The fact is, that pianos DO and WILL change relatively quickly and very easily from humidity changes. Especially when they have been rebuilt or are new.
A change from 70 % in August to 38 % in November is a large change. It is 50 % less of what it was in July. Of course, the piano will be flat and out of tune with itself because of this. And yes, hammer flanges can come loose.
Jerry: These figures are the extreme 'spikes' in a daily-fluctuating long-term trend, not the the trend-line itself. While such figures may have been registered for a few hours
in total over the course of 5 months, the decline from around 65% to 45% represents the more enduring state of affairs. Of course, that 20% shift may be sufficient to precipitate problems, but if so, then I'd expect that there are quite a lot of other new and rebuilt pianos 'settling-in/falling-apart' out there. Yet that doesn't appear to be the case to judge by others responses to experiences of 'settling in'.
Of course, it is a gradual change. That is pretty typical. Here in Michigan, in August it can easily be 70% RH. In September, it will be in the 60 % range, continuing down as the cooler weather continues.
A piano is made primarily out of wood. I read once years ago, that during the average summer in Michigan, the wooden frame of a door in our home will swell by 1/4". During the winter time, that same door, shrinks by that much AFTER it looses the 1/4" that it gained by swelling in the summer. It is no wonder that our drawers, doors and windows will sometimes stick.
Just because they are painted doesn't mean they are no longer capable of absorbing humidity.
As a piano owner, if you want your piano to maintain its best, it is your responsibiltiy to do whatever you can to maintain a fairly constant relative humidity (RH) where there piano is located. By that, I don't mean between 70 % and 35 %. I mean, between 40 % and 50 %.
All technicians receive complaints constantly that my piano was just tuned but now it's out of tune. In looking up our records, we see that it's been 4, 5 or 6 months since its last tuning when the RH was double or triple of what it is now. The biggest argument I get from my clients is "well, that shouldn't happen!" Why not? "I don't know, but, it JUST SEEMS like it should stay in tune longer." It is a lack of understanding about what actually takes place with the wooden parts and the causes of why a piano goes out of tune and why piano manufacturers recommend tuning your piano between 2 and 4 times every single year as a minimum because they all know that the piano will indeed go out of tune often under these ever changing humidity circumstances.
Jerry: The piano was tuned on a monthly
basis, during which time the RH would have reduced by around 5% per month on average if we flatten the trend line. In fact, however, on the the first and second, and fourth and fifth tunings, there was little change in RH, the main decline having taken place between the second and fourth tunings. Yet still it went south very quickly after all tunings, not to mention all the other problems.
In short, I find it hard to believe that 20% shift in RH over 5 months could effectively wreck a new piano. If that was the case, then I don't think there would be too many pianos in the world today.