A part of the vocal tract which is actively involved in the production of a particular sound, especially one which is used to form the primary constriction in the production of a consonant. Typically articulators are used in pairs, with one moving more than the other; the one that moves more is called the active articulator, and the other is the passive articulator. For example, in alveolar sounds (such as t), the active articulator is the tongue tip and the passive articulator is the alveolar ridge. (Sometimes the tongue is described as the articulator for vowels. )