[CAUT] Pitch drops on individual strings

[Ed Sutton]

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Cy-
I would call this humidity related until you find out otherwise. Just IMHO.
I've encountered some C-3's that seemed very sensitive to humidity change.
Ed Sutton


----- Original Message ----- 
From: Cy Shuster 
To: CAUT
Sent: 5/21/2005 8:20:20 PM 
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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