More Scaling Questions

[Jim Coleman, Sr.]

Hi Stan:

I could have answered last week, but I assumed others would be jumping right
in.

The main reason for changing from 3 string unison plain wire in the lower
tenor section to 2 string wraps is that many scales have such a 
foreshortening of string length in that area that the tension drops 
considerably and the inharmonicity rises likewise. By changing to wound 
strings, the tension is increased, the inharmonicity is lowered and you
can have a smoother transition across the break to the Bass section. I like
to at the same time attach an auxiliary bridge stock to that tenor section
in order to also shorten those wound strings to avoid too high tension.

The first piano which I laid out was made with the idea of perfectly smooth
inharmonicity. The second piano also was done this way. I have come to 
believe that it is better to balance the two curves. If inharmonicity is
the supreme consideration, then there are larger jumps in tension at each
wire change location (usually 10 to 12 pounds). By balancing the 
inharmonicity curve and the tension curve, these jumps are minimized and
there is a smoother voicing relationship. I think also that the tuning
stability is helped.

The Pscale program has an automatic facility which will fill in for you
some rather ideal diameters and wraps for the Bass section. I usually do
my own selections, but Tremaine Parsons has made that available to you as a 
guide if you like. I have in the past written several spreadsheet programs,
but I like his program best because it is graphically interactive.

You can't have everything when it comes to string contact time, 
inharmonicity, tension, percent of break strength. You must make some calls
of your own.

Jim Coleman, Sr.

On Mon, 1 Jun 1998, Stan Kroeker wrote:

> Just in case the following query did not come through the list when I
> posted it last week, here is a repeat.  If it did come through and there
> were simply no takers, my apologies for wasted bandwidth.  (SK)
> 
> >Since David Roberts' book, The Calculating Technician, was published some
> >years ago, I have programmed his formulae into a spreadsheet and plugged in
> >the appropriate data from each piano I rebuild.  The data from the various
> >functions he developed (Loudness Factor, Hammer/String Contact Time,
> >Inharmonicity of the 4th Partial, Tension and Percentage of Breaking
> >Tension) creates some impressive graphs of each function, but I haven't yet
> >learned how to manipulate this data to optimize the scale on a given piano.
> >
> >I understand that others use Dr. Sanderson's formulae for scale analysis
> >and some feel that they are more accurate, at least as far as calculation
> >of tension and breaking percentage go.
> >
> >Although I have been told that the scaling software that is currently
> >available is suitable (at least for those of you with Windows based PCs), I
> >would like to take the discussion of Do-It-Yourself scale analysis to the
> >next level.
> >
> >Would those of you who have modelled their own spreadsheets with either
> >Roberts' or Sanderson's formulae care to comment on your procedures?  Which
> >functions take precedence?  Smooth tension curve?  Smooth inharmonicity
> >curve?  How do you actually manipulate the data?  Do you identify problem
> >areas on the graphs and just empirically change wire diameters to see if
> >there is any improvement?
> >
> >There is a fascinating article in the June 1988 Journal on 'Rescaling the
> >1905 Steinway Upright' which involves replacing the lowest 2 tenor trichord
> >plain wire unisons with copper-wound bichord unisons.  The article mentions
> >the Sanderson formulae and gives the reasons for recaling but doesn't
> >actually get into the procedure.
> >
> >Suggestions?  Experiences?
> >
> >Best regards,
> >
> >Stan Kroeker
> >Registered Piano Technician
> >
> >Kroeker & Sons Piano Experts
> >59 Quiring
> >Winnipeg, Manitoba
> >Canada  R2G 1Y5
> >
> >Ph. 204-669-5881
> 
> 
>