Abstract
Diplophonia is the simultaneous presence in the voice of two separate tones, heard as distinctly different in pitch. While permanent diplophonia is a somewhat rare phenomenon, transient bitonality is frequently noticed in patients either with lesional or functional hoarseness. Diplophonia was observed in 72 patients, and various acoustical, visual and glottographical techniques of investigation were performed. Acoustically, diplophonia is due to the addition of a second subharmonic series to the normal F 0 harmonic structure. Mechanically, diplophonia is always associated with abnormal oscillatory movements of the vocal folds involving a double or multiple phased closing or opening movement of the glottis, or a beating phenomenon of the two folds oscillating at different frequencies. As a general rule, diplophonia is associated with excessive air escape through the glottis, which is a cause of hoarseness. Diplophonia is not a specific characteristic of a particular aetiology of dysphonia.
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