Spreadsheet info / Jason Kanter

[Frank Emerson]

As I understand the original question of this thread, it might be
paraphrased as:  Why not allow the wire gages to deviate from the expected
progression from larger  to smaller sizes, from bass to treble?  I cannot
imagine a circumstance where this would be advantageous or useful, except
in the case pointed out by Tom Cole, at the tenor-treble break, or with any
break(s) that occur along the long (treble) bridge.  I know some piano
designers who would calculate the string lengths as though the piano were
to have 89 or 90 notes, eliminating the note(s) that would fall "under" the
plate bars intersecting the treble bridge.  Others would compromise this
approach, and make the deviation from the logarithmic progression something
less that a semitone deviation across the break.  In any case, their intent
is to eliminate or reduce the dogleg across the break(s).  This is
especially problematic with vertically laminated bridges, since there is a
limit to how sharply the bridge can be bent without introducing serious
manufacturing problems.  In fact, there are some piano scales designed with
an intentional deviation of the wire gage progression for this very reason,
but only at section breaks.

Starting with a blank piece of paper, designing a new piano, I prefer to
calculate the string lengths with a pure logarithmic progression, and deal
with the dogleg of the bridge in other ways.  By making the distance from
the front bridge pins to the back bridge pins longer on one side of the
break, and shorter on the other, the dogleg in the bridge can be reduced. 
The side bearing angle can be maintained, even thought the distance, front
to back, is varied.  The bridge can be undercut, to further reduce the
dogleg of the bridge, at least with respect to the gluing surface between
the bridge and the soundboard.

When it comes to restringing a piano, when the treble bridge is not being
replaced, recapped, or repinned, I would not hesitate to reverse the wire
gage progression across the break, when that would serve to smooth the
tension across the scale, in some cases, more than a half-size.

Frank Emerson
pianoguru at earthlink.net


> [Original Message]
> From: Thomas Cole <tcole at cruzio.com>
> To: Pianotech List <pianotech at ptg.org>
> Date: 12/16/2006 2:11:32 AM
> Subject: Re: Spreadsheet info / Jason Kanter
>
> A number of times I've rescaled for a stringing job and found that to 
> keep the tension even across the tenor/treble break, I would have to 
> make the low treble strings a half size larger than the upper tenor - 
> caused by the bridge lacking a dogleg going under the strut.
>
> We tend to think of speaking lengths as following a smooth curve, 
> because it's pleasing to the eye. If the bridge is being replaced, 
> though, why not let the speaking lengths float if you really wanted to 
> iron out the tensions? It would be fun to experiment to see if it would 
> be noticeable.
>
> Tom Cole
>
> RicB wrote:
>
> > Hi folks
> >
> > As you know Jason and a few friends are working on a spreadsheet for 
> > designing scales to share with the entire list.  He / we are trying to 
> > include a few specialized automation features and one of them is 
> > proving a bit challenging.  The idea is to try to provide some kind of 
> > way of automatically evening out tension as much as possible while 
> > maintaining a resonable string length curve and string diameters.  
> > Interestingly... the first attempts which floated diameters only when 
> > tension was all alligneed to an exact value....  resulted in a really 
> > weird (by usual standards) set of string diameters... with hops up and 
> > down in size all over the place.  Inharmonicity was not looked at (yet).
> >
> > Questions that arise have to do with what kind of range for variance 
> > in tension to scale designers typically operate with, and ... then I 
> > was wondering what really would be so bad about a scale that had 
> > diameters not necessarilly decreasing in size evenly up the scale... 
> > what would be wrong with a more ... jagged curve ?
> >
> > Jason is putting a lot of effort into this so any feedback would be 
> > greatly appreciated.  Any old scales you have stored for studying 
> > should be sent along to him.
> >
> > Cheers
> > RicB
> >
> >
>
>