[CAUT] IRe: Unison drift (was Reading low humidity/seasonal SB failure)

[Chris Solliday]

how about tuning from the bottom up then checking with the machine from
bottom up then checking by ear? I doubt you'll notice the same detail in
drift by ear that the machine will find but I do like listening to the
corrected tuning and occasionally making an "aural improvement." I recommend
the DOB assisted tuning with an Accu-Tuner and so does Dr Sanderson. Chris
Solliday
----- Original Message ----- 
From: "Greg Newell" <gnewell at ameritech.net>
To: "College and University Technicians" <caut at ptg.org>
Sent: Tuesday, March 07, 2006 10:29 PM
Subject: Re: [CAUT] IRe: Unison drift (was Reading low humidity/seasonal SB
failure)


Fred,
         First I'd like to thank both you and Ron
Nossaman for your patience in explaining why you
fret as much over the humidity changes as you do.
It does seem that you can make rather astute
predictions in the resultant outcome of a
seemingly minute climactic change. Admirable!
         I have to wonder about why I don't see
anywhere near the left, center, right string
discrepancies that you do. While the pianos in
the university that I serve do go rather
drastically out of tune with the change of
seasons (abominable building) I still don't see
the unison problems that you do. Those kinds of
differences would make the pianos sound rather
hideous wouldn't they? I may get that much rise
and fall but it's mostly together over the three strings of the unison.
         I cannot dispute your observations about
the bridge pins but I also have to wonder if
tuning sequence plays some part in it or not. Do
you use any electronics? If so how do you use
them. If the piano is in a practice room would
you ever feel comfortable enough tuning from the
bottom up by machine and then checking the end
result aurally? Seems I remember that Al
Sanderson maintains that better stability is
achieved this way. Also, how are these strings
rendering across bearing points? If you tuned
with a temperment strip and then tuned in the
outside strings after setting bearings then you
could be setting up different tensions in the
wires even though they sounded fine when you were
done. This could be especially prevelant if the
strings weren't rendering all that well.
         I'll quit while I'm behind here and
patiently allow corrections from the list. Thanks fellas (and ladies too).

best,
Greg




At 08:13 PM 3/7/2006, you wrote:
>On 3/6/06 4:45 PM, "Dorothy Bell" <dabell58 at earthlink.net> wrote:
>
> >
> > Dear Fred,
> >
> > I'll bite: what mechanically would make the unison drift with that
> > particular triplet pattern? I tuned a home piano this morning which was
in
> > exactly that situation after having been tuned at much higher RH five
> > months ago. Somewhere recently I read that 'if the pitch goes out, it's
the
> > humidity; if the unisons go out, it's the tech.' I'm certainly willing
to
> > take responsibility for all the griefs of man, but it doesn't make sense
to
> > me that unisons going out in a very specific pattern, in a very specific
> > part of the piano, would indicate poor hammer technique. When I look at
the
> > piano, though, I don't see what would cause the consistent flat-sharp
> > changes.  Can you advise? Thanks.
> >
> > Dorrie Bell
> > Boston, MA
>Hi Dorrie,
>     The short answer is "I don't know." I do know that the phenomenon
>exists, repeats, and I have come to believe that it probably occurs on all
>pianos. The very short term effect on the concert grand from a rain storm
>shortly before I have observed multiple times. It's rather subtle: the
piano
>has just "gone sour.'
>     But after longer and more extreme humidity changes (in either
direction)
>a more obvious and quite striking pattern happens. It varies in degree with
>model of piano. In my own stable (or should I call that "in-stable"?),
>Yamaha G2's take the cake. I'll find unisons in the mid-high treble with
>left string 10 cents flat, right string 15 cents sharp, middle string close
>to pitch. Lots of them. I have observed this pattern on a wide variety of
>pianos, including uprights. It isn't absolute - every single unison
>exhibiting it - and it varies from section to section, but it seems to be
>consistently there. In all cases, I believe, the treble-most string moves
>the farthest in the direction of humidity change (ie, up with rise in RH,
>down with lower RH).
>     As I have puzzled over this for 15 years or so, I have come to a few
>tentative conclusions. First, I have decided that probably the tuning pin
>pattern doesn't play a major role. I'll list three pretty strong reasons:
>1) The phenomenon happens in both grands and uprights, with the same left
to
>right relationship. Pins on grands and uprights are mirror image in terms
of
>distance from speaking length. If that variance in distance were a major
>factor, the pitch difference should be opposite as well.
>2) Steinway B's (and a few others) have a particular tuning pin pattern
>we're all familiar with. If distance from speaking length to pin were a
>factor, we should see a significant variance from unison to adjacent
unison,
>and particularly from the closest of a pattern of six pins to the farthest.
>I have looked for such a pattern and have failed to find one.
>3) I have observed this phenomenon on a Wurlitzer grand with a Wegman plate
>(no pinblock). Hence, no swelling or shrinking of pinblock could play a
>role, at least on that piano.
>     What does that leave? Well, there is no typical pattern of back
lengths.
>That leaves the bridge. Particularly the notching pattern, with the treble
>most pin closer to the center of the bridge, the bass most pin closer to
the
>edge. This pattern holds for both uprights and grands. What could the
>mechanism be? Well, it's a bit counterintuitive. The way I figure it, the
>pin closer to the edge of the bridge migrates (with lateral expansion of
the
>bridge) in the direction of the speaking length more than the pin that is
>closer to the center. Hence, it makes the speaking length (or tension) that
>little amount less, counteracting the overall rise in pitch from soundboard
>rise, etc.
>     I won't say I believe this is the answer, but it's the best model I
have
>been able to come up with. Jim Ellis believes it to be more to do with
>tension variance due to greater or lesser side bearing of the string
>crossing the bridge between the two pins. Either way, that doesn't seem to
>be enough to account for it. OTOH, I think most of us have experienced that
>strange pitch change that happens when a string breaks. The immediate
>neighbor strings go sharp by a significant amount. What can possibly
account
>for that? Very minute changes in down pressure on the bridge, and side
>pressure through those bridge pins. If such seemingly minute changes can
>cause a measurable pitch change, then maybe the bridge model I described is
>the key to unison change caused by RH change.
>     But this is all very hypothetical. I would welcome other models, and
>other people's observations. Maybe I am wrong, and this isn't as universal
>as I think. It is harder to observe in private homes because I'm not there
>enough to know for sure what happened since the last tuning. So my main
>observation is limited to the models I have at the university.
>     One thing I am pretty certain of: Unisons go out of tune in response
to
>RH change. It's not always lack of skill on the part of the tuner <g>.
>Regards,
>Fred Sturm
>University of New Mexico
>
>
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Greg Newell
Greg's piano Forté
mailto:gnewell at ameritech.net


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