Tom DeFerrari Piano Tuning and Servicing: Why a Piano Goes out of Tune

Tom DeFerrari Piano Tuning and Servicing

Why a piano goes out of tune

.Four reasons why a piano goes out of tune

1. Changes in humidity

The strings on a piano are stretched across a cast iron plate, and press against bridges that sit on top of the soundboard. The soundboard is a 3/8 " thick spruce board that sits below the strings and goes the width and length of the piano, not counting the keyboard area. It is the wood that can be seen just under the strings when looking inside the lid of a grand piano. The vibrations of the strings are transmitted through the bridges to the soundboard, which then amplifies the sound. This setup is much like the top of a guitar, or better, a violin, since the soundboard has a curvature or crown, so that it is higher in the center than at the edges. In addition, the piano bridges are much thicker, to handle the large downward pressure of the piano strings.
When the soundboard absorbs moisture due to high humidity in the room, it swells and presses upward against the strings through the bridges. This causes the strings' tension to increase, which causes their pitch to become sharper. Since it presses against the different strings in different degrees (more along the center, less along the edges) the strings don't go sharp equally, and the result is an out of tune piano. Conversely, when the soundboard loses moisture due to dryness in the room, the soundboard contracts and the strings slacken and become flatter, with the same result, an out of tune piano.

This diagram is of a grand piano taken apart. The cast iron plate is painted with a bronze paint, but is cast iron inside. The pinblock is shown without tuning pins or strings attached. It fits under the plate, and would have tuning pins driven into it, through the plate. Strings are attached to the tuning pins. This can be seen in the photo above. A vertical piano is very similar, except everything is in a vertical orientation.

2. Loose tuning pins.

The tuning pins hold one end of each string and are what the piano tuner uses to tune the piano, tightening and loosening each string to make it sharper or flatter, as needed. These pins are driven into a pinblock, which is typically a multilaminate plank of hardwood. When the piano is new these pins are very tight, and stay in place in the pinblock after a tuning. After many years, or sooner if the piano is kept in an overly dry room, the pinblock dries out and the tuning pins are no longer tight. At this point, the piano will go out of tune soon, if not immediately, after a tuning. Typically, a pinblock will last for 40 years or more, if the piano is kept in a stable and not too dry climate.

Options for correcting loose tuning pins

New Pinblock When the pins do become loose in the pinblock, the only failsafe repair is to replace the pinblock. This is a large rebuilding job requiring all the strings to be removed and the cast iron plate to be removed in order for the rebuilder to access to the old pinblock. After it is replaced, the plate (which is usually rebronzed) is reinstalled, and new strings are put on the piano. This should then last for another 40 years or so. This is a shop job, and the entire piano must be away for several weeks.

Tapping in tunings pins This often can make the pins tighter by driving them down into new wood in the pinblock. This is only a temporary cure, and can only be done once or twice, since eventually the string coils that go around the tuning pins would rub against the cast iron plate. In a grand piano, the keyboard must first be removed so that the piano technician can support the pinblock before tapping the pins in.

Repin old pinblock A repair that is sometimes possible is to replace the tuning pins with larger pins. If all goes well, these new tuning pins can last 20 years or so. It isn't always possible, though, especially if the pinblock is so dried out that the new pins would soon slip themselves. If the pinblock is cracked, or cracks during the repinning process, the new pins will begin to slip immediately. The procedure that I use to see if repinning is an option is to replace a few of the loosest tuning pins and see how tight they feel immediately after installation (they should be very tight) and how they hold up in the driest part of the coming year. If they feel at all loose at this point, a repinning would probably be a waste of money. This is a job that can be done in the home, and takes about 2 days.

Treating the pinblockThe third option is treating the pinblock with pinblock restoring fluid, sometimes called doping the block. In this case the piano technician pours a fluid into the pinblock that causes the wood to absorb more moisture than it normally would. This causes the pinblock to swell, and the pins become tighter, and with luck, tight enough to tune. It usually doesn't last longer than 5-10 years, and often it is impossible to repin with larger pins afterwards, since the wood of the pinblock becomes spongy. For these reasons it is somewhat controversial among some piano tuners and technicians. However, in some instances it makes sense. One is if the piano really isn't worth expense of a new pinblock or even repinning. The other instance is when the piano is of high enough quality that it would be worth installing a new pinblock at some point. In this case, treating the pinblock can buy the owner a few years before having a major job like a new pinblock performed.

3. Piano hasn't been tuned in years

When a piano hasn't been tuned in several years, the first tuning is usually unstable. The reason for this is that when a piano sits for years without being tuned, it will usually become very flat in pitch due to the strings losing tension. It's common with a piano that hasn't been tuned in years for each key to be one half note flat, and in extreme cases, each key might be more than two notes flat.When it finally is tuned, the tuner must add a lot of tension to each of the strings in order to get the piano back up to the standard pitch, which is called raising the pitch. The strings will then tend to stretch and go flat again, and in addition, the soundboard and bridges will respond to the extra tension by pushing back, over a period of time, until the piano is back in equilibrium. Anyone who plays a guitar will be familiar with this. If the guitar is taken out of the closet after not having been played in years, the owner will need to tune it several times before the tuning becomes stable. A piano, which has about 250 strings, each of which has about 160 pounds of tension on it, has altogether about 20 tons of tension across the cast iron plate. It takes time for this tension to redistribute itself when it is increased significantly, which happens after a large pitch raise.

4. New Strings

New strings will go out of tune very quickly as they stretch. A new piano is tuned several times in the first months after it is made until it becomes stable. Most manufacturers don't send the pianos out of the factory until they have become stable, but even so, a new piano in an owner's home will hold better after a couple of years of use (though only if it is tuned regularly in that time). In addition, a piano that has been restrung will have the same issues. If the piano was restrung in a shop, the rebuilder will do as the manufacturer does and tune it several time until it becomes stable before returning it to the owner. But again, like a new piano, it will hold its tune better after a couple of years of use.

If an individual string breaks and is replaced on a piano, it will also go out of tune very quickly. This is much more noticeable than when all of the strings of a new or newly restrung piano go out of tune, since they do so (to some degree) together. When the individual new string goes out of tune, it will sound radically out of tune due to being so far flat compared to the rest of the piano.