Phonetics - Unit One - Lesson No. 4
There are some mechanisms through which speech is produced. These mechanisms are: airstream mechanism, the phonation process, oronasal process and glottalic mechanism and velic closure.
The airstream process includes all the ways of pushing air out and sucking it in that provide the power for speech.
It is the name given to the actions of the vocal folds. Voiced sounds are produced with the vocal folds are vibrating and voiceless sounds are produced without vibration of vocal folds, e.g. [p, t, k and b, d, g].
The possibility of the airstream going through the mouth, as in [v] or [z], or the nose and in [n] and [m] is determined by the oronasal process. The uvular is the only organ deciding either of the two possibilities: when it lowers, the sounds are nasal; when it goes up, the sounds are oral.
When making a glottal stop, the air in the lungs is contained below the glottis. Then the air in the vocal tract itself will form a body of air that can be moved. An upward movement of the closed glottis will move this air out of the mouth. A downward movement of the closed glottis will cause air to be sucked into the mouth. When either of these things occurs, there is said to be a glottalic airstream mechanism.
The soft palate is a muscular flap that can be raised to press against the back wall of the pharynx and shut off the nasal tract, preventing air from going out through the nose. In this case, there is said to be a velic closure. This action separates the nasal tract from the oral tract so that the air can go out only through the mouth.