A series of resonating air chambers above the larynx alter the overtones to create the human voice.
There are three major resonating cavities above the larynx: The Pharynx, the Nasal Cavity and the Oral Cavity.
The pharynx (not the be pronounced ‹pharnyxŠ) is the area directly above the the larynx, in the back of the throat up to the oral cavity.
It is not typically changed during speech, although under conditions of overall body tension, it can be constricted.
Modulator: The complex tone produced by the larynx alone does not particularly sound human. It is the action of the resonating air chambers above the larynx that shape the sound into its human form by screening, and hence modifying, the pattern of overtones.
Air in an open area does not typically resonate, but in an enclosed areas, such as a bottle it will. Hence, the cavities in the air channels leading to the larynx can serve as resonators.