Real-Life Communication -- Solution
Paul Brown, registered piano technician, answers these common questions this way:
Music wire is spring steel. The best way to explain this is to use an analogy of a spring coil. When you pull the two ends apart, and then let them go, the spring coil returns to its original shape because it has been in that position for a long time. But if you stretch the ends too far apart, the spring coil will not return to its original shape and will likely stay in the new position.
Let's say that we have a coil that is six inches long that should be twice that length, or one foot long from bottom to top. If we want it to stay one foot long, we will have to stretch it considerably so it will stay that new length. Similarly, if we have a coil that is two feet long, we will have to compress it so that it will remain at its new one-foot length after we let go. In this example, we have adjusted two coils, one upward and one downward.
Even though now we are satisfied that these two coils are each one foot long, they probably won't stay that way. After they're adjusted, the coils still may change slightly. If we return in a couple of hours, the coils won't be exactly one foot long, because they haven't completely adjusted to their new position. It may take a day or a week for that to happen.
Just imagine how difficult it is for a piano tuner to adjust over 200 wires! If the piano hasn't been tuned frequently enough, a technician could spend all day tuning and the piano will still go out of tune, because the wires have not had time to settle into their new positions.
Humidity refers to the amount of moisture in the air. Humidity plays a major role in why pianos go out of tune. This is because humidity affects wood, and pianos are made of wood. Seasonal and even daily changes in humidity cause wood parts to swell and shrink, affecting tuning stability and touch.
One of these critical wooden parts is called the "soundboard." The soundboard is a sheet of wood about three-eighths of an inch thick, and has a slightly crowned shape. You can picture the soundboard as a thin membrane that vibrates up and down when it receives sound waves.
The piano wires, or "strings," pass over the soundboard and are connected to it by another wooden piece called a bridge. The bridge in a piano is analogous to that of a violin. The rounded shape of the soundboard presses the bridge tightly against the strings.
When there is very little humidity, the soundboard is fairly flat and the strings that are connected to them are at a certain tension. When the humidity is very high, the soundboard may warp. This expansion pushes the bridge harder against the strings. The strings are stretched tighter and the piano's pitch rises.
Since the wires have now been stretched, they are no longer at their original position and the piano goes out of tune.
If you have had the piano tuned on a day of high humidity, and the climate becomes much drier, the soundboard will flatten out and the wires will be "relaxed." In this case, they will no longer be at the position they were in high humidity, and the piano will be out of tune.
Even when the relative humidity returns to its previous level, the average pitch of all the strings will return to normal, although the exact pitch of individual strings will be slightly changed from their original settings.
Thus, a piano only will stay in tune as long as the humidity level in the air surrounding the soundboard remains constant.
This is why tuners recommend that pianos be tuned at the same time of year every year. This way, the tuner is likely to have the same weather conditions as they did when the tuning was done the year before.