Vocal Tract Resonance

Sundberg models the vocal tract as a closed tube resonator, suggesting that the three prominent formants seen in vowel sounds correspond to the harmonics 1,3,5. These frequencies are then modified by the cavity resonance of the vocal tract as influenced by the articulators.

A typical length for the vocal tract is about 17-18 cm. This would give a fundamental frequency of about 500 Hz if it is treated as a closed cylinder. This would predict formant frequencies of 500, 1500 and 2500, which is in the range of observed frequencies. However, the articulators which provide differences in vowel sounds produce significant changes in these formant frequencies.

Voice Articulators

In order to produce distinguishable voice sounds, like vowel sounds, the vocal mechanism must control the resonances of the vocal tract which produce the characteristic vocal formants. If the vocal tract is considered to be a cavity resonator, then it can be seen that the position of the tongue, the area of opening of the mouth, and any changes which affect the volume of the cavity will retune the resonance.

Voice Articulators

Voice articulation is seen as the changes in the resonances of the vocal tract, and the agents of such changes can be called articulators. Movement of the tongue, pharynx, palate, jaw, or lips can change the basic factors which determine the frequency of cavity resonance (volume of cavity, area of opening, and port length) .

Voice articulation produces sounds which are called vowels, dipthongs, semivowels, and nasals. Such sounds can be considered to be modifications of the basic vocal tract resonance, a kind of filtering of the acoustic spectrum of the voice mechanism.

While the resonances for most voiced sounds are in the pharyngeal and oral cavities, the nasal sounds /m/, /n/, and /ng/ require added resonance in the nasal cavity.