The airstream mechanism is mandatory for most sound production and constitutes the first part of this process, which is called initiation.
[4] [4]Any of the three principal initiators − diaphragm, glottis or tongue − may act by either increasing or decreasing the pressure generating the airstream.
The only attested use of a phonemic pulmonic ingressive is a lateral fricative in Damin, a ritual language formerly used by speakers of Lardil in Australia.
The glottis must be fully closed to form glottalic egressives, or the air column would flow backwards over it; it is therefore impossible to pronounce voiced ejectives.
Ejective allophones of voiceless stops occur in many varieties of English at the ends of intonation units.
[8] For ingressive glottalic initiation, the sequence of actions performed in glottalic pressure initiation is reversed: one raises the glottis (as if to sing a high note), closes it, and then lowers it to create suction in the upper trachea and oral cavity.
Instead of keeping the glottis tightly closed, it is tensed but left slightly open to allow a thin stream of air through.
Unlike pulmonic voiced sounds, in which a stream of air passes through a usually-fixed glottis, in voiced implosives a mobile glottis passes over a nearly motionless air column to cause vibration of the vocal cords.
Phonations that are more open than modal voice, such as breathy voice, are not conducive to glottalic sounds because in these the glottis is held relatively open, allowing air to readily flow through and preventing a significant pressure difference from building up behind the articulator.
Because the oral cavity is so much smaller than the lungs, vowels and approximants cannot be pronounced with glottalic initiation.
So-called glottalized vowels and other sonorants use the more common pulmonic egressive airstream mechanism.
Similarly, fully voiced stops in languages such as Thai, Zulu, and Maidu are weakly implosive.
This ambiguity does not occur with the next airstream mechanism, lingual, which is clearly distinct from pulmonic sounds.
Even when not ejective, it is not uncommon for the glottis to be closed as well, for a triply articulated consonant, and this third closure is released last to produce a glottalized click.
The velum is lowered so as to direct pulmonic airflow through the nasal cavity during the lingual initiation.