There are 3 main reasons why you want to keep the humidity within this range:
1. Tuning Stability One of the main reasons a piano goes out of tune is because the soundboard expands or swells when humid, and contracts or flattens out when dry. When it expands, it presses against the strings, which puts them under more tension causing the notes to become sharp, or higher in pitch. When the soundboard contracts, the tension on the strings loosen and the notes become flat, or lower in pitch. However, they don’t all become sharp or flat equally, so the piano goes out of tune.
2. Longevity The three major structural parts of the piano (the soundboard, the bridges and the pinblock), are made of wood and are susceptible to drying and cracking. This is likely to happen prematurely if the humidity is too low, but it is even more likely if the humidity swings from being very humid in the summer to very dry in the winter. In addition, if the piano is near direct heat, these cracks can develop even if the overall humidity is kept constant. Cracks in the soundboard and bridges can cause annoying rattles and buzzes that can be difficult and expensive to repair. If the pinblock becomes dried out, the tuning pins will slip and it will no longer hold a tune, even if the humidity is kept constant afterwards. Replacing the pinblock is a major rebuilding job, which requires restringing the piano and is fairly expensive.
3. Sticking and clicking notes The keys and the internal moving parts of the piano are called the action. These parts are made of wood and felt and are held in place with various screws and glue joints. If the action becomes too humid, the wood swells and notes can become sluggish, or stop working altogether. If the action becomes too dry, screws and glue joints can become loose, causing action noises and failing notes. In addition, the action parts’ relationship to one another, called regulation, is affected by changes in humidity and can change the touch or feel of the piano. These problems are kept to a minimum if the humidity inside the piano is kept constant and moderate.
What can you do to help keep the humidity levels under control?
1. Control room humidity The best way to keep a piano’s humidity stable is simply to keep the humidity of the room the piano is in stable. This can be done with a humidifier during the winter, and with a dehumidifier during the summer. Using a digital hygrometer will help to determine when either is needed. When the hygrometer shows that the humidity is below 40%, the humidifier should be turned on. If it shows above 50%, the dehumidifier should be turned on (newer models of both humidifiers and dehumidifier can often be set at a given humidity level making this much easier, but I recommend monitoring the humidity with a digital hygrometer to make sure).
2. Piano humidity control system This is a system that is installed inside a piano by a piano technician. These systems can be very effective and are easier to operate than room humidifiers/dehumidifiers, but they are a more expensive solution and they don’t humidify the rest of the room.
Ultimately, your piano is an investment that you want to protect. With proper humidity control, your piano will last longer, hold its tuning longer and play better. If you have questions on how to protect your piano, please contact us for more information.