sound-pendulum

Century Dictionary and Cyclopedia

1. n. In psychophysics, a pendulum suspended from a steel pillar, the hard-rubber bob of which strikes, as the pendulum falls, upon a block of ebony cemented to the base of the instrument. Since the intensity of the sound produced by the blow is directly proportional to the height of fall of the bob, that is, to the square of the sine of half the arc through which the pendulum swings, the relative intensities of successive sounds may readily be calculated by reference to a graduated arc of metal, also attached to the base of the instrument. The sound-pendulum is sometimes made with two pendulums, hung to right and left of the pillar and striking on the two faces of the block: but it is difficult to insure the qualitative similarity of the two sounds thus produced. The sound-pendulum was first constructed by Volkmann, and since Fechner's time it has been a standard piece of psychophysical apparatus.