English Vowel sounds

In human speech, a sound in which the flow of air from the lungs passes through the mouth  with minimal obstruction and without audible friction is called a vowel sound such as the i in “fit,” and the a in “pack.” Although usually produced with vibrating vocal cords, vowels may be pronounced without such vibration, resulting in a voiceless, or whispered, sound. From the viewpoint of articulatory phonetics, vowels are classified according to the position of the tongue and lips and, sometimes, according to whether or not the air is released through the nose.

According to position of tongue a division of vowels can be made into front, central, back, close, half-close, half-open and open vowels.  According to the shape of lips the vowels also can be classified as rounded  and unrounded vowels.