Page:An outline of English phonetics ... with 131 illustrations (IA cu31924027389505).pdf/29

Rh *51. Zünd-Burguet’s Voice Indicator (fig. 7) is a convenient instrument for testing the presence of voice.

The flat side of the instrument is placed firmly against one side of the larynx, and when voiced sounds are produced the instrument rattles, though when breathed sounds are produced it remains silent.

*52. The presence or absence of voice may also be tested by means of the kymograph (see Chap. XXI).

53. Every speech sound belongs to one or other of the two main classes known as Vowels and Consonants.

54. A vowel (in normal speech ) is defined as a voiced sound in which the air has a free passage through the mouth, and does not produce any audible friction. All other sounds (in normal speech ) are called consonants.

55. Consonants therefore include (i) all sounds which are not voiced (e.g. p, s, h), (ii) all sounds in which the air has an impeded passage through the mouth (e.g. b, l, rolled r), (iii) all sounds in which the air does not pass through the month (e.g. m), (iv) all sounds in which there is audible friction (e. g. f, v).

56. The distinction between vowels and consonants is not an arbitrary physiological distinction. It is in reality a distinction based on acoustic considerations, namely on the relative sonority of the various sounds. Some sounds are more sonorous than others, that is to say