A soundboard is a thin, stiff, light weight, strong but elastic, and usually wooden, panel under or behind the strings of most string musical instruments that is forced to vibrate slightly by the vibration of the strings. It serves to amplify and enrich the relatively weak sounds made by the strings into full, strong sounds that can project through the air and is the most important factor in an instrument's sound.
Among the instruments that contain soundboards are pianos, violins, violas, cellos, basses, guitars, lutes, banjos and harps.
The optimal size, shape and specific type of wood or other material of the soundboard varies considerably according to the instrument. For upright pianos it is a large, thin wooden panel typically made of spruce wood at the rear of the instrument, whereas for grand pianos it is part of the case. The soundboard of a violin is the thin, arched wooden panel on the top of the instrument has two f-shaped sound holes cut into it to allow the sound waves to project outwards. The soundboard of a guitar is likewise its top panel.
Although soundboards are traditionally made of wood, other materials are used for some instruments, such as animal skin or plastic on instruments in the banjo family. The most common woods are spruce (Sitka or European) and cedar, as they offer the ideal combination of high stiffness-to-weight ratio and low density. Creating high quality soundboards is a highly skilled craft that includes determining the optimal wood, including its species, shape, thickness, grain pattern, how it is cut and sanded, and chemical treatments (to affect mechanical and acoustic properties as well as for moisture control, fungal suppression, etc.).