Ideal temperature and humidity for acoustic guitars

[devellis]

Back when I was interested in older mandolins (like pre-WWI old), I did some research. The most credible sources I found were museum preservationists. These were people with advanced degrees focusing on preserving, maintaining, and restoring very valuable artifacts. There was strong consensus that the ideal RH for wooden objects, including instruments, was 45%, with 35-55% being a completely acceptable range. As best as I could tell, that range was symmetrical, with 35% being just as instrument-friendly as 55%, a view that doesn't seem to have found its way into guitar lore where dryness is always seen as worse than moistness. (I think manufacturers are especially concerned with top cracks from excessive dryness, so they prefer that owners avoid low RH, perhaps exaggerating the point at which RH is dangerously low as an extra measure of safety.)

Temperatures, as I recall, were less critical and I think the assumption was that they would be in the range of comfortable indoor temps, perhaps 65 to 75 degrees or so. Temperature impacts humidity. In the controlled environment of a museum, each is regulated independently, so, as temperature goes up, RH doesn't go down because it is actively maintained within a target range. At home, this won't generally be the case. So, a hot room in your house will likely have lower RH than a cold room in your house, as the air's capacity to hold moisture increases with temperature. But if RH is kept constant, I think the safe temperature range is actually pretty wide, more so than the safe RH range.

We all know the problems of low humidity. Wood dries and can crack. While it may be true to a degree that wood maintained at a lower humidity "adapts" to it and becomes stable, that isn't an absolute by any means. A well-known incident in museum circles is the time that night watchmen at the Isabella Stuart Gardner Museum in Boston heard what they thought was a rifle shot. They looked around and didn't see anyone who could have fired a rifle. When the museum staff returned in the morning, they found that a centuries-old wooden artifact had split in two as a result of the dryness of the air in the museum. The sudden failure of the wood on this hefty wooden sculpture was the "rifle shot" the guards had heard. (As an aside, this same museum was the location of one of the largest unsolved art thefts in modern museum history, with the proceeds of sales of the art allegedly going to support IRA activities in Norther Ireland during the time of the unrest in that part of the world. It's a very nice museum but it's had its share of bad luck.)

High humidity can do bad things, too. Metal parts can rust, wood can swell, adhesives can soften, and mold spores can germinate. Wood swelling and adhesives softening can be especially harmful. But even if adhesives hold, swelling wood creates stresses that may manifest in harmful ways other than a failed glue joint. So, don't assume the only down-side of too much moisture is dulling your guitar's sound.

Brief excursions outside the ideal RH range are pretty unlikely to cause any dire problems. But chronic exposure to humidity extremes in either direction can lead to trouble.

[vindibona1]

Originally Posted by fazool

Both Martin and Taylor recommend 45%-55% as ideal RH.
Personally, I prefer 40% as my target.

I too shoot for 40%. It it starts getting more humid than that the guitars start to sound like someone's thrown a blanket over them. Mine sound best between 35%-40% but if the room goes up to 45% I don't fight it. Over 45% the humidifiers get turned off.

[nitram]

Just for interest's sake the Louvre maintains the Mona Lisa @ 47.6 %RH and 19C. It was painted on a slab of poplar and isn't a musical instrument, obviously,but that's what they feel is optimum.

[Ricky Nelson]

I'm pretty new. Good post.

I gotta ask though, if its high humidity do you just not play out? I'm in New England and we get some extremes. I pay just a little attention.

I've been careless about humidity and better about temperature change. Is it really that much of a risk? My Gibson has put up with my abuse, but I'm thinking about an expensive upgrade. Is it that dangerous? If yes, maybe I should stick with my road proven Gibson and my Martin beater and abuse them to my amusement? Stay away from pricey precision instruments?

Thanks
RNF

[1neeto]

I live in Hawaii so humidity here is constantly high. Guitars inside cases seem to be fine with me throwing a few of those silica packs. I should throw a hygrometer in there to be sure.

[Gasworker]

Well there you go. Let us know which guess you're going with

[Earl49]

If your guitar sees 39% RH for more than seven minutes, it will implode in a dramatic, catastrophic failure. If it sees 61% humidity for a half hour, it will sound like it is full of wet laundry and will never be worth playing again.
Just kidding! I exaggerate for effect.........

Attention to humidity care is certainly worthwhile, but don't make yourself crazy obsessing about it. Extreme and prolonged dry conditions can cause wood to shrink and crack (most often at the center seam of the top). Extreme wet conditions cause wood swelling, usually with accompanying high action. Rapid or extreme changes are worse than long term exposure to dry or wet conditions. Changes happen in hours or days, not minutes or seconds. These wooden boxes are more durable than you might gather from the online chatter.

[Theleman]

I have seen buskers on rainy days not in the open street at their usual spots, but escaped into indoor market alleyways, and playing acoustic guitar there. It still must be very humid, because it was pouring down with rain, windy and freezing cold outside.

Definitely better with all laminated acoustic in this situation, I would imagine

[1neeto]

Originally Posted by Theleman

I have seen buskers on rainy days not in the open street at their usual spots, but escaped into indoor market alleyways, and playing acoustic guitar there. It still must be very humid, because it was pouring down with rain, windy and freezing cold outside.



Definitely better with all laminated acoustic in this situation, I would imagine

Yeah I would think that laminated woods won’t absorb as much water. But then again I’ve seen my laminated guitar with the a swollen back sometimes.

[Theleman]

Originally Posted by 1neeto

Yeah I would think that laminated woods won’t absorb as much water. But then again I’ve seen my laminated guitar with the a swollen back sometimes.

Maybe because they tend to be neglected?

[1neeto]

Originally Posted by Theleman

Maybe because they tend to be neglected?

I play that guitar quite often since it has a lovely neck. It usually swells if I leave it on a stand for a few days. Once I put it back in the case it goes back to normal.

[Theleman]

Originally Posted by 1neeto

I play that guitar quite often since it has a lovely neck. It usually swells if I leave it on a stand for a few days. Once I put it back in the case it goes back to normal.

Does it go back to flat from the swell afterwards when placed in the dry?

[Gasworker]

Originally Posted by 1neeto

I play that guitar quite often since it has a lovely neck. It usually swells if I leave it on a stand for a few days. Once I put it back in the case it goes back to normal.

Does the swelling affect the fret board at all?

[1neeto]

Originally Posted by Gasworker

Does the swelling affect the fret board at all?

Other than the guitar going sharp, it doesn’t really affect its playability.

[1neeto]

Originally Posted by Theleman

Does it go back to flat from the swell afterwards when placed in the dry?

Yeah the tuning fluctuates. Less humidity, it goes flat, high humidity it goes sharp. I’d imagine a solid wood guitar would fluctuate even more.