Humidity Control
The following information is copied in large part from Technical Bulletin #3 published by the Piano Technicians Guild. It is available from me or at the PTG website.
Your piano is made primarily of wood, a versatile and beautiful material ideal for piano construction. However, being made of wood, your piano is greatly affected by humidity. Seasonal and even daily changes in humidity cause wood parts to swell and shrink, affecting tuning stability and touch. Extreme swings in humidity can eventually cause wood to crack and glue joints to fail.
Other materials in your piano also are affected by changes in moisture content in the air. The many felt and leather parts in your piano's action can change dimension, affecting regulation and friction, or stiffness of the touch. Very high humidity can even create condensation on metal parts such as strings, tuning pins and hardware, eventually causing them to rust.
How does humidity level affect my piano's tuning?
S
welling and shrinking of the piano's soundboard is the most immediate and noticeable effect of humidity change. The soundboard, a sheet of wood approximately 3/8 of an inch thick, is made with a slightly crowned shape. The strings pass over the soundboard and are connected to it by a wooden piece called a bridge. The upward crown of the soundboard presses the bridge tightly against the strings.
As the moisture level in the soundboard increases during periods of high relative humidity, the crown expands and pushes the bridge harder against the strings. The strings are stretched tighter and the piano's pitch rises. Because this increase in crown is greater in the center of the soundboard than at the edges, the pitch rises more in the middle octaves than in the bass or treble registers.
During periods of low relative humidity the soundboard shrinks, reducing the crown and decreasing pressure against the strings. The pitch drops, again with the greatest effect noticeable in the center of the keyboard. When relative humidity returns to its previous level, the average pitch of all the strings will return to normal, although the exact pitch of individual strings will be slightly changed from their original settings. Thus, a piano will only stay in tune as long as the relative humidity level in the air surrounding the soundboard remains constant. Extreme humidity changes require making greater changes in string tension to bring the piano back into tune. This upsets the equilibrium between the string tension and the piano frame, and the piano never becomes stable.
Try this test on your piano. Play octaves. Start with those encompassing middle C and play octaves chromatically downward for about 2 octaves. Some of these octaves will most likely sound worse than others. If this is the case, your piano has succombed to a seasonal change in tuning. It is out of tune. What can be done to minimize humidity problems?
Keeping the humidity level around your piano as constant as possible will help it stay in tune longer as well as slow such damage as soundboard cracks, loose tuning pins, and glue joint failures. The first and simplest precaution you can take is to position your piano away from areas where it would be exposed to extremes of temperature and humidity such as heating and cooling vents, stoves, doors and windows. Direct sunlight is especially damaging. If your home is not well insulated, an interior wall is preferable to an outside wall.
Controlling the humidity within the home is another step you can take to preserve your instrument. In most areas of the country the relative humidity is very low during the cold winter season, and very high during the spring and summer. You have probably noticed the symptoms of low RH (shocks from static electricity when sliding out of a car or after walking across carpet), and the signs of high RH (limp, soggy-feeling newspapers and sticking doors).
Use of a room humidifier during dry seasons will help somewhat. However, too much moisture added to a room during winter months can cause condensation to form on cold surfaces such as windows, eventually causing mildew, rot, and, in extreme cases, damage to the building structure. During the humid season dehumidification is needed. Humid summer situations require much more elaborate dehumidification systems. Unfortunately, it is seldom possible to adequately control the relative humidity of a piano by controlling the room environment alone.A very practical and effective answer to humidity problems is to have a humidity control system installed in the piano itself. These systems consist of three parts:
- a humidifier for adding moisture to the air
- a dehumidifier for eliminating excess moisture
- a humidistat or control unit which senses the RH of the air within the piano and activates the system to add or remove moisture as needed
These systems are designed to maintain the RH of the air within the piano at the ideal level of 42%. The components are installed out of sight, inside the case of a vertical piano or under the soundboard of a grand. They are easy to maintain, and I can install one in your piano.What do you recommend?
I recommend the Piano Life Saver by Dampp-Chaser. I have personally witnessed very wild unstable pianos become very stable with the addition of one of these systems. I purchased a low quality piano with a reputation for instability for myself so that I could monitor the results of a system installation on a daily basis. The improvement has been amazing and I strongly recommend this as a valuable addition to your instrument.
How will humidity control benefit my piano?
While not eliminating the need for regular piano maintenance, humidity control will allow more stable tunings by reducing the radical pitch changes your piano may experience through the seasons. When your piano stays closer to its correct pitch level of A=440, I do not have to perform a large pitch raising or lowering procedure prior to fine tuning. Thus, a balance of forces is maintained between the strings and the frame of the piano, allowing more accurate and stable tunings to be done.
In addition, a stable environment will help to preserve your piano through the years. Wood parts, glue joints, metal parts and your piano's finish will all last longer if not subjected to excessive humidity swings. Maintaining the correct environment will preserve your piano investment for a lifetime of enjoyment. 