[The monochord, its path from Pythagorean musicology to testing the upper auditory tone limit. Pictures from the history of otorhinolaryngology, represented by instruments of the Ingolstadt German Medical History Museum].
The monochord consists of a frame with a string or pianowire stretched across it. The length of the wire can be varied by a movable bridge. The string or wire is plucked, hit, or bowed, producing transverse vibrations. In this mode the number of vibrations per second is dependent on the length, tension, and thickness of the string. In ancient times, the Pythagoreans used such an instrument to study the natural laws underlying musical intervals; in the 19th century it also served for various other physical experiments. F. A. Schulze, physicist in Marburg, Germany, introduced the monochord for testing the upper tone limit in 1908. He produced longitudinal vibrations by rubbing the wire with a piece of felt moistened with benzol. The vibrations of this mode are dependent only on the length of the wire and the elasticity of the material; they are independent of its tension and thickness. H. J. L. Struycken, otologist in Breda, Holland, presented an improved type of monochord in 1910 which also allowed testing bone conduction. K. L. Schaefer, physiologist in Berlin, modified Struycken's instrument in such a way that bowing the wire or hitting it with a small hammer also produced transverse vibrations. This enlarged the range of tones in the lower region. In this combined version the monochord was an indispensable piece of hearing testing equipment before the era of electronic audiometers. The technical development and clinical application of the monochord is described in detail.