Piano tuning is the adjustment of string tension, not to specific pitches, but to the point where the piano has the most even, balanced, and musically pleasing sound.
When a piano is tuned to standard pitch the combined tension of the 220 to 240 strings is up to 40,000 lbs. Due to this tension there is a downward force on the soundboard through the bridges of up to 1000 lbs. Though it appears flat the soundboard is arched or “crowned”. Therefore, there is an upward force in opposition to the load of the strings. Because of this, fine tuning can only be achieved when a piano is close to its final tension. If a piano is not close enough to pitch, some or the entire piano may need a course tuning before fine tuning is possible. It is therefore, important to keep a piano as close to in tune as possible.
Though a piano has a cast iron frame or “plate’’, it is largely a wooden structure. As with all wooden things, such as drawers and doors, pianos are subject to expansion and contraction due to humidity changes. The soundboard in a piano is glued to the rim around its perimeter. When the soundboard takes on moisture due high humidity it cannot go out as it expands. Therefore, the crown is increased which in turn pulls the strings tighter making the pitch go sharp. Conversely, as humidity drops pitch is lower. No two pianos are the same as no two pieces of wood are the same. Some pianos are more sensitive to changes in humidity and may require more frequent tuning. Any piano will benefit by being in an environment where changes in humidity are controlled as much as possible. In northeast Ohio, with very dry winters and very humid summers, it is a challenge to maintain a reasonably constant humidity level for a piano. Sometimes humidity control can be added to the piano to help mitigate the effects of an unstable environment.
Only an experienced and well qualified Cleveland piano technician can determine the tuning schedule that best fits your piano.