Description of a sounding board in Attercliffe church

The church at Attercliffe had long been remarkable for the difficulty and indistinctness with which a voice from the pulpit was heard. These defects have been completely remedied by the erection of a concave sounding-board, having the form resulting from half a revolution of one branch of a parabola on its axis. It is made of pine wood; its axis is inclined forwards to the plane of the floor, at an angle of about 10° or 15°; it is elevated so that the speaker’s mouth may be in the focus; and a small curvilinear portion is removed on each side, so that the view of the preacher from the side galleries may not be intercepted. A curtain is suspended from the lower edge for about 18 inches on each side. The effect of this sounding-board has been to increase the volume of sound to nearly five times what it was before; so that the voice is now audible, with perfect distinctness, even in the remotest parts of the church, and more especially in those places which are situated in the prolongation of the axis of the paraboloid. But the side galleries are also benefited; probably from the increase of the secondary vibrations in a lateral direction. Several experiments are related illustrative of these effects; among which, the most striking, was one in which a person placed so as to have one ear in the focus of the paraboloid, and the other towards another person speaking from the remote end of the church, heard the voice in a direction the reverse of that from which it really proceeded.