Hello, Ron, Steve, Rick, Horace, and list --
Just the kind of response I was hoping for. I am much happier with larger
forces accounting for the motion up the pin. As soon as I saw Steve Brady's
contribution, the question of downbearing came much more strongly into play.
Instead of some motion of the bridge _past_ the bridge pins raising the
string (in wet conditions), why not a collapse of downbearing during dry
season, so the string had negative bearing? Of course it would want to rise
to neutral, which also explains why it wouldn't go up and up and up. It
would only go the minimal distance necessary to balance the negative
downbearing ("upbearing"?) against the increasing side-bearing of the
leaning bridge pin.
Please pardon me if someone already said all this, way back when. It's been
a really long, rich thread.
The string would also be urged up by hammerblows in heavy playing, though
that wouldn't be the main reason for rising, just an excuse for slipping
"up" there. It wouldn't go sharp, since in negative bearing the path
touching the bridgetop would be longer, not the one slightly in the air.
Once it was "up" there (really, at the same level as before, the board has
sunk away from it) vibration from playing would notch the pin, so it
wouldn't automatically go back down when humidity swelled the board again.
Actually, it only goes "up" by hanging a ride on the notch in the bridge pin
which it has made in the winter time.
Most of the time most of the strings would get back down off the pin when
the board rose again and restored downbearing. These things are erratic, and
don't happen to every note all the time. Only if the notch were sufficiently
"sticky" or deep would it stay up, and the greater the sidebearing the more
likelihood that it would stay up. (I believe that is consistent with earlier
postings to this thread.)
Staying "up" on the notch in summer (wet) would only increase the natural
tendency towards sharpness caused by the swelling board; as Ron has noted,
the path is longer when a string is off the bridge, assuming threre is
downbearing.
The trick now would be to take methodical downbearing readings, of the front
and rear lengths, in the problem section, of many pianos, over several
years, in areas with a strong seasonal humidity shift. (whew) Then one could
correlate near-neutral or negative bearing on _particular notes_ with the
"tick" of reseating, and see if it all adds up. The pianos would have to be
of good enough quality for really consistent sidebearing. That way one could
back up anecdotal evidence with something a little firmer. (And of course
_I_ can't do it: seasons are too genteel here.:->)
Don't know if this is a real answer, but I sure have had a lot of fun!
******************************************************************************
>At 05:38 PM 4/20/97 -0700, you wrote:
>>On Sat, 19 Apr 1997, Susan Kline wrote:
>>
>>> No, but I also have trouble with the humidity theory. (However, it's
>>> _remarkably_ original and interesting!)
>>>
>>> First, why has no one noted a difference in the need for string seating in
>>> wet and dry climates, or between buildings with good and poor
climate-control?
(Steve Brady:)
>> Actually, I have noticed that I have to encourage the strings on
>>my concert grands bridgeward each fall/winter. This seems to be mainly in
>>octaves 4-6. When I find that certain strings are becoming resistant to
>>tuning, I tap lightly and usually hear a "snick" as the string seats. The
>>string then tunes much more easily, and stays put better. I relate this
>>phenomenon more to tuning ease and stability than to false beats. I also
>>notice that the pianos seem much more stable in general during the spring
>>and summer than in the fall and winter.
>>
(Ron Nossaman:)
>I mentioned a while back that pianos tend to tune much cleaner and sweeter
in the summer when the humidity is up. I didn't specifically point it out,
but the inference was that tuners usually seat strings to cure unwanted
noises. It's done less in the summer when the noises are minimal, and more
in the winter when...
(Susan Kline:)
>> Third, has anyone noticed a difference in string seating in those brands
>> that have the bridge grain going a different direction? There should be one!
>> Vertical-grained bridges should swell higher than horizontal, shouldn't
>> they? Have they?
(Steve Brady:)
> My own suspicion is that there may be more expanding and
>contracting than just the bridge or bridge cap. How about the soundboard?
>Does it crown up enough in high humidity to produce this effect, or at
>least contribute to it? Would that help explain why I notice the effect
>more in the mid-treble than anywhere else?
(Horace Greeley answers:)
>>The answers here are yes, and yes.
>>
>>And I'm not sure why none of us have made an issue of this aspect before.
(Ron again:)
>As to why it happens more in the mid-treble, I have a few more ideas.
First, that's the area with the least downbearing (usually). Regardless of
what the manufacturer intended, that's what I find in practice. This might
be that it's the most likely spot to find the soundboard flat, generating
the retched noises that makes me take readings in the first place. This
may/not be a factor. Second, the string section between the rear bridge pin
and the aliquot, or hitch, is closer to being the same length as the
speaking length in the mid-treble as anywhere else in the piano. The
downbearing forces are more balanced. The shorter the moment arm, the faster
the bearing angle changes with bridge elevation. In the bass and low tenor,
the bearing angle changes on the back of the bridge much more than on the
front with a humidity cycle. Maybe this (and more vibrating string mass)
pulls and jiggles the string back down on the bridge as it dries and
shrinks. In octave 5 1/2 - 6, the forces fore and aft are more evenly split,
and the string mass is considerably less. I think string mass probably has
more to do with it than anything else. Thoughts?
(Richard Moody:)
>>Granted there is no zero friction execpt in the imaginary. So in
>>reality does the pitch vary less wildly as the string renders less
>>freely through the pins according to how much friction is present?
(Ron Nossaman:)(4/21/97)
>Yep. Given a well tuned, stabile piano. I've noticed on some instruments, a
heavy blow will knock a string slightly flat. Following up with a lot of
light to medium blows, the string will creep back up to pitch! I'm assuming
the now overtensioned tail section is pulling the string back through the
bridge until the section tensions equalize. This doesn't work on all pianos.
Some just don't render through the bridge easily enough to noticeably
produce the effect. Like everything else relating to this discussion, and
pianos in general, it's a matter of degree.
(Susan Kline:)(4/19/97)
>I worried, a long time ago, about whether lubricating bearings to improve
rendering on uncooperative pianos would ruin pitch stability by lessening
friction, allowing pitch swings such as you describe. So far, the answer has
been that there's still enough friction for stability, and it's better to
render more easily -- you get a "self-healing" effect as the unequal tension
from the worst blows finds its own way back through. How low a level of
friction the system would tolerate, I don't know. Surely other people know
more about this than I do?
____________________________________________________________________________
To answer my own question: yes, they do, isn't it great?
It still seems like a good idea to lesson bridge friction (somehow or other)
for tuning stability, when it is a problem.
Still not sure if there is any way to lessen the need to seat strings, other
than controlling humidity.
CA glue around the pins still seems a good idea, for good terminations,
whether or not the string rides up. The worse the humidity swings, the more
important firming the pins and protecting the wood from moisture would be.
Would CA glue around the pins protect the wood enough to explore other
lubrication than just graphite?
Signing off, unless some wonderful new notions appear!
Susan Kline
skline@proaxis.com
P.O. Box 1651,
Philomath, OR 97370
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