[CAUT] Detuning phenomenon; was: How long to stabilize??

[Andrew Anderson]

I would tend to agree with Jeff Tanner that pianos do move quickly  
with humidity changes.  I tell customers that pianos go out of tune  
just about as easily as guitars do, but that they are equal to about  
fourty guitars in work when tuning.

I would add that there are smaller but definite moves that take longer  
to happen with a humidity change.  l also own a small piano store and  
get to observe pianos that have been in warehouses then in trucks  
acclimate here in the store.  My experience is that the largest moves  
happen within 12 hours or less.  After that more subtle yet  
significant moves take place over the next three weeks.

I come to piano tech from business as a journeyman timberframer (log  
frame as well).  I suspect that some of that latter movement is  
lengthwise movement along the grain rather then the usual culprit,  
cross-grain movement.  This is an issue we had to plan for in timber  
and log frame.  Green logs could shrink lengthwise over an inch after  
install.  (Yes they were long.)  Such movement would have to be  
planned for or the warranty situation could get rather "sticky".

In the piano this can translate to changes in tension support along  
beams etc.  I have suspected, as noted here, that the unison smear in  
opposite directions has to do with slight position changing of the  
bridge due to the shape of the piano at that end of the scale.  I do  
note this pattern more on the high end of the piano then on the lower  
end.  It would be interesting to take precise measurements from the  
plate to the bridge at different points in the scale with 10 to 40  
point RH changes.  Perhaps tuning pin to bridge measurements would be  
better as there probably is some slack in the pin too.

Sincerely,
Andrew Anderson

On Feb 20, 2009, at 11:18 AM, Jeff Tanner wrote:

> Hi Daniel,
> Our recital hall at S Carolina experienced very similar results as  
> those you observed.  My tuning time in the hall was originally first  
> thing in the morning as had been established by my predecessor. It  
> didn't take me long to learn that what I tuned in the morning had  
> often dissipated by the time the recitals began at 4:30.
>
> In response to your statement below, I'd like to throw in my  
> observations. Perhaps I am misinterpreting your perspective.  In  
> South Carolina, we really never experience a gradual change in  
> humidity.  It's not there one day, the next day it is here, and here  
> to stay (except for during the school year, of course, which can  
> reveal 55% today, 27% tomorrow, 48% the next, etc).  But once the  
> end of the school year rolls around, we've generally and literally  
> jumped to 60%+ RH (in the humidity "controlled" recital hall --  
> rooms with no humidity control and occupants who sweat profusely at  
> 65 degrees would see RH as high as 80%RH and just below), and it  
> remains there until late in the fall semester, when it simply  
> nosedives after Thanksgiving just in time for juries.  What I  
> observed during the summer months in the recital hall, even after a  
> month or so at the upper end of the humidity range, is that the  
> pitch continued to climb, even having "stabilized" the instruments  
> for a week during July for a piano festival.  The pitch continued to  
> creep upward through September before it began to stabilize, and  
> that perhaps only because we were tuning again on a regular basis,  
> holding the pitch down.
>
> I also observed one occasion in the recital hall when I felt and  
> smelled the humidifier come on during a tuning.  I watched as my  
> hygrometer lying on the piano began to change numbers like tenths  
> digit on my car's odometer going down the interstate.  I also could  
> measure the pitch changes minute by minute as the humidity  
> increased.  I stopped tuning, put my tools in my bag, and went and  
> reported the obvious malfunction.
>
> So, I'm not quite sure what you mean by 3 days.
> Jeff Tanner
> ----- Original Message -----
> From: Daniel Gurnee
> To: Ed Sutton ; caut at ptg.org
> Sent: Friday, February 20, 2009 11:33
> Subject: Re: [CAUT] Detuning phenomenon; was: How long to stabilize??
>
> Humidity wise, it has been generally understood  that humidity will  
> affect wood by three days.

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