upright piano action
What pianos are made from
Season and weather transitions are a good time to talk about how humidity changes can affect your piano. Pianos are made from a lot of familiar materials like wood, felt, leather, metal, and plastic with the main parts being made of wood.
Humidity and wood
Wood is hygroscopic meaning it absorbs moisture from the air. As relative humidity increases, wood absorbs more of that moisture, and desorbs, when relative humidity decreases. Water content in wood increasing can cause the wood to swell. On a piano this may take the form of the soundboard crowning more where the bridge is attached causing more tension on the strings and the pitch to therefore rise. The reverse is true as humidity decreases and wood dries and shrinks. The soundboard flattens and results in looser strings and lower pitch. In extreme cases of dryness, wood can form cracks and splits, which may need to be repaired in order for the piano to function or even make the piano unusable.
grand piano soundboard under plate, strings, & bridge