Musik Tent at about 12 hours after setup, in the upper 30's when I checked this morning. So, I increased the amount of exposed filament about 1.5 hours ago and humidity has increased into the 40's. Will check after work and report. Target is between 45 and 50% RH. Photo on right (below) shows reading of 41% RH at top of the body near the strap button/output jack and 40% inside soundhole. Two additional probes at headstock and neck/body connection, also reading about 40%, so a reasonable comparison is made with the guitar case study.
The weather forecast is claiming next Monday's high will be a frigid 13 degrees. With the home heater working overtime, the humidity should drop considerably. This will give me a chance to see how these soundhole humidifiers work under pressure, and how such a humidity drop will effect the other areas inside the guitar case. Also, setting up a Musik Tent with a second guitar to see how these two methods compare in the same room.
Checked humidity levels the next day and results were essentially the same as the day before for two dampit style humidifiers in the soundhole. Probe 1 in headstock area read 29%, probe 2 near neck/body connection read 32%, and probe 4 on top of the body near the strap button/output jack read 31%. Probe 3, inside the soundhole, crept up slightly to 43% RH. Ambient room read 30%. Plan to leave these humidifiers in place to see how long they take to dry out.
I also checked hygrometer accuracy by performing a salt test on the probes, and found they're reading a few percent higher than the expected 75% RH. While I might get truer readings by subtracting these amounts from the readout - at least in the 75% range, it's not so clear how this offset scales to lower humidity levels since the relationship may not be linear. For the sake of this testing, and not to over complicate findings, I will report the same values as on the readouts, recognizing the actual values may be a bit lower.
Are case humidifiers good enough? I decided to find out for myself. Reluctantly, I drilled holes in one of my Taylor cases, so I could feed hygrometer leads inside with probes placed at various positions in the sound hole and around my guitar. The goal was to allow the case to close tightly, without pinching the leads or having the case cracked partially open.
I placed my 414CE, that I normally maintain at 45 to 50% relative humidity inside a Musik Tent, into the case and inserted a wetted, dampit style, humidifier inside the soundhole. Next, I placed hygrometer probes in the headstock area (1), near the neck/body (2), inside the soundhole (3), and on top of the body near the strap button/output jack(4). I placed a another probe outside as a reference. I then latched the case shut and left this setup to stabilize overnight.