Transverse and torsional modes of vibration of American organ reeds

Abstract

A reed from an American reed organ consists of a brass tongue riveted to a frame with an opening just large enough for the reed to pass through during the course of its oscillation. To a first approximation, the reed tongue can be modeled as a cantilever beam of uniform cross section, and the mode frequencies of transverse and torsional modes can be calculated. The reeds used in this study differ from this simple model in several ways, including a nonuniform thickness along the reed length. In addition, the reed includes a curved spoon-like section at the tip of the reed tongue as well as an asymmetric twist at the tip. Transverse and torsional modes of vibration of a mechanically excited reed tongue have been studied using a proximity sensor (variable impedance transducer), a laser vibrometer, and a TV holography system. The motion of the air-driven reed has also been investigated. Although the motion of air-driven reed is dominated by the first transverse mode, some evidence of higher-order transverse modes and torsional modes has been observed. [Work supported by the NSF from REU Grant No. 0139096.]