The whole issue of how to quantify the effect of humidity swings, especially coupled with modern air exchange systems, is extraordinarily complex. I doubt we can get a truly firm handle on this, but it is clear that the range of .70 to 1.00 as multiplying factors does not adequately express the difference between the situation with reasonably good climate control (whether building wide or with dampchaser systems) and what happens when there is no climate control. Anecdotally, at UNM the humidity stays mostly within the range of 20 - 30% during spring semester for the most part (with occasional spiking). A piano in reasonable tune at the beginning of the semester will generally stay within 5 cents (not counting the new, loaner pianos) throughout the semester. The humidity rises to 60 - 70% in the June to August period, so that at the beginning of fall semester all pianos are 25 - 45 cents sharp (requiring major pitch change, obviously). The humidity then begins to drop, and reaches 10 - 20% in late November to December. I tune the typical piano two additional times, each a major pitch raise of 15 - 30 cents. So in spring semester, with humidity stable, one tuning creates a better overall situation than three tunings fall semester with humidity swinging fairly dramatically. And those pianos in which I have installed humidistat and heating element are considerably more stable fall semester, but vary much more in fall than any piano spring semester. In other words, I think the humidity stability factor should be large enough to create a difference in multiplication factor of over 100%, rather than the current circa 50% difference. This being fudged with just how tight a range we are trying to keep the average piano in. But I doubt we can make this anywhere near an exact science, as the difference between the effect of a given humidity swing in an old building (heated, say, by radiators, like the small liberal arts college I attended 30 years ago in Ohio - humidity ranged from 20 - 90%, and the pianos weren't tuned more than once a semester, but they stayed reasonably close to pitch), and the same swing in a new building where the air is exchanged many times a day is just astounding. The latter systems create a constant (though not very noticeable) air movement, which magnifies the movement of moisture into and out of the saoundboard wood. Probably there should just be some verabl commentary to that effect, rather than an attempt to ascertain just how much of a difference these modern HVAC systems have made. Regards, Fred Sturm University of New Mexico
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