Day 18 with little change since yesterday. Humidity in case with 2 Dampit style humidifiers is at 44% RH for 3rd day in a row.  We're back in a cold spell, so we'll get another chance to see the effects of reduced humidity on the testing. Currently, ambient humidity is at 24%. 

Day 17 with little change since yesterday. Humidity in case with 2 Dampit style humidifiers is down 1% RH.

At 15 days into the testing, the 2 Dampit style humidifiers are down 5% RH from their high of 50% RH 8 days ago.

The Dampit type humidifiers are down by 4% RH from their high of 50% RH, so we may be seeing a decline in humidity already.  

It's a rainy, unseasonably warm day in Pennsylvania. Ambient humidity increased back into the 31% RH range. I keep tweaking the Musik Tent humidity toward 50% RH in the soundhole. Will likely leave as-is now.

Humidity in room is inching up as the outside temperature increases

Second update: Adjusted Musik Tent humidity up slightly this morning. Now reading 46% to 50% RH. Try that with a sponge humidifier.

First update: As expected, the humidity plunged to 20% RH with the outside temperature in the teens.

Essentially no change from yesterday. Cold front is expected to move in later today.

Here are current indoor humidity levels for the USA.

Below are some references for maintaining instruments at the proper humidity.

• Martin recommends 45% to 55% RH ( https://www.martinguitar.com/media/9615/2018-care-feeding-guide_web.pdf).
• Taylor prefers 47% RH (https://www.taylorguitars.com/support/maintenance/symptoms-dry-guitar)
• Guild recommends 45% to 55% RH (https://guildguitars.com/product-care/)
• Premier Guitars recommends 40% to 50% RH (https://www.premierguitar.com/articles/Fighting_the_Humidity_Battle)
• Fender recommends 40% to 50% (https://www.fmicassets.com/Damroot/Original/10002/2011%20Fender%20Acoustic%20Guitar%20Manual.pdf)

Ambient humidity increased 3% since yesterday, and is currently reading 29%. Case is reading 1% higher for all 4 probes (see summary table below) and continues to vary by 19% RH across the case. The testing is at 1 week since adding the initial dampit style humidifier. We're still expecting a sharp temperature drop in the next few days, with Monday's high expected to be around 15 Deg F. The heat will be running constantly, which should really drop the ambient humidity.

Dataset is starting to build, so I created a table to capture everything observed to date. Current conditions are 26% RH for ambient.  

In summary, the case humidity with 2 dampits continues to creep up with the soundhole now reading 49% RH. The overall variation from highest (soundhole) to lowest (headstock at 30% RH% reading is  19% RH.

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.