60% constant relative humidity

[RodB]

Originally Posted by iim7V7IM7

....You need to consider the temperature (as well as elevation/barometric pressure).

I would suggest that for our purposes it is not necessary to consider these.

The expansion / contraction in the wood of our guitars is as a result of changes in it's Equilibrium Moisture Content (EMC) not the moisture content in air. The main contributor to this is Relative Humidity. Whilst there is a small temperature effect this is not significant in the range of temperatures to which we would expose our guitars. The Hailwood-Horrobin equation actually demonstrates this.

[charles Tauber]

Originally Posted by iim7V7IM7

We'll just have to disagree on this one.

I'm okay with that.

The equalibrium moisture content (EMC) of the bound and free water in wood is based upon...

In dried lumber, free water content is irrelevant is it not?

[geordie]

hovering around 90% here on the west coast o' Scotland cloud base is <> 300ft - I'm in the clouds

[iim7V7IM7]

Originally Posted by charles Tauber

I'm okay with that.



In dried lumber, free water content is irrelevant is it not?

Agreed, in dried lumber ~6-8% is mostly bound water. It does not change my point.


Temperature by month in NYC:



Relative Humidity by Month in NYC:



Why is it dryer in the winter in my house when outside we have 45-90%RH? Why do guitars crack and dry out? Its plenty moist isn't it? The colder air at 60% RH holds very little moisture and the equilibrium in the wood was established at a higher temperature and therefore a higher atmospheric molar concentration.

This was the point that I was illustrating in my earlier post. Air in the mid 80s F holds 2x the moisture of air in the 60s F. Moisture will move in and out of the wood at a different flux based on the molar concentration in the atmosphere and not "%RH".

Glad we're still friends though!

[Diamond Dave]

I'm going to answer this question definitively, so everyone pay attention. The answer is:

It depends.

If the humidity is making your guitar do funky things, like raising the action on the one extreme or cracking on the other, then it's a problem.

Every guitar is unique. Keep an eye on your guitar and take the appropriate measures.