Think of the sound-producing portion of the piano as being like a drum.  There is a wooden frame with an iron support (plate) to which two hundred and thirty or so strings are attached under tension.  When the total tension of all the strings is added together, the frame must hold exactly in balance from eighteen to twenty tons of pressure. The ability of the piano to have power and full tone requires the piano to be in a constant balance of tension and compression.  Like a drum, some parts must remain stationary while other parts are free to vibrate.  In a piano the soundboard must be free to vibrate while the plate and frame must be stationary.

The very nature of wood, which gives it resonance and strength, also makes it very sensitive to atmospheric fluctuations.  Wood is hygroscopic, meaning it takes in or gives off moisture from the air.  When humidity rises wood swells and when humidity lowers, wood shrinks.

Since piano strings and the cast iron plate are not affected by humidity these changes cause continual variations between wooden parts and metal parts.  The balance of tension and compression is constantly changing causing the tuning of the piano to fluctuate as humidity changes.  Any person living here in the Midwest knows our weather can change at the drop of a hat. Thirty degree temperature changes and twenty to thirty percent humidity changes in 24 hours are common.  This creates a difficult environment for keeping your piano in tune.  The more stable the surroundings, the more stable your piano will be.  The finest and the poorest instruments alike are affected by humidity.

Temperature changes also affect your piano and how well it remains in tune. It is advisable to keep the humidity and temperature as stable as possible in order to get the best performance from your piano. 45% humidity at 70 degrees is ideal. Orchestras and pipe organ companies suggest similar standards

A piano is both a work of art and a highly refined machine.  To keep your piano in  optimum condition requires regular service and a good environment.  When a piano is new there is a settling process that takes place over several years as the piano acclimates to its surroundings.  As new piano wire stretches and the wood responds to humidity fluctuations it takes a while for the piano to stabilize.  For home customers most manufacturers suggest twice yearly tunings to properly maintain the piano.  Institutional applications like churches or schools more commonly will tune and service their pianos four to six times per year. Professional applications like music clubs may tune as often as once per week. The Indianapolis Symphony will tune before every performance and most rehearsals which could be as often as five or six times per week. By following a maintenance schedule you will see many years of exceptional service from your piano.