OCCLUSIVE AND PLOSIVE
Occlusives require a complete closure of the speech canal, not just a restriction. This distinguishes them from the continuants. The occlusion is twofold: (a) the airstream is halted by a sudden closure in the oral cavity; (b) the trapped air is freed by abruptly releasing the closure. If the trapped air is gradually released, an affricate consonant is articulated. Occlusives in English include /p/, /b/, /m/, /t/, /d/, /n/, /k/, /g/, and /ŋ/.
[p] is a voiceless bilabial stop consonant. The lips are pressed tightly together. The air is trapped behind the lips. The vocal cords are kept far apart, and the nasal cavity is closed by the velum. Then the trapped air is suddenly released. [b] is the voiced counterpart of [p]. The only difference is that the vocal cords are close to each other and vibrate during the articulation of [b]. In the case of /m/, the nasal cavity is open.
[t] is a voiceless dental or alveolar stop. The tongue makes contact with the front teeth or with the alveolar ridge directly above them. There is no vocal cord vibration and the nasal cavity is blocked. [d] is a voiced dental or alveolar stop. It is produced in the same way as [t] but with vibration of the vocal cords. In the case of /n/, the nasal cavity is open to let the air pass through it.
[k] is a voiceless velar stop. With the tongue tip resting against the lower teeth, the back of the tongue makes contact with the soft palate. [g] is its voiced counterpart. Its articulation is the same as [k], but with vibration of the vocal cords. The corresponding velar nasal [ŋ] is usually voiced as well.
Some languages, including Persian, have a glottal occlusive [ʔ] too. The glottal stop can be produced in either of the two ways: (a) by the sudden opening of the glottis under pressure from the air below, or (b) by the abrupt closure of the glottis to block the airstream. The glottal stop is always voiceless, as the complete closure of the vocal cords precludes their vibration.
Occlusives can be categorized into two major types: stops and plosives. The two categories are in inclusional distribution. That is, all plosives are stops but all stops are not necessarily plosive. This relationship can be schematically represented as:
Plosive sounds are made by forming a complete obstruction to the flow of air through the mouth and nose. The first stage is that a closure occurs. Then the flow of air builds up and finally the closure is released, making an explosion of air that causes a sharp noise. Try to slowly say /p/ to yourself. You should be able to feel the build up of air that bursts into the /p/ sound when you open your lips. It should be noted that a plosive cannot be prolonged or maintained so that once the air has been released, the sound has escaped. As such, plosive sounds lack the length feature. Contrast this quality of plosives with a fricative in which you can lengthen the sound. The plosive sounds in RP are: /b/, /p/, /t/, /d/, /k/, and /g/. As it was mentioned earlier, plosive sounds belong to a more general class of sounds called stops. A stop sound is one in which the flow of air is completely blocked only in the oral cavity. Stops also include such sounds as /m/, /n/, and /ŋ/. Take the following examples:
You can feel that in the production of such sounds as /m/, /n/, and /ŋ/ the flow of air is completely blocked in the mouth. However, air can flow through the nose. As such, the air cannot burst into these sounds because they can be lengthened. In addition to these sounds, /ʧ/ and /ʤ/ are also marked by a complete blockage of pulmonary air in the oral cavity. Here, again, the blockage is not followed by an abrupt release. Rather, the blocked air is gradually released to create friction. Some phoneticians rank these two sounds among the stop consonants while many others classify them as affricates. Take the following examples:
