How Do Fluctuations In Humidity Make My Piano Go Out of Tune?

Relative humidity may be a bit of a dry topic, but it is a key to understanding how pianos react to their environment and how you can best maintain your piano.

Let’s define Relative Humidity. According to the Piano Technicians Guild, “Relative humidity (RH) is the amount of moisture contained in the air, compared to the maximum amount of moisture that the air is capable of holding.” That “maximum amount” of moisture that the air can hold is determined by the temperature. The warmer the air, the more moisture it can hold. Therefore, if you increase the temperature without adding any extra moisture, the relative humidity decreases. This is because the “carrying capacity” of the air has increased while the actual amount of moisture has remained the same. If you think that’s just a theory that doesn’t hold water, please read on to find out exactly how humidity can throw your piano out of tune!

Many important parts of the piano are made of wood, and wood is particularly sensitive to changes in relative humidity. At higher humidity, wood absorbs moisture from the air, causing it to swell up. This has big effects on the piano’s soundboard, often made of Sitka spruce, and the bridges, which are made of layered (laminated) beech or maple. The piano’s strings stretch over the bridge, which transmits their vibrations to the soundboard. The vibration of the soundboard transduces the strings’ vibrations into air pressure changes. In other words, the soundboard passes energy from the strings to the air so we can hear it.

Piano Bridge Less Crown

Two diagrams show a string stretching over the bridge, which is attached to the soundboard. The first shows a soundboard with less crown. The bridge does not press up into the string with as much force, which can lower the pitch of the string. This is what happens in dry environments at lower humidity levels. Image credit: Dampp-Chaser


Piano Bridge Increased Crown

Two diagrams show a string stretching over the bridge, which is attached to the soundboard. The second image shows a soundboard with an increased amount of crown. The bridge is pressing up into the string with more force, raising the pitch of the string. This is what happens at higher humidity levels. Image credit: Dampp-Chaser

The soundboard has a crowned or slightly arced shape, which pushes the bridge firmly against the strings. So, when humidity goes up, the soundboard swells up as the arc intensifies, and the amount of crown increases. This pushes the bridge more firmly against the strings, increasing the tension on the strings and making them go higher in pitch. In short, we expect the piano to drift sharp during the times of the year when it is more humid, and flat when it’s less humid. This effect is most pronounced in the middle of the piano’s range, where the soundboard’s crown is at its peak.

piano bridge pianos inside out

This image shows the piano’s steel strings crossing over the bridge. On the top of the bridge, the strings make their way through the bridge pins Image credit: Mario Igrec, Pianos Inside Out (In Tune Press, 2013)

At the other end of the strings, we tune the piano by turning the tuning pins, which control the tension of the strings. The strings are coiled around the tuning pins, which are driven into the pinblock, a multilayered wooden plank. Uncontrolled fluctuating humidity can also cause damage to the pinblock, which will have a negative effect on the piano’s tuning stability. This damage can include loosening of the tuning pin holes. The pinblock can crack and its layers can come apart (delaminate).


This image shows a tuning pin held in the pinblock in its proper position, slightly angled away from the string. Image credit: Dampp-Chaser



A damaged pinblock can allow the string to pull the tuning pin out of its proper position, and weaken the tight fit between the pin and the pinblock Image credit: Dampp-Chaser

Here’s what you can do to help fight the effects of fluctuating humidity and improve your piano’s tuning stability. First, get your piano tuned! It is recommended that pianos be tuned at least twice a year. Pianos need to be “trained” to stay in tune, especially when they are new– so having your piano        tuned regularly will help keep it stable. Second, position your piano away from heaters, air conditioners, windows, or any other location where it will be subject to environmental extremes.

Lastly, consider a humidity control system. The Piano Life Saver system from Dampp-Chaser can be installed in grands or uprights. It consists of a Humidistat, a Humidifier, and a Dehumidifier. The Humidistat constantly monitors the humidity level and activates the Humidifier or the Dehumidifier as necessary, in order to keep the relative humidity level inside the piano near the recommended 45%. This will make your piano’s tuning, regulation, and touch as stable as possible, allowing you to focus on making beautiful music.

Right now you can set up an appointment to install a humidity control system in your piano with one of our fine technicians. Book online today.

To find out more about humidity control, check out the piano lifesaver website:

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Filed under Learning about Pianos, Piano Maintenance, Piano Repair, Piano Tuning

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