Strange partials

[Jim]

Hi David:

Bass strings can do some weird things. Especially when there is uneven
loading anywhere in the string.  Some of the worst examples are where
at the starting end of the copper wrap, there is a double thickness of
copper for about and inch.  It was discovered many years ago that extra
loading at the ends will greatly reduce the inharmonicity of a string.
However, it does not do this evenly.

Several companies have utilized this type of string making with the idea
that reducing inharmonicity is the ultimate goal. At the University where
I used to work, there is a Steinway O which has that kind of Bass
stringing.  Many Yamaha pianos of 20 or 30 years ago used that type of
bass strings. I don't remember seeing this on Kawai pianos.  Is this by
any chance the kind of strings you have on the K20 you recently tuned?

If there is enough interest, I will make some graphs for the list which
show the typical deviation from normal inharmonicity patterns so that
what I am talking about will be more obvious. Oh well, for now here is
a description of the type of string I am talking about (in ASCII art).


                                   ----------
      -------------   ------------/ ----------\
-------------------   ------------------------------------ to Loop-->
      -------------   ------------\ ---------/
                    ^              ----------
      C             |               A         B
                    |
                    --- obvious removal of much of the string length
                        for illustration purposes.


The center line going to the loop represents the core wire. The winding
starts at point A going toward point B where it reverses direction,
climbing over itself.  It locks in the winding so that it cannot become
loose at the swedging of the core wire.  When it gets back to point A
it drops down in contact with the core wire and continues on to the end
of the swedging at the front end of the string at point C.

With strings of this type it is quite possible to find negative inharm-
onicity for several different partials.

Even with normally wrapped bass strings, one can notice erratic behavior
of the first 2 or 3 partials.  It is my belief that this would not happen
if the winding passed through the Agraffes and bridge pins, but with the
extremely high tension of piano strings, we cannot get away with this
as they do with guitar strings, violin strings etc.

Jim Coleman, Sr.


On Thu, 17 Apr 1997, David M. Porritt wrote:

> Today I tuned an older Kawai "K20" studio piano.  The bass could not be
> tuned smoothly.  I was tuning aurally and finally when I got to A2
> decided to check the partials with my SAT.  I set the 4th partial of A2
> to A4.  There was still a lot of beating going on.  I decided to measure
> the 6th and 8th partials to see how sharp they were causing all that
> racket.  They were flat!  How do partials that high get flat?  That is a
> consumate pain to tune and I do it a couple of times a year.
>
> Any clues?????
>
> dave
>
> _______________________________________________
>
> David M. Porritt, RPT
> Meadows School of the Arts
> Southern Methodist University
> Dallas, Texas
> _______________________________________________
>