[CAUT] Pitch drops on individual strings

[Joseph D. Gotta, RPT]

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 You said that the pitch moved significantly with firm play. This tells
me that there is movement of tension across termination points. Try
seating the strings at the back side of the bridges first, then the
front side. This will help to equal out the tension as well as firm up
the bridge contact to restrict movement. Check the plate bolts too. If
they are loose and the piano is moved the plate could shift enough to
affect the tension relationship between the back scale and the speaking
length. Whatever the case tell the customer it's the humidity and see if
you can make a DC sale. 
 
Joseph D. Gotta RPT
 
-----Original Message-----
From: caut-bounces@ptg.org [mailto:caut-bounces@ptg.org] On Behalf Of Cy
Shuster
Sent: Saturday, May 21, 2005 8:22 PM
To: CAUT
Subject: [CAUT] Pitch drops on individual strings
 
I'm seeing some strange pitch drops in individual strings, and I can't
figure out why.
 
First, the history.
 
This is a 1974 Yamaha C3, in pretty good shape, in the large band room
of a community college, with central HVAC.  No D-C on the piano.  Three
weeks ago, we moved it overnight to two different off-campus locations
for the spring concert series (half an hour ride in a pickup truck each
time -- yikes!  I covered it up, but still...).  It's had five tunings
in the last month, and I've recorded humidity each time.  I use TuneLab
Pro, and used the same stored tuning each time.
 
The series ended May 1, and I tuned it just before that concert.  It
survived the concert sounding good; no slipped unisons.  It's been in
the same spot for three weeks, uncovered, lid down.
 
Now, the mystery.
 
On Tuesday, they asked me to tune for a recording the next day,
mentioning that a few unisons were out in the top two octaves.  I
measured all the A's before I tuned (as is my habit).  A4 and below were
right on, except A1 and A2 were up about two cents (humidity is rising).
A5 was up 3c, A6 down 6, A7 down 3.  I noticed that in many treble
unisons, one or two strings would be way off: either a string would be
right on, or off by a considerable amount (is it my string-settling
technique?).  I also noticed that many strings would move a lot if I
pounded on them, before touching the pin.  I worked hard on those top
two sections of the plate, making sure every string was well settled,
and wouldn't move.
 
Yesterday, they called me back to tune their other piano, and also
mentioned that the top two octaves were out on the Yamaha again (!).  I
checked it, and A2 and below were spot-on, as were A6 and above.  But in
the middle three octaves, a dozen notes had one, two, or three strings
off by two or three cents (A4 was down five cents!).  All but one were
flat.  Again, either a string would be exactly in tune, or off by a lot.
I checked the pitch of every string before I began to tune, and
chalk-marked the tuning pin of each string that was out (for next time).

 
They did mention that they turned off the A/C in the room for the
recording (because of noise), and then fired it up full blast during
breaks.
 
Here's the temp/humidity record (graph attached).  Humidity was lower in
the two off-campus locations, and has climbed steadily upwards.
 
4/10: 72F, 42%
4/17: 68F, 32% (off-campus)
5/1:   68F, 39-41% (back home; last concert)
5/17: 72F, 44-48%RH. 
5/20: 72F, 55%
 
By the way, the other piano didn't exhibit this symptom of individual
strings falling, and others staying right on.  This is really the heart
of the mystery to me.  My experience with pitch swings from humidity is
that it affects strings evenly.  The other piano is a D in a different
room, with similar humidity, also last tuned 5/1.  It was sharp a few
cents evenly across the middle, dropping down to -10 in the top octave.

 
Maybe it is my tuning lever technique?  I usually finish a string by
coming down to pitch, to make sure the pin has no residual torque; maybe
I'm leaving some tension in the front string segment that settles back
to the speaking length during play, or humidity changes?  In writing
this history, I notice that the top two sections that I worked hard on
Tuesday night were still fine; the problems I found yesterday were lower
down.
 
The other possible suspect is loose bridge pins.  Earlier I had noticed
a consistent drop around A6 on some strings, and found I could slightly
move a few leading bridge pins with screwdriver pressure.  How this
would lead to pitch drop, I'm not exactly sure...
 
--Cy Shuster--
Bluefield, WV
 

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