rehearsal room to theatre stage

[Tvak@aol.com]

Piano in question: Yamaha P2.  This piano has been in the rehearsal room at a 
local theater for 15 years and I've been tuning it for about 5 years.  This 
past week it was moved down to the theater stage for a production where it 
will be used as the performance piano in the onstage band.  

I am shocked at how much this has changed the piano.  Suddenly the strings 
don't render easily; in fact, one broke, not at the becket but at the 
pressure bar.  My tuning efforts yesterday were very difficult as the string 
would stay, stay, stay, and then with one tiny movement of the pin, shoot way 
sharp, past the target.   

In addition, the tone is strange on some strings.  D5, D#5, and E5 for 
instance, sound as if there are two sizes of strings on the same unison.  
There is a metallic-ness to the tone and the unisons don't sound pure---none 
of the strings in these unisons have any false beats, but together they 
sound...well...funky.  This was certainly not apparent in the rehearsal room.

In addition, true false beats have also appeared throughout octaves 6 and 7.  
(Is that an oxymoron: "true false" beats?)

None of this was the case when the piano was in the rehearsal room.  The 
humidity is higher in the theater; I measured it at 47%.  (I believe the 
humidity in the rehearsal room was closer to 30%.)  I'm sure that the 
temperature on stage varies greatly, from performance-hot, to the 65 degrees 
that it was when I tuned it yesterday.   

So, today, I'll go in and CLP the strings at the pressure bar, seat the 
strings to the bridge in the treble, and re-tune.

I'm sure that the humidity must be the culprit behind the changes I've seen, 
but why/how would it change the timbre on those notes?  Why the difficulty 
rendering the strings?  (Rust couldn't form in 47% humidity in one 
week...could it?)

Tom S