Changing upright bridge location & affects

[Michael Spalding]

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Dale,

I have just finished a rebuild of a 5'3" Hardman grand in which I replaced a cantilevered bass bridge with a solid bridge attached directly to the soundboard.  In my case, the only practical way to repair soundboard cracks and rib separations was to remove the bridge - then, since it seemed logical to me that all that damage was caused primarily by the twisting load from the cantilever, I decided to make a solid replacement.  Bridge location was somewhere in between the old apron and old bridge, as dictated by the opening in the plate, rotating it slightly counter-clockwise to lengthen low-bass back-scale and keep the bridge from being exactly parallel with soundboard grain.  Re-scaled by Arledge (compromising Inharmonicity slightly to achieved tuned longitudinal mode).  Tonal results:  clean, clear, even.  Smooth tenor break.  Somewhat shallow or inelastic tone in bass, but it is only 5'3".  note 1 length decreased from 46.6 to 46.2, and note 26 length increased from 36.1 to 36.5.

hope this helps

Mike


----- Original Message ----- 
From: Erwinspiano@aol.com 
To: pianotech@ptg.org 
Sent: Saturday, November 22, 2003 9:50 PM
Subject: Chaging upright bridge location & affects


   List
    I wanted to pick your brains so here it is. 
    Last week I took in a large 54' 1903 Schaff Bros. upright for restoration. It has a beautiful Victorian style case an intact & legitimate soundboard. Among the usual things it will also get a complete set of bridge caps. The bass bridge has the half moon shaped bridge mounted on the usual apron & the bridge body itself has a vertical crack thru to the apron that was repaired by installing several screws. 
    Since I need to do extensive repairs anyway I'm considering building a solid bridge & attaching it to the board where the apron is currently joined. The current string lengths on note 1 is a very long 51& 1/2 "& note 28 is 41 & 1/2". If I relocate the bridge It will be shortening those strings by 2&1/2" on note 1. & 3 & 1/2" on note 28. The new length will be  49'& 38 & 1/2" respectively. Still long strings.  Because of the half moon shape the longer strings will become even sorter especially if I use a straight bridge which, would be simpler. The middle& longer strings would be shorten by as much as 5."
   I'm looking for feedback from others who have done this or have an idea about it. A prime consideration for me is, will this improve or inhibit damping? How will it improve the sound? From what others have said just attaching it to directly to the board will improve mechanical efficiency. No argument there,
    In most uprights the dampers best location would be where the hammers hit the strings but obviously they can't be there. Also I don't want to end up with the damper on some nodal point that creates some harmonic that I can't resolve. In fact perhaps this is why the strings on most uprights are so long perhaps to mitigate that effect. I don't know. Will shortening the string push the optimal damping point even further up the string towards the tuning pins? That to me would be bad.
  Interestingly and for sake of comparison a Mason A Bass note 1 & 26 is approx. 49" & 36" Which is close to where a modified length will be on the upright. Also the tenor string lengths are fairly comparable in both pianos.
    Any insights will be of course be appreciated & as always stimulating & helpful.
   Thanks in advance--Dale Erwin
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