Sound-board
A thin sheet of spruce-pine, or fir, upon which the bridge that supports the strings of the pianoforte rests. The function of the sound-board is to increase the volume of the tone, which it does by taking up the vibration of the string.
There are many unsolved problems in the relation which subsists between the string and the sound-board, as to the manner in which this amplification of the sound takes place. It is impossible to form a conception of the complications in the mode of vibration of the sound-board that must take place when, for example, a full chord is struck. Yet all these complications are not only simultaneous, but they obey the changing conditions of the most rapid execution with such swiftness and certainty that not a note is lost or a tone quality obscured.