
place to start with. After a hundred years we are still stuck with a 
multitude of small and mid sized grands with the cross scaled too far 
down, just to make them look like their bigger brethren.
Its time the marketing department was gotten out of the scaling room, 
'cause all we end of with are little grands which are pretty, but 
pretty damn useless.

Ron O.
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OVERS PIANOS - SYDNEY
Grand Piano Manufacturers

Web: http://overspianos.com.au
mailto:info@overspianos.com.au
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