[CAUT] Bridge design/Pure sound wire

[Ron Nossaman]

> First of all, the piano I'm trying it on is my own Vose and Sons
> ($500.00) so I can experiment, somewhat. Juan Mas Cabre is sketching a
> new bridge design, and with Vince's help I'll make an entirely new
> bridge. The grain, etc. will be somewhat like a Steinway, but with the
> type of bridge cap you taught in your class.
> 
> Here are some of the suggestions Juan gave me:
> 
> Concerning the "Pure Sound Bridge" on the Vose&Sons:
> 1. The treble part needs to be shifted towards the capo bar by a number
> of millimeters( I can calculate). It could also be made a little
> narrower, to lower bridge mass a bit.

In my experience, lower mass is about the last thing you need in the 
treble. Try to resist.

Are you calculating a new semi-log scale throughout? These changes 
need to be looked at on a scaling program or spreadsheet, and these 
scaling decisions and the room you have to work with in the piano 
will determine the bridge shape.


> 2. The cross-over section with the treble frame bar needs to be shaped
> much like on a Steinway-M bridge: small S-shape, taperad down at the
> bottom to reduce stiffening the sound board and at the same time smooth
> out the S - bend. The "S" shape will dileberately be shaped smaller than
> needed for speaking length correction, using the top surface to do the
> rest of the sp.length compensation by arranging the pins more forward or
> backward, making speaking lengths in a nice and regular row this way.
> 3. The lowest two or three notes of the unwound section would benefit
> largely from a bit more speaking length. Leaving the contact area the
> same as in the original, the top 2/3 of the hight of the wood could be
> shaped outwards by about an inch. Hopefully the plate edge is not in the
> way. In any case this bottom part of the long bridge must get little
> "feet" to stand on, stepping over the rib(s) so as not to stiffen this
> critical area unnecessarily.

More often than not, I find the low tenor too flexible already, and 
the speaking lengths too short to get the wire break% up to workable 
levels. The S&S M is a pretty good example of how not to do it. The 
bass/tenor break should be at around #32 in that piano. That's why I 
like transition bridges there. I can shorten the speaking lengths 
and put in wrapped bichords, eliminating the hockey stick and 
getting tension and break% up in the low tenor. I can also extend 
the transition bridge closer to the side of the case, adding needed 
stiffness without losing what flexibility I have under the low bass. 
This is assuming a rib scale designed to accommodate the bridge 
configuration and string scale.


>  We need drawings, of course, but maybe this gives you an idea in which
> direction I am thinking.
> Maybe brass bridge pins for the front row, facing the speaking length,
> are an option, or maybe just on the three top treble octaves, for more
> tuning stability. The polished stainless steel wire slides perfectly
> against brass. If there is very little room for slightly thicker pins,
> an epoxy treatment of the top of the bridge can work wonders! These
> brass pins do not need to be much thicker than steel ones, since the
> string tensions in this area are relatively low.

I don't understand how the friction coefficient of brass pins would 
improve tuning stability.


> This is where I'm starting. I've made bass bridges (eliminating
> cantelevers) but never the long bridge. If it is simply a matter of
> making the same design as is already on the Vose and Sons I can do that,
> but I'm betting there is much improvement to be done.

I'm sure there is much improvement possible, most of which would 
come from a new soundboard and rib scale.


> See what you've started?? Now I've got the bug to stretch much more than
> I've ever done! Thanks, BTW.
> 
> Jim

Bear in mind, I've not had experience with Pure Sound wire, nor put 
new bridge designs onto existing soundboards, so there might very 
well be surprises. I assume you checked for bearing and crown in all 
reachable areas before tear down, and otherwise ascertained that 
this was a reasonably functional soundboard, so all this work won't 
be wasted. Or is the board being replaced as well? The Vose and Sons 
pianos I've seen had very peculiar ribbing and (as I recall) panel 
grain orientation. There's always interesting trouble to get into, 
and the education never ends.

Ron N