3. Vowels are speech sounds produced with no obstruction to the air flow coming from the
lungs. Vowels take on their different sound qualities by subtle changes of shape in the
vocal tract as they are being produced.
For example, in producing the vowel sound /i:/ as in bean, the lower and upper jaw are
quite close together and the front part of the tongue is slightly raised towards the roof of
the mouth, while in producing /u:/ as in boon, it is the back part of the tongue is raised. In
producing /a:/ as in barn, the jaws are quite far apart, and it is the central part of the
tongue which is slightly raised. Vowels are also differentiated by the degree to which the
lips are rounded or spread, e.g. /i:/ is made with spread lips, /u:/ with rounded lips and
/a:/ with the lips in a neutral position. Finally, vowels will vary in terms of their length how long they are held. The /e/ in pet is short vowel compared to the /u:/ in boon.
4. The English diphthongs in the chart above are illustrated in the words bite,
bait, boy, toe, house, poor, ear, and air.
