One of the most common questions that gets asked of a piano tuner-technician is, “Why does my piano go out of tune?”

Actually, a piano goes out of tune for a variety of reasons. In this article, we will look at five reasons why a piano goes out of tune.

1. Strings Stretching Under Tension

The first and perhaps most obvious reason why a piano goes out of tune is that the strings, although composed of steel, are highly elastic and stretch when placed under tension.

Each string (and there are on average about 230 of them) bears a load of between 150 and 200 pounds. When you place that much tension on a length of steel wire, it is going to stretch. This is just simple physics.

This string stretching takes place quite rapidly in new pianos and in instruments that have been recently restrung. This is why manufacturers recommend that new pianos be tuned at least four times in the first year of ownership.

Piano wire becomes more stable after that first year. It continues to stretch, of course, but at a slower rate. This is why even a piano that is rarely played should still be tuned at least once a year. When a piano is neglected for an extended period, the normal tension that is on the strings is allowed to dissipate. It is common for pianos that are neglected for several years to be half a note or more flat. It is not good for the load bearing structure of a piano to be allowed to go for extended periods with a significantly reduced load.

Even though string stretching is the reason many people think of first, with the exception of new and chronically neglected pianos, this is not the biggest contributor to a piano going out of tune.

2. Temperature and Humidity Changes

It may come as a surprise, but the biggest reason why most pianos go out of tune is changes in temperature and humidity. And of these two, changes in humidity is the bigger factor.

The influence of temperature is fairly self explanatory. Piano wire expands with heat and contracts with cold, which affects the tuning. Most homes do not see enough of a change in temperature to have any significant affect on the tuning. This is more of a concern in facilities that are unoccupied for extended periods, such as churches and other public places.

But what about fluctuations in humidity? How could this affect a piano’s tuning? Let’s consider for a moment some of the basic structural components of a piano.

If a piano consisted merely of a set of strings stretched between two points, with no soundboard to act as a sound transducer, the sound produced would be extremely soft and weak. Very early in the development of the piano, it was discovered that a plank of wood, when placed under tension, very effectively amplified the vibrations produced by the strings. This plank of wood is called the soundboard.

In a grand piano, the soundboard is glued at its outer edges to the inner rim of the piano. You are looking at the soundboard when you open the lid and look past the strings at the horizontal wooden board underneath. It may appear as though the soundboard is flat. However, in a healthy, structurally sound piano, there will be a slight crown to the soundboard, meaning that the center of the board will be raised slightly higher than the edges. This can be verified by crawling under the piano and stretching a length of string from one end of the soundboard to the other. In a healthy soundboard there will be a gap of about 1/8″ between the string and the soundboard at the center of the board.

The strings connect to the soundboard by means of a long, narrow strip of wood called the bridge. A crowned soundboard not only produces better sound reproduction through compression of the wood; it also helps to seat the strings firmly on the bridge, resulting in what we call “downbearing.”

What does all this have to do with humidity fluctuations causing a piano to go out of tune? It’s really quite simple.

All wood contains a certain amount of moisture. How much moisture a piece of wood can hold is determined by the moisture content of the air that surrounds it.

When the soundboard is dry and the air that surrounds it is moist, the soundboard takes in more moisture. This causes the soundboard to expand. But remember, the soundboard is firmly attached to the rim of the piano at its outer edges. This means that instead of expanding outward, the only direction it can expand is upward, increasing the crown. This causes the bridge to push harder on the strings, which adds tension to the strings, causing them to go sharp. This effect is more pronounced at the center of the soundboard where it is more flexible than at the edges where it is more rigid.

When the soundboard is moist and the air that surrounds it is dry, the soundboard releases moisture. This causes the soundboard to shrink, reducing the crown. Consequently, less pressure is exerted on the strings by the bridge, which removes tension from the strings, causing them to go flat. Again, this is more pronounced at the center of the soundboard.

Now if every note shifted equally when this happened, pitch would simply float up and down and the piano would stay in tune with itself. But as we have already noted, this is not what happens. The whole piano is thrown out of tune as the various sections of the piano shift, some more, some less.

This is why manufacturers recommend that their pianos be tuned at least twice a year after the first year of ownership. Of course, it would not be practical to have your piano tuned every time there is a slight change in relative humidity. Once in the Spring or Summer, and again in the Fall or Winter, is enough to compensate for the major seasonal humidity changes that take place in most of our North American climate zones.

3. Poor Tuning Technique

Again, this may come as a surprise, but the technique used by the person who tunes the piano has a huge influence on the stability of the tuning.

There are two things that a competent piano tuner-technician will do that significantly improves the stability of the tuning.

A. Setting the String

There are many segments to a piano string, and only one of these sections “speaks.” For example, there is the segment that goes from the tuning pin to the capo bar or agraffe (the front termination for the speaking segment). Then comes the speaking segment. After this there is the segment that passes across the bridge and through the bridge pins. And the segment that goes from the rear bridge pin to the aliquot bar. And finally there is the segment that goes from the aliquot bar to the hitch pin. (The exact number of string segments varies from one piano to the next, and from one section to another within the same piano.)

In order for the tuning to be stable, the tension in all of these various string segments must be equalized. However, friction at the various bearing points makes this difficult to accomplish. An inexperienced tuner may think he has left the string in tune. But if he or she did not adequately “set” the string using firm test blows, one or more sections will have a higher tension than the speaking section. This unevenness will work itself out after he leaves, causing the affected strings to go out of tune.

B. Setting the Pin

Although made of steel, tuning pins are actually quite flexible. There are two ways that this flexibility of the tuning pin can come back to bite an inexperienced tuner.

First, because the pin is held so tightly by the pinblock (the block of hardwood that the tuning pins are driven into), the upper, exposed portion of the pin will twist slightly before the lower portion actually turns in the pinblock. If this twist is not removed and the pin returned to its neutral position, it will slowly untwist itself, causing the string to go out of tune. Of course, this happens after you have written the check and the tuner has left!

And second, the upper, exposed portion of the tuning pin is long enough that it can be bent slightly fore or aft. It is very easy to manipulate the tuning lever in such a way as to bend the pin slightly forward or backward. Once again, if the pin is not returned to its neutral position, it will eventually return on its own, causing the string to go out of tune.

When it comes to tuning stability, competence is worth paying extra for.

4. Playing the Piano

That’s right. Normal use will cause a piano to go out of tune. In fact, the more a piano is played, and more specifically, the heavier it is played, the faster it will go out of tune.

It is not possible to perfectly equalize every segment of the string. Through the technique of setting the string with firm test blows (see reason #3 above), a piano tuner can prevent major short-term tuning changes. However, as the piano is played, and especially as it is played heavily, the tension between various string segments will shift, causing the piano to go out of tune.

Pianos that receive heavier than normal use may need to be tuned more frequently than twice a year.

5. Moving the Piano

Although a long distance move will often cause a piano to go out of tune, unless the piano was handled improperly or has underlying structural problems, it’s not the physical act of moving the piano that caused it to go out of tune. Instead, it’s the fact that the piano was moved from one climate zone to another. So what we’re really talking about once again is the influence of temperature and humidity on a piano. (See reason #2 above.)

When a piano is moved to a new climate zone, it is a good idea to wait 3 to 4 weeks before having the piano tuned in order to allow the piano to adjust to its new environment. Depending on the severity of the climate change, there may be other considerations, such as the need for a humidity control system, that your piano technician may bring to your attention.

Most pianos do not need to be tuned after they are moved across the room, or even across town. I am amused at how many calls I get from people who just moved their piano to a different room in their house, and they’re calling me because their piano suddenly needs to be tuned. Never mind the fact that it’s been 20 years since the piano was tuned. The reason it needs to be tuned is because it was moved!

If you are in the Inland Empire area of Southern California and are in need of piano service, I would love to hear from you! You can call me at (909) 824-2561, or you can follow this link to my website’s contact page.