Understanding Duplex Tuning and placement.

[Phil Bondi]

Today I tuned a Yamaha C7 for the 3rd time this year. The piano is a
wonderful instrument, and a good candidate for my experiment. The experiment
being..I wanted to find out what notes were being sounded a certain part of
the duplex section..and why. I kept my sample section small - I only sampled
the notes from B4 to F#6, which on this piano covers from strut to strut of
the upper tenor/lower treble section. I did the experiment after I was done
tuning. Here's what I found:

The 'sound' or the 'notes' being 'excited' in the duplex section don't make
any sense to me. I really want to understand this to better understand why a
piano sounds the way it does, or doesn't, depending on your perspective.

Hopefully, the following chart will make it through so anyone reading this
will understand it..the first note will be the actual note on the piano, and
the second note will be the 'sound' coming from the duplex when plucked. The
+ or - in the parenthesis following represents where the duplex sound is in
comparison to the actual tuned note..+ = sharp ..- = flat. If there is no +
or -,  then, to my ear, it was in tune, or really really close where I
didn't think there was a measurable difference.

Here goes:

B4 - C#7(-)
C5 - D7(-)
C#5 - D#7(-)
D5 - E7(-)
D#5 - F7(-)
E5 - F#7(-)
F5 - C#7(+)
F#5 - D7(+)
G5 - D#7(+)
G#5 - E7(+)
A5 - F7(+)
A#5 - F#7(+)
B5 - G7(+)
C6 - C#7
C#6 - D7
D6 - D#7
D#6 - E7
E6 - F7(+)
F6 - F#7(+)
F#6 - G7(+)

You'll notice at F5 and C6, there was a big change in the duplex note from
the previous note..this is where the hitch pin configuration changes, also.

The recent thread on Duplex tuning only had me mildy interested because,
frankly, I was real busy with other things..but I remembered it and it got
enough of my attention to try an experiment when time allowed.

For those that don't know, the C7 has a similar "Steinway-style" duplex
configuration, as opposed to Baldwin's older individual aliquots.

I would think that the sound coming from the duplex would better represent
something from the partial series for that particular note..that's what I
"think"..that doesn't necessarily mean I am correct or I'm even close..I
know very little about Piano Manufacturing or how a piano gets scaled,
and/or why..I am interested in finding out why these particular notes'
duplex sound what they sound..and are they correct..and if they're not
correct, how does one correct them after a piano is tuned and not mess up
the tuning, and shouldn't you tune the duplexes AFTER you've tuned the piano
and won't that mess up the tuning?!?

With this type of configuration for a duplex, how can you effectively change
one duplex without changing all of them, to a certain extent?

Having recently re-built a Baldwin R with the individual aliquots, I can
understand how and why that system might work a whole lot better now than I
did when I re-built that R. So..how can you effectively change the duplex
sound for one of the 'Steinway-style' duplexes and not change all of them?

Am I out in Left Field?..did I have too much time on my hands this
morning?..is there any validity in what I am asking?

Phil