Acoustic guitars are made of wood, and wood shrinks as humidity in the air drops, and swells as it rises. So, why should you care? Because shrinking and swelling can cause permanent damage to your guitar. What’s the answer? A humidifier. Keep reading and I’ll explain the different types and how to choose a guitar humidifier.
As I said, the shrinking and swelling that results from changes in humidity can really do a number on a guitar that isn’t properly taken care of. Glue joints will fail. Cracks will develop in the wood. The guitar will lose tone and volume. You might even experience a discoloration in the finish. And the really bad news is that these types of repairs are expensive. Much more so than investing a small amount on a humidifier to prevent this damage.
When I first heard about using a humidifier, I doubted its usefulness. After all, the wood used in the construction of a guitar is not green; its already been dried before milling into the instrument in your hands. The problem is that these days, the wood used has been kiln-dried, then made into a guitar in a climate-controlled facility, then probably sold in a climate-controlled room. All of which serves to keep the moisture content in the wood relatively stable. Then you get it home, and the guitar is now at the mercy of the local climate.
Types Of Humidifiers
There are three types of humidifiers that can be used with an acoustic guitar: sound hole, guitar case, and room humidifiers. I’ll explain each of these below.
A sound hole humidifier either covers the sound hole or projects down into the cavity of the guitar to supply moisture. These are the most popular and come in three main forms.
- Cover – these are thin plastic covers that fit over the entire sound hole. They have an embedded sponge or similar material. They are easy to use, generally, so long as they are sized right for the type and size of guitar. One problem – it can trap moisture in the body and not provide much moisture for the neck.
- Tube – this is a tube that inserts way down in the body cavity, and can be very effective. One caution: don’t let the damp tube sit in contact with the wood – it can damage the wood that it contacts.
- Hanging Container – this consists of a container that hangs from the strings down into the cavity, and holds either a sponge that releases moisture or an absorbent chemical that regulates humidity (releasing moisture when the air is dry and absorbing moisture when humidity is high). Some of these are made of rigid plastic that tend to stretch the strings while inserted, which, over time can carve deeper notches in the nut and the saddle. Others are made of a pliable cloth material that don’t put much pressure on the strings.
A guitar case humidifier sits in the case and keeps the humidity of the entire case regulated. These are generally a sponge or an absorbent material, like clay, that you dampen and put into the case. The primary advantage these have over sound hole types is they are more effective at regulating moisture in the guitar neck. One note – hard cases are more effective at working with humidifiers than soft cases since hard cases are designed to be more impervious and so they hold moisture in more effectively.
It’s possible, and certainly reasonable, to combine a case humidifier with a sound hole humidifier. The advantage of this should be obvious – you can more easily regulate humidity levels for both the body and the neck. In fact, at least one system (reviewed here) includes both types for the express purpose of taking better care of the entire instrument.
A room humidifier is a device that pumps moisture into the air in order to regulate the humidity in an entire room. Some advertise “cool mist” or “warm mist” (which, in my opinion, doesn’t matter as much as other factors), some use an ultrasonic method to spray the mist into the air, while others include a UV lamp to help purify the water vapor to make them healthier to live with.
There are several precautions that need to be taken if using a room humidifier, but if done right, these are very effective regulators of humidity. First, you must ensure that the unit is adequately sized for the room. Trusting an under-sized unit is almost as bad as no humidifier at all. Second, get a monitor so you know what the levels in the room actually are. And don’t just go down to the local Walmart or Target and get your average room humidifier. These just emit water vapor into the air without giving you the ability to control the levels. Next, make sure the unit is spewing vapor directly on your guitar. Last, use distilled water, if possible, so as to prolong the life of the unit. If you can’t, try running a bottle of vinegar mixed with equal parts water through the unit monthly. This will descale the unit and help make it last longer.
Ideally, humidity should be in the range of 40-50%. For reference, levels in the home in winter can drop as low as 15%. Even with a humidifier built into the furnace, the levels will probably not reach the desired range.
Get a hygrometer. These devices measure humidity in the air and can be really helpful at letting you know the levels in your case or your room. I do recommend you get a digital one because the cheaper analog types (ones with a needle) can get bounced around pretty easily and lose calibration quickly. It’s not unusual for one to be as much as 15% off, which might mean the difference between slightly dry or so dry the wood cracks.
How Often Must One Be Rewetted
Sound hole and case humidifiers need to be rewetted periodically. Some people like to do it daily, which is overkill. Recommendations vary, but a good rule of thumb is to refresh the moisture every 5 to 7 days. This is where a good hygrometer comes in handy to know when the levels have dropped low enough to need refreshing.
When you refresh a sound hole or case unit, dampen it and don’t wet it. Excess moisture can be damaging to the wood. If it has a sponge, wring out all the excess moisture. Wipe down the entire unit after refreshing so there are no drops or wet spots before putting back into place.
Which Type To Use
When used properly, any of the three types can provide the necessary humidity regulation to protect your precious guitar. And all three have their advocates and detractors, but I suspect some of the detractors didn’t actually follow the directions.
Room humidifiers are most effective for players with collections or those who like to keep their instruments out all the time. A guitar hanging on the wall or sitting on a stand is great for spontaneous playing. I know from personal experience I play more often when I don’t have to pull my guitar out of its case. If you like to keep your guitars out, get a room humidifier. If not, get one of the other types and keep it in its case.
One last consideration – cost. Sound hole and case units range in price from $5 to $25. Room humidifiers can run up to $100-150. Decent hygrometers can be bought for $25-30.
Well, that’s the basics on humidifiers for acoustic guitars. If you have any comments, please leave them for me. I love comments.
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