What is Relative Humidity and Why is it Important?
Why is relative humidity so important to maintain if you want your acoustic guitar to live forever? Well, in more humid environments wood will gain moisture, causing it to expand; in less humid environments, wood will lose moisture, causing it to shrink. The average guitar is built in factories that maintain a relative humidity of around 40-45% in 22 degree Celsius. Because of this, we want to maintain an environment to store our guitar in that has this relative humidity.
The reason humidity is relative is because at higher temperatures air holds more water than it does at lower temperatures. This means that if our house is 30 degrees, like it may be in the peak of summer, there is more water in the air than there would be in the middle of winter when our house is around 16 degrees. In both times of year our hydrometer (device that measures humidity) might show the same reading of 45% or so. Just remember that the relative humidity that we want to maintain for our guitars is 40-45% at 22 degrees Celsius, which is considered room temperature. If the temperature drops, our humidity readings need to be higher. If the temperature rises, our humidity readings can safely lower.
Most guitars can handle relative humidity drops of 0-5% below the level at which it was built, and increases of around 0-15% above. Anything prolonged exposure to environments outside of these boundaries will result in damage, and if the exposure is for too long, the damage can be irreversible.
Watch for these signs in the summer time that will suggest over humidification of your instrument:
- The back and top of the guitar will swell up and become more convex than usual.
- As the top of the guitar swells and rises, the bridge is pushed high causing a rise in the action.
- Glue joints of the guitar will be more noticeable. Inlays will have spaces around them, especially ones that aren’t made of wood. For example, pearl inlays will not expand with the introduction of high humidity, but the wood surrounding the inlays will.
- As the finger board expands around the metal frets, they can also become loose which results in the next bowing more than usual. This will also contribute to a higher action.
- If your guitar has a finish, it will sink into the pores of the wood as it expands leaving the guitar with a corrugated or rippled look.
- You may notice tarnish or discolouration on metal hardware.
- Most importantly, after all the changes your guitar may go through, the sound will also change. Subtle changes will cause subtle changes in sound. But serious changes will make your guitar sound like a cheap Yamaha or Fender.
Luckily, if you notice these changes taking place soon enough, they are generally reversible by simply returning the instrument to a suitable humidity. You can avoid these problems all around by using a dehumidifier to control the humidity in your music room. It’s also a good idea to keep your guitar out of the case during high humidity times of year so the air can circulate around it. Do not leave it in dark lower levels of your house such as a basement where humidity and moisture easily builds up and settles.
Watch for these signs of dehydration during colder times of the year:
-The most obvious evidence of dehydration is sharp frets. As the wood finger board shrinks, the metal frets do not. The ends of the frets then stick out beyond the finger board. This is usually noticeable before anything because you can feel them nearly cutting your hand when you play.
- The top of the guitar will start to shrink in, looking concaved. When this happens the thicker less vulnerable bridge will not shrink as fast. This will appear like the bridge is lifting off the top, but it’s usually actually the top dipping away from the bridge.
- As the bridge lowers with the sound board, the action lowers which causing the next to bend back more. This can cause buzzing. You may also notice the appearance of the neck dipping into the sound hole as the top sinks in.
- Lastly, you may notice cracks in the more fragile parts of the guitar.
The problems associated with exposure to low humidity are more serious than the problems caused by over-hydration. Most of these issues are not reversible - especially cracks. During colder times of the year it is a good idea to invest in a humidifier to keep your music room in good shape. It is also a good idea to leave your guitar in the case during this time of the year. I have heard of some people actually bringing their guitar into the bathroom and leaving it on a stand while they have a hot shower upon discovering the first signs of dehydration. I have not done this myself. I would only experiment with this on a cheaper instrument to see the results.
Just remember that your guitar will not take care of itself. Just like a pet, it will die and serve no purpose if you neglect it. There are many types of guitar humidifiers available at Simply Music to help maintain the proper relative humidity for your instrument, as well as hydrometers that will let you know what the levels are currently sitting at. Most guitar manufacturers will let you know what they recommend you keep their guitars in when you purchase one. Take this advice seriously, and remember, if you ever have any questions, Ben at Simply Music is an expert with this topic.
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