Humidity levels, inside and outside – the guitar... An interesting phenomenon.

Headless Folkie · #1 03-24-2024, 10:45 AM

So I've been aware of the concept of maintaining humidity levels for an acoustic guitar for a decade or so, and during the dry winter, I'm able to maintain humidity inside my guitar's hard case between 45 and 50%. (Originally with sponges in perforated soap dishes for the case, and a D'Addario -sponge- soundhole humidifier for the interior - and more recently, with water beads for the case.)

About a week ago, I bought an inexpensive Bluetooth hygrometer, so that I could check the humidity any time without opening the case, and when comparing it to my existing in-case hygrometer (both placed over the 'pick/capo/strings compartment'), they're within about one percent of each other. All good.

Then, out of curiosity, since I knew I could get a reading from the Bluetooth hygrometer through my tablet without having to physically see it, I tied a shoelace to it, and dropped it into the guitar body in the lower bout. Now to my surprise, while the case hygrometer is currently showing me 47%, the hygrometer inside the guitar body is reading 58% – with the case having been closed for the last couple of hours.

This roughly 10% spread has been consistent since I first tried this several days ago despite the fact that the soundhole isn't 'atmospherically sealed off' from the rest of the case. Granted, the soundhole humidifier will be dumping more humidity in the body than outside, but theoretically, the water beads are dumping more humidity outside the body than inside, and I would have expected an equilibrium to be established.

So, it would appear that all these years I've been humidifying my guitar past the ideal range. I'm not too concerned about it, as there are no physical signs of over-humidification (no bulging, no raised action, etc.), but it is an interesting little bit of information, and one that I suppose, will be changing my habits a bit when it comes to humidifying the case over the winter. Perhaps abandoning the soundhole-specific humidifier, and seeing then if the values inside the case and inside the guitar come together.

I'd be curious to see if anyone else has done 'inside/out' humidity comparisons while the guitar is in the case.

(And then, we'll see as the summer comes, what the two hygrometers show when I'm trying to DE-humidify.)

printer2 · #2 03-24-2024, 01:17 PM

I am assuming you had the two meters next to each other beforehand to compare how much they are out from each other. Yes you can have a localized increase in humidity, I would keep the water source outside the guitar.

Proclaimer888 · #3 03-24-2024, 02:20 PM

Thanks for the interesting post. I often wondered about the humidity inside the guitar.

warfrat73 · #4 03-24-2024, 03:14 PM

I guess that doesn't surprise me terribly, the unfinished wood that comprises the inside of the guitar body is dumping humidity into a somewhat closed box. The finished outer surfaces of the guitar are sealed (more or less). The soundhole is creating a bottleneck between the mixing of the outside-the-box air and the inside-the-box air. With time I suspect it will come back into equilibrium.

lar · #5 03-24-2024, 06:42 PM

This implies that a soundhole cover alone might be all that is needed (no case) - at least for the body. Not the neck.

mrghostwalker · #6 03-24-2024, 08:46 PM

I suspend my meter inside the sound hole. I figure the raw wood on the inside would give me a better reading level of the overall humidity.

JayBee1404 · #7 03-25-2024, 01:43 AM

Don’t over-think this RH thing. If your guitar lives in its case, and the overall RH within the case is generally in-range, i.e. low-40s to high-50s, IT’S FINE!

My advice is, spend less time examining the contents of your navel and more time playing the dang guitar!

As always, the standard disclaimer applies - IMHO. However, I realise that YMMV, and I’m cool with that.

BlueBowman · #8 03-25-2024, 03:52 AM

Quote:

Originally Posted by JayBee1404

Don’t over-think this RH thing. If your guitar lives in its case, and the overall RH within the case is generally in-range, i.e. low-40s to high-50s, IT’S FINE!

Yeeeessss! And I'll add even dipping below 40 now and again will not hurt a thing (at least IME).

Headless Folkie · #9 03-25-2024, 07:22 AM

printer2 - yes, they were side-by-side and within 1% of each other before 'separation.'

warfrat73 - agreed. It's one of those things that makes perfect sense when you think about it, but never really crossed my mind till now. Presumably, a guitar in a humidified ROOM, where the air is always moving about to some degree, will pretty much always be the same inside and out.

JayBee1404 - no fear. As noted, there are no signs of over-humidification (and the discovery didn't elicit a panicked removal of water beads or insertion of silica packs through the sound hole). As per the thread title, it mostly struck me as an interesting phenomenon and something to be aware of in the future.

Though, as the apartment humidity can dip to 25% in the winter, and even with a room humidifier running, rarely gets above 35% for those months, it IS something I do have to keep an eye on. Especially after the fate of my first guitar (fortunately much cheaper, but no less loved), which paid the price of my not being aware of such variables.

As for my navel, fresh lint is extracted on a daily basis. I'm thinking of making a sculpture of some sort. Perhaps a guitar...

printer2 · #10 03-25-2024, 08:09 AM

Quote:

Originally Posted by Headless Folkie

printer2 - yes, they were side-by-side and within 1% of each other before 'separation.'

warfrat73 - agreed. It's one of those things that makes perfect sense when you think about it, but never really crossed my mind till now. Presumably, a guitar in a humidified ROOM, where the air is always moving about to some degree, will pretty much always be the same inside and out.

JayBee1404 - no fear. As noted, there are no signs of over-humidification (and the discovery didn't elicit a panicked removal of water beads or insertion of silica packs through the sound hole). As per the thread title, it mostly struck me as an interesting phenomenon and something to be aware of in the future.

Though, as the apartment humidity can dip to 25% in the winter, and even with a room humidifier running, rarely gets above 35% for those months, it IS something I do have to keep an eye on. Especially after the fate of my first guitar (fortunately much cheaper, but no less loved), which paid the price of my not being aware of such variables.

As for my navel, fresh lint is extracted on a daily basis. I'm thinking of making a sculpture of some sort. Perhaps a guitar...

If you plan on making a guitar, head on over to the Build and Repair section.

Rjlipton · #11 03-25-2024, 02:50 PM

A while ago I got interested in how the water beads at the head of my case affected the humidity inside the guitar. I took two of the Govee sensors, one near the beads and the other inside the guitar body. The in-body sensor consistently reads about 10% lower than the case sensor. I then opened the case for some time to let the air mix with the room. I then closed the case and downloaded the humidity data after more than a day. The two track fairly well with the guitar 10% below the case. The fitted time constant for the guitar to equilibrate was about 2.8 hours and 1.8 hours for the case. Not profound, but kind of fun.