Quote:
Originally Posted by Bernieman
What should I consider as ideal for guitars ? I was reading the other day that people at Santa Cruz Guitars would keep a 49% rate in the plant all the time I think...I was thinking 45 % to 55% would be okay, but as you say 35-45%, it makes me wonder if it isn't a bit too much humidity after all ?
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It isn't complicated.
The guitar was made at 49%. The ideal is to keep it at all times at a constant 49%. Catch is, this isn't practical for most guitar owners to keep their guitars at a single RH all of the time. That's where practicality enters into it.
As the ambient relative humidity drops, guitars - and other wooden objects - lose moisture and shrink. If the stresses in the wood due to shrinkage are sufficiently high, beyond the strength of the wood itself, the wood will crack to relieve the stresses. The exact amount of shrinkage that will cause a piece of wood to crack depends upon a variety of factors: at no one value will all pieces of wood crack. So, it is a game of chance: the lower the RH, the greater the shrinkage, the greater the chances of cracking. The further your instrument is below the 49% at which it was assembled, the greater the chances of it cracking.
So what is the minimum desired RH? That depends upon how much trouble/cost you want to go to to maintain the humidity, how much chance you are willing to take (i.e. how far you are willing to let the RH drop below the ideal) and the circumstances of your environment.
If you maintain your guitar at 49%, the chances of it cracking are very small. At 40% the chances of cracking are increased. At 35%, they chances are even higher. At 20%, and below, you can expect it to crack and are lucky if it does not. You chose the balance - for you - between probability of cracking and the amount of time, money and effort you want to put into maintaining the ideal RH.
At the other end of the spectrum, higher than the ideal humidity, unless you maintain your guitar at near 100% humidity for long periods of time, you aren't likely to see much permanent damage to the wood - mold and mildew are possible. There are, however, two undesirable consequences of higher humidity that are not damaging.
The first is that the instrument swells. As it does so, the top, in particular, arches more. As it does so, it takes the bridge and saddle with it, increasing the string height over the fingerboard. This makes the guitar physically difficult to play. Some counter this by using a lower saddle, particularly during higher humidity months (e.g. summer).
The second is that many report instruments to sound deadened at elevated humidity levels, like the guitar is stuffed with socks.
These two things, practically, govern the upper limit of RH that most are willing to stand: sound and playability. Again, that is at the discretion of the individual player. Many have found that above 55 or 60% these negative things begin to become noticeable.
In conclusion, many are comfortable in balancing the risks of cracking by keeping humidity levels above 35 to 40%. Many are willing to accept humidity levels of 55 to 60% before experiencing changes in tone or changes in playability.