was flat facts

[David Nereson]

Alan wrote:

> This question is so basic and naive, I fear the wrath of the list so I 
> will ask it annonymously ...
>  
> Customer asked: "I understand that humidity change is the principle 
> cause for going out of tune, but if it gets flat than sharp, etc., why 
> is the long term trend always flat?


   Because each of the 230-odd strings are at at least 100 lbs. tension 
and they stretch.  When they stretch, they go flat.  On a newer piano, 
other things are still settling, like the tuning pins settling in the 
bottoms of their holes, the bends in the piano wire gradually 
straightening out, the soundboard settling under the downbearing 
pressure, etc., and all those things combine to make the piano go flat.  
Now, many older pianos have strings that have pretty much stretched as 
much as they're going to.  Pretty much --  but those strings are still 
under tension and still stretching

> In other words, if it's a fact that the tuning pins are slowly turning 
> counterclockwise with playing and weather


   That's not really a fact, unless the pins are quite loose in the 
pinblock.  Stretching strings and other components settling into 
position, and the crown of the soundboard being pushed flatter by all 
the downward pressure contribute much more to a piano's going flat than 
pins turning counterclockwise.

> , why can't you just lock them in place, somehow, so the piano stays 
> close to pitch all the time?"


   Locking the pins in place wouldn't keep the strings from stretching 
or the soundboard from swelling and collapsing.

>  
> I stood there staring stupidly and could not conjur a 
> sensible-sounding answer.


   Well now you can..  PTG Home Office has one-page Technical Bulletins 
you can order and hand out to your customers.  There's one on Humidity 
Control and another on Pitch Raising.

>  
> What would YOU say?


   "Because the piano wire has been put under great tension and its 
natural tendency is to stretch and elongate under all that tension, so 
the pitch goes flat.  But sometimes humidity makes the soundboard swell 
up enough to pull the strings tighter and actually overcome the rate of 
going flat from stretching, but only for short periods of time.  When it 
gets dry again, or when the furnace comes on, then the soundboard will 
collapse a bit, letting the strings go flat again.  But over the long 
term, it's the stretching of the wire that makes the piano go flat.    
--David Nereson, RPT

>  
> Mystery Writer
> Salem, MO
>  
>
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>

I've read the comments that have been thoughtfully posted, but I have a 
very hard time believing that bridge grooves, string stretching, etc., 
will take a piano 50 cents flat in 10 years--especially if it's an old 
beater that has been crushing and stretching  for 75 years.

    I've seen pianos go 100 cents flat in 5 years.  Newer pianos, now, 
not old beaters. But I would not be surprised if I raised pitch to A440 
on an old piano that should have already done most of its stretching, 
then came back 10 years later to find it 50 cents flat.  In fact, I 
think it's happened to me several times.  Even on an old one that's had 
75 years to crush and stretch, if you raise pitch, you're adding more 
tension to the strings and more pressure to the top of the bridge.  It's 
gonna react because it's wood and stretchable metal, not concrete.
 
I agree with Sarah Fox; I think those pins are s-l-o-w-l-y turning; 
unwinding, if you will.
 
It's the only explanation that, to me, could account for such huge 
changes. If the strings were stretching, they'd be getting thin and I've 
measured enough old strings to know that, except when abused, they don't 
change /that/ much.

No, not that much, but they can decrease in size by a thousandth of an 
inch, which is one string size.  And yes, if the pins are a bit loose, I 
suppose they can unwind a bit, but I don't think it's the main factor in 
causing a piano to go flat. 
    Ever seen the becket sticking out of a pin a little too far, so you 
squeeze it in?  Does the pitch drop by just a few cents?  NO!  It drops 
WAY down!  It just doesn't take much at all to make a string go flat, so 
all those reasons above combined (string grooves, pins settling, etc.) 
are plenty to explain the pitch drop, even if the pins don't unwind at 
all.  It's an exponential, not a linear function, right?  Isn't pitch 
related to the square of the tension?  (IMHO)
    --David Nereson, RPT