The piano is an acoustic stringed instrument. It usually has 88 different notes, each having one, two, or three separate strings. These strings are set into motion by felt faced hammers hitting each string or set of strings whenever a key is depressed. Most other stringed instruments such as the guitar and violin have just a few single strings which are either plucked or bowed to produce their note choices. All stringed instruments have a delicate balance in their dimensions and adjustments, and their strings always cross a “harmonic” bridge which floats in a special position on the soundboard. Whenever these instruments are tuned, the tension on the strings is changed. As a result, the pressure distribution produced by these changes determines the pitch level and intonation of the instrument.
The piano is pitched and tuned by adjusting the tension of each individual string. This is done by tightening or loosening each one by means of turning the screw-like tuning pin to which it is attached. The total pressure of all the strings pulling together on the piano’s harp plate, at pitch level A=440, is circa 38,000 pounds. The corresponding bridge pressure at this pitch level is approximately 1,500 pounds. This “bridge pressure” presses downward through the harmonic bridges onto the soundboard and produces the tonal balance, or intonation, we commonly call “tuning.” It is critical to maintain this pressure balance throughout the life of the piano in order to preserve its tone and serviceability. Serious damage is done to the instrument whenever its tuning “pressure” is allowed to relax or change more than just slightly. Regular maintenance service and tuning is recommended at regular intervals, and should only be performed by a qualified piano technician.
The frequency of maintenance service and tuning depends on how the piano is being used and the atmospheric conditions in which it is kept. The more frequently a piano is used, and how often it is subjected to temperature and humidity changes, determine how fast the tonal balance changes and how often these services should take place. Even with no use at all, the piano requires service and tuning twice a year in order to preserve its pitch level, intonation and mechanical reliability. The tuning and general maintenance care of the piano instrument is a very important factor in its performance life and should be carefully considered with a piano dealer or qualified piano technician.