A piano must be in tune. If it is not, the pianist cannot play with other instruments. Intervals are not consistent. Tone quality is dull. Performers with perfect pitch become irritable beyond reason.
Pianos do not go out of tune evenly throughout the compass but differentially. Thus a specific interval in one part of the keyboard may sound more or less out of tune than the same interval elsewhere. The middle register tends to go our tune more noticeably than the high and low registers. This is because the bridges of the middle register are in the center of the soundboard, over the crown, where the soundboard is thinnest and most flexible. (The edges of the soundboard are the most rigid.)
Piano manufacturers suggest tuning two to four times a year. For a teacher, two is certainly minimal, with three or four much better.
Tunings done in October/November and June/July tend not to hold as well as other times of year because these are times of seasonal change. If you have your instrument turned quarterly, pitch changes resulting from seasonal climate variations will be largely negated because the next tuning coincides with a major change in the weather. Your tech can suggest the optimal tuning frequency (and time of year) for your locale.
Why Pianos Go Out of Tune
Temperature and humidity are the two culprits which cause pianos to go out of tune.
Of the two, humidity is more crucial. One or two days’ extreme change in humidity can have a noticeable effect on your piano’s tuning. A rainy week can wreak havoc.
Pianos like a humidity range of 35-55%. Ideal humidity is 42%. Even temperate climates have a humidity variance of 15-85%! (100% humidity is fog. The air is “full” and cannot hold any more moisture.)
Why does humidity matter?
When humidity is high (60% or more), the soundboard swells as it absorbs moisture from the air. When the soundboard becomes larger, the strings are under greater tension. When strings are pulled tighter, their pitch increases.
Sticking keys, sluggish action, and rusting strings/tuning pins are other consequences of continued high humidity. Pianos are not happy in rainforests, on houseboats or in beach houses.
When humidity is low (34% or less), the soundboard contracts as moisture is given up to the air. String tension is lower, and the piano goes flat.
Other effects of low humidity include rattling (loose) keys, slipping tuning pins, and cracks in the soundboard. Pianos are not happy in the desert.
Humidity changes with the seasons. In the eastern part of the US and Midwest, humidity is low during the winter. Summer is the opposite. Unfortunately, these changes do not cancel each other out: drops during long winters (low humidity) are more than rises during short summers (high humidity). The net change is a drop in pitch. In most parts of the US, a piano left unserviced for many years’ experiences quite a noticeable drop in pitch.
Places where it is moist more than it is dry, such as the Pacific Northwest, Florida, and Hawaii, are locales where there is a net rise in pitch. Here in Hawaii the humidity level is higher than on the mainland resulting in a variety on unique problems. Rust being the most damaging and swollen action parts causing sluggish response on the part of the key stick movement.
Since pianos don’t like extremes of climate, if you live where it can be damp (many parts of the US), you probably should investigate a dehumidifier for your piano. If your area has year-’round low relative humidity, you may need a humidifier. Some areas of the country may need both! Consult your tech.
Place your piano away from sources of humidity: kitchen, bathroom, swimming pools.
Pianos like the same temperatures as humans: 68 degrees Fahrenheit is ideal.
Place your piano away from places where temperatures vary widely during a 24-hour period or where extremes of outside temperature occur: in front of (or below) windows, skylights or other sources of direct sunlight; by woodstoves or fireplaces; near air conditioning or heating vents; or against an outside wall.
Sometimes that’s not possible, but do the best you can!
When a tech tunes a piano which has not been serviced in some time (or which is quite out of tune), he does not do a tuning, per se. He does a pitch-raise, which brings all strings to approximately the same tension so he can tune one string without affecting the others. If only one string were brought to correct pitch, the unequal stress would cause other strings to go out of tune. Also, sudden tightening would of strings can cause breakage; particularly if the strings are rusty or have been under pitch (very loose tension) for a while. A pitch-raise takes approximately 30-60 minutes.
Your tech will do a pitch-raise as a preliminary to a true tuning when your piano is flat by more than two cycles per second [cps; also called a Hertz, Hz].
If the piano is extremely flat (two to five years between service), the tech may do a pitch-raise and then leave the piano to settle for several days before returning to tune. Have your piano serviced regularly and take steps to avoid large changes in temperature and humidity to avoid this.