Unison Flatter than each Individual string?

[Tom Servinsky]

>> > > It may be that the machine is fooled.  Who first noticed this
> > > "phenomenon" ?  a machine tuner or an aural tuner?
> >
> > It is my understanding that Virgil is given credit for
> > noticing this first.
> >
> > RicB
>
> Then it is easy.  How many aural tuners notice this and care to
> demonstrate it to other tuners?    Unless this is can only be
> shown on certain "high tension scales"  methinks it would have
> been noticed 100 years ago.  ---ric
>
Ric and list,
First I'm not a physicist commenting on this phenomenon but a very strong
aural tuner who uses an SAT  for comparison tuning. My findings. aurally and
electronically, through the years seem to concur that 3 strings tuned
together as an unison can and many time result  in a combined different
pitch. But not necessarily a flatter result.
One of the ways I stumbled upon this was one time I  decided to tune a piano
using no felt temperament strip ( instead of my usual method). This was at
the encouragement of Bill Garlick, who for many years advocated tuning in
this method. In Europe this is the way the better tuners were taught to
tune. So time was not an issue on this one day and my candidate was on a S&S
concert instrument that I had tuned weekly. I knew the way the piano tuned
intimately.
That being said, the resulting tuning I arrived at was superiorly   much
cleaner and more harmonious sounding than with my usual aural method. At
first I thought it was dumb luck but as I experimented with my tuning
methods (aurally and electronically) I kept  noticing that the tuning (many
times but not always) improved if  all 3 unisons were tuned as I progressed
through the temperament. The resulting tuning represented a better
presentation of octave stretch which agreed with the piano  better vs. if I
used the felt  strip muted the piano. Why. At the time I wasn't sure but
then I used the SAT to justify my thoughts and sure enough there was some
justification of what I was experiencing.
Take any 3 strings of an ordinary unison and measure electronically the
readouts of each of the 3 strings. Many times the numbers are different. I
remember Dr. Sanderson commenting on this as well, stating that if you want
to get a better and more representative FAC tuning, measure your 3 notes
with the unisons being tuned first and average them out. And sure enough the
FAC tuning benefited as well.
Why. My theory leads me to think that bridge notching and string speaking
length have a lot to do with it. Bridges notched inconsistently will/can, in
theory,  yield slightly different speaking lengths and thus effect the
unison  quality of any given note. Essentially the strings can be out of
phase and begin to have a canceling out effect. Mind you these are minute
differences, but differences none the less.
Do all pianos do it. I'm not convinced. But many do and enough so that my
more serious concert tunings get the special treatment and unisons are tuned
as I go.
As far as Ric's comment on why wasn't this talked about 100 yrs. ago, well
according to Bill Garlick it was. Which is why places like the Bosendorfer
factory taught the tuners to only with a single rubber mute. It yielded
better results.
So there you go, one anal retentive aural tuner's take on the matter.
Tom Servinsky, RPT