What is the airstream mechanism?

Speech is audible because the movements of articulators (to be discussed in subsequent sections) cause the air to vibrate, forming sound waves which travel to the hearer’s ears, and set up vibrations in her inner ear, which are then translated into sounds again by the brain. Since sound waves need air, it follows that articulatory vibrations will only make sound waves if there is a moving body of air available. Airstreams can be set in motion, or initiated, in three ways; however, only one is used in English, and indeed is found in every language of the world.

Essentially, speaking is modified breathing: it makes use of the resources involved in normal respiration, but in a more controlled way. When we are simply breathing quietly, the phases of breathing in and out last approximately the same time, and expiration is not under our physical control; it simply occurs as an automatic consequence of having breathed in. However, when we are speaking, the phase of breathing out is significantly longer, depending on the length of the utterance we want to produce. A network of muscles, like the intercostal muscles between our ribs, come into play to make breathing out smoother, more gradual and more controlled during speech, providing a regular flow of air which can then be modified by the articulators in various ways.

All the sounds of English, both consonants and vowels, are produced on this pulmonic egressive airstream, where the initiator is the lungs and the rest of the respiratory system, and the direction of airflow is outwards: this is overwhelmingly the most common airstream mechanism in every language of the world. It can generally be taken for granted that the sounds under discussion below are pulmonic egressive, but you should remember to give that information in a complete description: so the labial nasal [m] (which, as we shall see, is produced using the lips – hence labial, and with airflow through the nose – hence nasal), is strictly a pulmonic egressive labial nasal.

It is possible to produce speech using a pulmonic ingressive airstream. No language seems to use this airstream regularly for particular sounds, although it has been reported in various cultures as a means of voice disguise: if you try to breathe in and speak at the same time, you will find that the pitch of your voice raises significantly.

There are two other airstreams which may be involved in speech, although even in languages where these are used, they will characterize only a few sounds, interpolated in a stream of pulmonic egressive speech. The first is the glottalic airstream mechanism, initiated by a movement of the larynx, which is where you can feel your ‘Adam’s apple’ protruding slightly about half-way up your throat. The larynx can move up or down, and the glottalic airstream can therefore be either ingressive or egressive, producing sounds known as implosives and ejectives respectively; none of these occur in English. Finally, the ‘tut-tut’ click sound [l] is produced on a velaric airstream, which operates only ingressively. When you make [l] you can feel that the back of your tongue is pressed against the roof of your mouth, stopping air from moving any further back; a little air is then drawn into the mouth further forward, and the closure with the tongue is released to make a click. Neither the glottalic nor the velaric airstreams provide airflow with the volume or controllability of the pulmonic system.