Temperature and humidity are the two culprits which cause pianos to go out of tune.
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.
Harpsichord, virginals, fortepianos, and clavichords are even more susceptible to humidity changes than pianos because of their thin soundboards and their lack of a plate. (That's the big hunk of iron that keeps the soundboard from snapping under the combined tension of the strings.) Although pianos are just as vulnerable to daily humidity fluctuations, you will notice a pitch problems more acutely in your historical keyboards.
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.
Digital pianos and electronic keyboards never need tuning.
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!
Work on your piano should be done by someone who knows what he's doing!
A tuner is one who tunes only. He also may be qualified to do a few small repairs. He may have had formal classwork augmented by hands-on training under the supervision of an expert. Or, he may have read a book and/or take a correspondence course and have no supervised applied experience.
A tuner/technician is more highly trained and can regulate and voice as well as tune.
A tuner/technician who is a Registered Piano Technician [RPT] member of the Piano Technicians Guild is more experienced and skilled yet. He must pass twelve hours of rigorous applied testing and several written examinations. (An RPT was formerly called a Registered Tune-Technician, RTT.)
Approximately 10,000 people in the US claim to be piano tuners (at this writing). Of these, only 4000 are members of the Piano Technicians Guild, and approximately 2500 of these members are RPTs. (The remaining 1500 Guild members are at various stages in experience and training. Some are new to the craft and are at an apprentice level, while others are nearly prepared to the RPT exams.)
The approximate 8000 non-Guild members have varying degrees of expertise, training, and experience.
If you do not have someone to work on your piano, ask someone who actively plays piano to give you a referral. Students should ask their teachers, and teachers should ask their colleagues. Ask for references and call them. If you are not pleased with the work done for you, find someone else.
When you call for an appointment, expect to be asked for information:
You probably will have some questions, too:
Don't expect someone to be able to come to your home tomorrow to work on your piano. Most work several weeks in advance.
If you're a teacher and have an emergency repair, as before a recital, your tech will make every effort to bail you out, but routine service should be scheduled well in advance because it is not a crisis situation.
Be ready when your tech arrives:
When a tech tunes a piano which has not been serviced in some time (or which is quite out of tune), she does not do a tuning, per se. She does a pitch-raise, which brings all strings to approximately the same tension so she 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, particular 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 (at extra cost) to tune. Have your piano serviced regularly and take steps to avoid large changes in temperature and humidity to avoid this.
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.
In order for her to fix it, you need to be able to tell your tech what the problem is. Mostly this means knowing how to tell the tuner which note(s) in particular displease you.
Here are some examples. The lowest note on the keyboard is:
The Middle C is:
The A above Middle C is:
For a layperson, or even a teacher who doesn't have a complete table of cycles per second lying around (you don't??!), the best way to communicate with your tech is to count up from the bottom of the keyboard to describe the notes that are out of whack (don't forget to count the black ones); or to write the offending notes in staff notation.
copyright 1999, Martha Beth Lewis, Ph.D.
Contact me for reprint permission.