In a previous life I was an engineer for the first generation of digital switches introduced into the public telephone system by the Bell System. These switches were extremely sensitive to environmental operating conditions. They generated quite a bit of heat and therefore require large amounts of A/C to keep the switch rooms down to an acceptable temperature, but as were added more A/C the humidity levels dropped to a point where the CMOS chips were starting to fail due to static discharges. We ended up in a number of installations having to run humidifiers in the same room as air conditioners to keep the humidity high enough to reduce static at the same time the A/C was dropping the temperature low enough to prevent overheating. This is a long way of getting around to saying that we too found that the ideal humidity level for operating this electronic equipment was 40-50%.
One interesting note is that too much humidity ended up being a bad thing also.When the humidity got much over 70% we started getting long term circuit board failures as some of the current flow cause enough of a magnetic field to attract dust to the PCB traces. When the humidity got high, the moisture in the air would react with this dust and form acidic compound which would "rot" the materials on the traces and cause premature failures.
So adding a little humidity to your mancave can be a good thing, just don't over do it or you could add up solving one problem and just creating a new one. (Besides, high humidity can make your records start to smell moldy.
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Now all of this has to do with protecting our equipment from failure (and of course broken equipment produces no sound, which is big time on the bad end of the spectrum), but does not address how the sound itself changes with respect to humidity. One summer I was working on the sound crew for a local outdoor concert series, and one of the artists performing that year was Peter Nero. He was playing a Steinway piano and since we were in the NY Metro area, Steinway sent one of their technicians over to tune it for him. I remember the technician being very concerned with the humidity level, not only the absolute level, but also how that level might have changed form 2 in the afternoon when he tuned it to 8 in the evening when the show would be starting. So if the humidity can effect the wood and the sound of a piano, I guess it could also effect our speaker enclosures and therefore how they sound.
I personally have never given any thought to, nor done any specific analysis of humidity vs sound quality issues. I think a lot of us just figure that when it gets humid, all of our neighbors turn on their A/C and screw up the power grid. But I have never given any thought to if there might be a direct link between humidity and sound over and above the derivative effect of noise on the electric service.
Does anyone else out there have any experience or thoughts on this aspect?
Tom