Soundboards         A string is unable to radiate sound on its own, so a soundboard is required as an amplifier for the vibrations. The string vibrations displace the air, but because of a small surface area on the string, only a small sound can be heard. A bridge links the strings to the soundboard and transmits the vibrations and energy to project the sound into the air. A piano’s soundboard is described as a musical diaphragm, and should always be under tension by having an arch or “crown” in the center of the board.         In order for the sound board to vibrate freely it must be a very thin panel of wood, this is the only material known to amplify music well. Humidity in the air can be absorbed by the wood and cause it to expand which increases the tension in the strings and raises the piano’s pitch. If the wood were to dry out, the pitch would decrease.                                                 http://www.steinway-piano.com/steinway-grand-piano/steinway-model-d-made-of-wood-glue-and-metal/         The string tension on a modern grand piano (not all common pianos) can be as high as thirty tons, and to withstand that tension a piano must have an immensely sturdy frame. A piano will have an iron plate acting as a support system for the strings. The resonance of the plate aides in producing a piano’s tone.