Why Does a Piano Go Out of Tune?

Tuning of a Steinway on Stage for a concert

We get this question now and then.

A simular question is:

“How often does a piano need tuning?”

Another thing is that people often say:

“Oh but I hardly played on it this year. Does it really need tuning?”

Pianos are stringed instruments, and even though they can be protected by certain things like:

temperature-controlled rooms;

humidity-control environments;

or even just standing in a place away from any external elements, “wind, rain, sun, etc.”

They still go out-of-tune eventually.

And no … it’s not necessarily true that a piano that has been moved across the room, needs tuning.

Most pianos are relatively stable enough that you could move it around a bit without going out-of-tune. Although it is a good idea to have the piano tuned after moving it by truck to a new location.

Here is an excerpt from a really good piano technician and rebuilder, Arthur Reblitz, from his book:
Second Edition

Why Does a Piano Go Out of Tune?

As explained throughout this book, piano strings are under a great deal of tension that is supported by the frame, plate, pinblock, tuning pins, bridges, and soundboard. Anything that affects the position of any of these parts will cause a change in tension and make the piano go out of tune.

Humidity Changes. Although a soundboard has a coating of varnish or lacquer, moisture from the air can seep into and out of the wood, mainly through the end grain, causing the crown to increase and diminish. This is the most important factor that causes a good piano with tight tuning pins to go out of tune. A piano goes flat, particularly in the midrange, in the early winter when the dry heat of the furnace draws moisture out of the soundboard, diminishing the crown. It goes sharp again in the spring when you turn the furnace off for the season and moisture from rain enters the soundboard, increasing the crown. This seasonal pitch change is noticeably absent from a piano kept in a climate controlled (temperature and humidity controlled) environment.

When the midrange goes sharp, some people listen to octaves in the treble and bass, and think they are flat and try to adjust them accordingly. But what you should do in this situation is to lower the pitch of the midrange to A-440 where it belongs. Don’t raise the extremes above A-440 to compensate for the midrange going sharp.

Temperature Changes. Fluctuations in room temperature surrounding a piano cause less of a change in tuning than humidity changes do. However, direct sunlight or heat from stage lights is so intense that it can cause rapid changes in the tuning.

Stretching of the Strings. New music wire has a lot of elasticity, and it begins to stretch as soon as you pull it up to pitch. New strings stretch the most during their first few years in a piano. Because of this stretching, many new pianos sink a quarter step flat within a few months after each tuning, for the first two or three years. Then the stretching decreases, and the pitch remains stable for longer periods of time. Some piano makers and rebuilders stretch their new strings with a small roller immediately after pulling a piano up to pitch. This procedure helps, but if overdone it is harmful to the strings. The louder and more frequently you play a newly-strung piano, the faster the strings will stretch, and the sooner they will stabilize.

Slipping Tuning Pins. This factor doesn’t enter into the tuning of a good quality new piano, in which the pins should be so tight that the string tension doesn’t cause them to turn. In an older piano that has been exposed to regular seasonal humidity changes for many years, however, the pinblock loses its tight grip on the pins. When the pins get looser, string tension causes them to rotate slowly, over a period of months, allowing the pitch to go flat.

Playing. The louder and more often you play a piano, the faster it goes out of tune by a small amount. This is due to equalization of tension along the length of the strings. The better you “set the strings” during tuning, the less this happens.

Summary. Every piano is subject to one or more factors that will make it go out of tune, including humidity and temperature changes, stretching of the strings, slipping of the tuning pins, inadequate setting of the pins and strings by the tuner, and hard use. How often should you tune a piano? This depends upon its condition, the environment in which it is located, and the musical demands of the owner. A piano used mainly as a piece of furniture probably won’t “need” to be tuned more than once a year. A piano that is played used regularly and is in good condition might get by with being tuned twice a year, each time the seasonal humidity changes. A piano given a daily workout by a professional musician or serious student might need to be tuned monthly or even more frequently.
“A. Reblitz”
Picture of a grand piano, cut so you can see the inside
The above excerpt explains clearly how and when pianos go out-of-tune.
Another thing we didn’t mention, was, that if you regularly maintain your piano, with annual or bi-annual tunings, “or more frequently”, the better your piano will stay in-tune.
With a set time slot for the tuning. If your piano only tkes an hour to tune, the technician can focus on something else your piano might need:
some voicing, removing some old rust from the bass strings, improving the tone, or a bit of regulation, so it plays better.

Make sure to keep your piano happy through all the seasons.