24 hours after opening the case, the humidity in the soundhole has dropped from 39% to 32% RH. Not wanting to further stress my guitar, I moved it into a humidity cabinet. So, what have we learned? Summarized below are my observations of humidity when 2 wetted dampit style humidifiers are inserted into the soundhole of an already humidified guitar, inside a top quality case:
Humidity in soundhole took 6 days to reach 50% RH.
The maximum humidity variation inside the case was 20% RH, from soundhole at 48% RH to headstock at 28%. Note, this was on a day with one of the lowest recorded ambient humidity of 19% RH.
The maximum humidity variation between the soundhole and ambient humidity was 29% RH, also on same day ambient humidity was at 19% RH.
Soundhole humidity never exceeded 50% RH, and tended to decrease about 1% RH every few days (2 days at 50% RH, 3 days at 48% RH, 2 days at 47% RH) until bottoming out around 41% RH.
2 wetted dampit style humidifiers lasted about 3 weeks or so before drying out. Afterwards, with the case remaining closed, the decline in humidity inside the soundhole was about 1% RH every 4 days or so.
Swings in ambient humidity from a low of 17% RH to as high as 35% seem to have minimal effect on the test results
Here are my observation of the Musik Tent for comparison:
Humidity in soundhole took about 2 days to reach 46% RH. Later, I increased the filament setting to get closer to 50% RH.
The maximum humidity variation inside the Musik Tent was 4% RH.
The maximum humidity variation between the soundhole and ambient humidity was 30% RH, on the day with the lowest recorded ambient humidity at 17% RH.
Soundhole humidity never exceeded 51% RH, and tended to swing 1 to 2% RH with ambient humidity.
3 cups of distilled water lasted during the 26 days of testing, and the remaining amount is estimated to last at least another 5 months or so, depending on ambient conditions.