N. V. Tatsenko introduction to theoretical phonetics of english

unctional differences between vowels (V) and consonants (C).

1. 
   The most substantial articulatory difference between vowels and consonants is that in the articulation of V the air passes freely through the mouth cavity, while in making C an obstruction is formed in the mouth cavity and the airflow exhaled from the lungs meets a narrowing or a complete obstruction formed by the speech organs. For example, in the case of [t] (Fig. 1), there is direct contact between the tip of the tongue (active articulator) and the alveolar ridge (passive articulator), so that the airflow coming from the lungs can leave the mouth cavity only when the obstruction is removed (fig. 3.2):
   

Figure 3.2 - Consonant [t]



In the case of [i:] (fig. 3.3), there is a gap within the mouth that is determined by the position of the tongue, and the airflow can escape relatively freely:




Figure 3.3 - Vowel [1:]
Another difference between consonants and vowels is that vowels are generally voiced, i.e. the vocal cords are set vibrating by the outgoing airflow. Consonants, by contrast, can be voiced or voiceless: The vocal cords are either far apart and do not vibrate, as in fan, or they are relatively closed and vibrate as in van (fig. 3.4).

Figure 3.4 - Voiceless and Voiced Sounds
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T he particular quality of Vs depends on the volume and shape of the mouth resonator, as well as on the shape and the size of the resonator opening. The mouth resonator is changed by the movements of the tongue and the lips. The particular quality of Cs depends on the kind of noise that results when the tongue or the lips obstruct the air passage. The kind of noise produced depends in its turn on the type of obstruction, on the shape and the type of the narrowing. The vocal cords also determine the quality of consonants.

2. 
   From the acoustic point of view, vowels are called the sounds of voice, they have high acoustic energy, consonants are the sounds of noise which have low acoustic energy.
   
3.