Rescale treble

[Delwin D Fandrich]

Roger Jolly wrote:

> Greetings Del,
>     I have just got a 5'8" no brand name piano in on trade.
> Obviously a lower grade PSO but the board and bridges are in great shape.
>     I have had a mind to try and control forward termination harmonics for a
> number of years and as this unit is mine, a screw up will just cost me time
> and material.
>     I am thinking of grinding off the rear pressure bars in the casting,
> and replacing them with short 1/8" half round stainless steel bar. My
> theory being that if it is tuned to a) a compatible harmonic and b) all
> three unisons are in tune with each other, a more round and stronger tone
> quality will result.
>     A number of years ago I had suggested to Harold Conklin to make the
> treble temination resonators, on the SD10 out of Nymonic steel. Cost wise
> it was off the wall, but the result was case hardening of the previously
> mild steel items. The result was a great improvment in projection, and very
> little wear to the resonators over along period.
>     Several questions you may be able to help with...
>     1. Have you tried some thing like this. If so what did you learn?
>     2. The top note I have enough room to tune the forward duplex to the
>         octave, is it worth a try.
>     3. Any suggestions an a pattern of harmonic conponents to try for.
>     4. Any prefferences re. 1st 2nd 3rd 4th harmonic and in what range etc.

> Any help would be greatly appreciated
> Regards Roger Jolly.
> Roger Jolly
> University of Saskatchewan
> Dept. of Music.

- - - - - - - - - - - - - - - - - - - -

Roger,

I'm kind of the wrong person to ask for advice about tuned duplex, or aliquot, systems. I'm not
convinced that tuning the back duplex string segment is of any practical acoustic value. Please
refer to the two articles I've already written on the subject. They're in the June, 1995 and August,
1995 Journal.

Generally it is my opinion that the back scale string lengths -- i.e., the string segments between
the back bridge pins and the counterbearing bars, whether tuned or not -- that are found in most
pianos are too short. When developing a new scale I do typically use some fraction of the speaking
length (Ls) as a guide. While in theory this does result in a more-or-less "tuned" string segment, I
use these ratios primarily for computational convenience. The resulting back scale lengths are what
I consider to be the acceptable minimums. Following these guidelines will result in a back scale
that is somewhat longer than is normally encountered. But, in my view, lengths shorter than these
tend to restrict the motion of the bridge excessively. Typically this schedule is as follows: Ls/1.0
for unisons #79 through #88, Ls/1.5 for unisons #69 through #78, Ls/2.0 for unisons #60 through #68
and Ls/2.5 for unisons #51 through #59.

When rebuilding a piano with a tuned duplex back scale -- assuming that we have the freedom to
improve on the original design -- we will do one of two things: In some cases, if the plate is
deemed strong enough, and if other factors such as the geometry of the system are favorable, we will
convert the hitch pin system to vertical pins. If, for a variety of reasons, we decide that this is
either not practical or not possible with a specific plate, we will then move the counterbearing
bars back toward the hitch pins to achieve a back scale that is as close to these dimensions as we
can get. If the back bearing bar is cast in place, we will grind it away and replace it with either
an appropriately sized brass half-round or half-oval bar. Within limits, I'll try to get as much
back scale length as I can.

Working with the front duplex is another matter. Without seeing the actual configuration of the
plate you are working with, I don't know specifically what to advise. Here also, I'm not a fan of
the tuned duplex system. Typically (and again, assuming we have the option from our customer) we
remove -- by grinding, if necessary -- the front counterbearing bars and replace them with half-oval
brass pieces that are placed as close to the capo-'d-astro bar as is practical. Exactly how this is
done is hard to explain here since the precise technique varies from one piano to the next depending
on the plate design. The idea is to get a string deflection angle that is greater than 20 degrees
and to keep the duplex string segment as short as is practical.

I have tried to explain my reasons for the above in the two articles mentioned earlier. If, after
going back and reading those, you still have questions, let me know. I'll be happy to answer general
questions as I can through pianotech. For specific advice about a particular piano... well, I do
work as a piano design consultant from time to time.

While I realize that all of this probably isn't the answer you were expecting, I do hope it helps
some.

-- ddf