This thread seems to be heading in all sorts of directions. Heading back to low humidity, and what that does to tonal production, I have been puzzling recently over how to measure low humidities accurately. I have a sling psychrometer, but I have found that the lowest readings I can get with it are in the 18 - 20% range. I am thinking this is the limit of the particular instrument: that there is only so much evaporation that will take place from the wick, it only holds so much water, there are limits to how many calories that will be extracted to to the change of phase from liquid to vapor, something along those lines. It is bone dry here, no rain since November (well, we had a trace last night). My Air-guide hydro-thermo (similar to Radio Shack) has been reading 11 - 15% consistently as it sits in the music building. My Mannix (the grey one, about $80 from Pianotek, with a bulb on the top, that reads to tenths of percent/degree) has been down to 3% in one location, and under 10% consistently in many. Another indication is frost on the windshield. There hasn't been any, with overnight lows of 20F on average. Meaning dew point is below 20F. Pretty dry. Under those conditions, I thought the psychro would read lower, but no, 18%. So I'm wondering if anyone has thoughts about accurate measurement of humidity below 15%. I guess a dew point devise would work, where you lower the temp of a reflective surface (eg, polished stainless steel), and at the point where it begins to cloud over, that temp is the dew point (by definition). Not something I can make, and probably quite expensive to purchase. How do these electronic devises work? How accurate are they really? How much do they change in calibration over time? Regards, Fred Sturm University of New Mexico fssturm@unm.edu
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