SOUND-Board, the principal part of an organ, and that which makes the whole machine play. It is a reservoir into which the wind, drawn in by the bellows, is conducted by a port-vent, and thence distributed into the pipes placed over the holes of its upper part. The wind enters them by valves, which open by pressing on the keys, after the registers are drawn, by which the air is prevented from going into any of the other pipes, besides those in which it is required.

SOUND Board also denotes a thin broad board placed over the head of a public speaker, to enlarge or extend and strengthen his voice.

Sound-boards are found by experience to be of no use in theatres, as their distance from the speaker is too great to be impressed with sufficient force. But sound-boards over a pulpit have frequently a good effect, when the case is constructed of a proper thickness, and according to particular principles.

SOUND-POLE, is a post placed in the inside of a violin, &c. as a prop between the back and belly of the instrument, and nearly under the bridge.