The Importance of Exacting Moisture Measurement in Making Musical Instruments

Wood Is Instrumental

For centuries, wood has been used to make fine musical instruments. Nothing else matches wood for its sound and beauty. Wood is a living, breathing, organic material that maintains much of its character even after it has been cut, dried and fashioned into a musical instrument. Part of wood’s nature is that it always contains moisture, and it’s always exchanging moisture with its environment, giving and taking it as the environment changes. This makes moisture very important for building and owning musical instruments.

To understand how important moisture is to your instrument, first you need to understand how moisture is measured.

Relative Humidity

Relative humidity (RH) is a way of measuring moisture in the air, which you’re probably familiar with from the weather reports. It measures the amount of moisture in the air compared to the amount of moisture the air could hold at a given temperature.

Moisture Content

The moisture content (MC) of wood is the weight of the water in the wood compared to the dry weight of the wood. It’s expressed as a percent. As the temperature and humidity of the air changes, the MC of wood changes. As the air becomes more humid, wood absorbs moisture from the air. As the air gets drier, wood gives up moisture to the air. The equilibrium moisture content of wood (EMC) is the MC the wood will maintain at a given ambient temperature and humidity

Moisture and Making Musical Instruments

When wood absorbs moisture, it expands, and when it loses moisture it contracts. A musical instrument is made of many wood parts that must be made and assembled with high precision. To maintain that precision, expansion, and contraction must be held to a minimum during the building process. This means the MC of the wood must be tightly controlled.

The secret to controlling MC in the wood is controlling the RH in the air. The entire shop or factory must be controlled to an RH of close to 50% and a temperature close to 74 degrees Fahrenheit. These conditions have been found to be very close to what your instrument will experience in normal use for most of its life.

When wood is first cut, it’s too wet to be made into an instrument. It needs to be dried first in a process called seasoning or acclimation. To season the wood, it’s stored in the controlled shop environment of 50% RH and 74 degrees. Eventually, it will reach an EMC of 6% to 8%, and stabilize there.

This process can take anywhere from weeks to many months, depending on the individual piece of wood. During the process, the MC must be closely monitored. To accurately measure MC, most instrument builders use a high-quality wood moisture meter. The Orion® 930, 940, and 950 dual-depth pinless moisture meters are among the most accurate in the industry and feature on-site calibration – an industry first. Their pinless design will not damage the wood, unlike pin-style meters do. They can be set for deeper or shallower measurement depth, and for measuring different species, which makes them perfect for musical instrument builders.

Why RH Is Important to Your Instruments

Controlling moisture is one of the most important things you can do to care for your instrument. Keeping it in an environment that’s close to the one it was manufactured in will keep the wood’s MC around 6% to 8% – right where it should be. This ensures that the wood remains stable and that your instrument looks, plays and sounds the way it should.

Your instrument can withstand short term extremes of temperature and humidity, but most of the time it should be within the ideal range of 45-55% RH. The easiest way to protect it is to keep it in its case whenever you aren’t playing it. This will protect it while you’re outside in the weather or in unconditioned spaces. It’s even best to keep it in the case when you’re at home unless you carefully control the conditions there.

If you live in an area of low humidity, like high mountains or the desert southwest, you’ll need to be especially careful. The best way to protect your instrument in dry areas is to use a case humidifier. These are small, inexpensive packets of moist material that you put in your case. They slowly release moisture to help keep the humidity in the case at the correct level. Also, be sure to have a digital hygrometer in your case. A hygrometer measures the RH of the air. Make a habit of checking the hygrometer each time you open the case. A case humidifier is a good idea even if you don’t live in a dry area, but be careful not to over-humidify your instrument. Too much moisture can also be damaging.

If you can, keep conditions in your home as close to ideal as possible. Air conditioning keeps humidity down during hot, humid months. In the winter, when heating systems are on, consider using a home humidifier, either portable or centrally installed.

Watch carefully for signs of stress from moisture extremes on your instrument. Too much moisture will cause parts to expand. On a guitar, for example, the top will arch too much and raise the bridge. This raises the strings and makes the guitar hard to play. The guitar might begin to sound dull.

Too little moisture will cause parts to shrink and possibly crack. On a guitar, the bridge might move lower, causing the strings to contact the frets and cause “buzzing.” As the neck shrinks, the frets might start to extend out from the sides of the neck.

If you see any of these symptoms, immediately take steps to properly humidify your instrument and take it to an expert to have it checked out. If you catch it early enough, most humidity problems can be corrected before your instrument is permanently damaged.

Follow these tips to keep your instrument in top playing shape:

• Keep your instrument out of direct sunlight and away from extremes of temperature or humidity.
• Store your instrument in its case, even when it’s at home unless you’re carefully controlling the temperature and humidity in your home.
• Keep a humidifier in your instrument’s case in dry climates or whenever the air is dry.
• Keep a digital hygrometer in your instrument’s case and check it often for an RH reading between 45% and 55%.
• Keep constant tabs on your instrument by watching for signs of moisture that’s too high or too low.

Things to Remember

Wood always contains moisture. It’s important to maintain the right MC to keep your instrument in top shape.

The secret to controlling MC in wood is controlling the RH in the air. You can do this by taking simple precautions to protect your instrument from extremes of temperature and humidity.

Periodic measurement with an accurate wood moisture meter will alert you to moisture-related issues, allowing you to take steps and either eliminate or lessen moisture-related damage to your instrument or raw wood materials.

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Last updated on May 4th, 2021