Factors that affect tuning stability and the importance of regular maintenance.
A common question we hear at Piano Inside is, "How long will my piano stay in tune?" The truth is, a piano begins to go out of tune the moment the technician leaves your home. A piano's strings are under nearly 20 tons of combined tension, and they constantly want to stretch and relax. However, the biggest enemy of tuning stability is not playing, but humidity. As the seasons change in Toronto, the wooden soundboard expands and contracts, pushing and pulling the strings. For a piano kept in a climate-controlled room, a tuning will typically sound great for about 6 months. For serious musicians, or pianos exposed to drafts and sunlight, quarterly tuning is recommended to maintain a perfect A440 pitch.
Inside an average acoustic piano, there are over 220 steel strings. When pulled up to standard A440 pitch, these strings exert an incredible 18 to 20 tons of tension on the cast iron plate and wooden structural frame. Because steel is slightly elastic, the strings are constantly trying to pull themselves loose. A master tuner carefully 'sets the pin' in the wooden pinblock to counteract this, but physics dictates that the tension will inevitably drop over time.
While string stretching is a factor, changes in relative humidity cause the most drastic pitch fluctuations. The piano's soundboard is a large, thin sheet of spruce. During the humid Toronto summer, the wood acts like a sponge, swelling upward and pushing the bridge against the strings, causing the pitch to go sharp. In the dry winter, the wood shrinks, the soundboard flattens, and the pitch goes flat. Keeping your indoor humidity strictly between 40% and 50% year-round is the absolute best way to keep your piano in tune longer.
If you play occasionally and your home has central air conditioning and a humidifier, bi-annual (twice a year) tuning is generally sufficient. The ideal times are a few weeks after you turn your heat on in the winter, and a few weeks after you turn your AC on in the summer. If the piano goes for years without tuning, the pitch will drop so far that a standard tuning will no longer be possible; instead, it will require a specialized, more expensive process called a 'Pitch Raise' before it can be finely tuned again.