8. The breath which has passed between the vocal chords and issues from the windpipe passes through the mouth, or through the nose, or through both. This is rendered possible by a soft movable flap which can at will be made to close the way through the nose, or—hanging loosely—to leave both passages open. Take a small mirror and look at the inside of your mouth, standing so that as much light as possible falls into it; you will see this flap, the velum, hanging down with a kind of ᐯ in the centre, the lower extremity of which is known as the uvula. Still watching your mouth, inhale through the nose and exhale through the mouth; see how the velum moves as you do this. After a little while try to move the velum, closing and opening the nose passage, without uttering a sound and without breathing.
In French there are four nasal vowels (occurring in un bon vin blanc) in which the velum hangs loose, and breath passes through nose and mouth. In standard English such vowels do not exist, but another form of nasal vowel, producing a "twang," is sometimes heard in many forms of what may be called dialect speech. The Londoner is often careless about closing the nose passage, and some breath is allowed to pass out by that way so as to be perceptible to the ear in the form of friction, and to impair the quality of the vowels. The "nasal twang" is very noticeable in some forms of American English.
The nasalising tendency may also be observed in untrained singers and public speakers; it is undoubtedly a means of increasing the carrying power of the voice, and of reducing the effort of making oneself understood by a large audience. The same effect can, however, be produced by training the muscles of the chest by means of breathing exercises, and with more agreeable results to the ear.
Pupils who show a tendency to nasalising can be cured by frequent exercises in uttering the mouth (or oral) vowels.
It is, however, maintained by some teachers of voice production that the best vowel sounds are produced when the velum does not quite prevent the passage of air through the nose.
In producing a nasal consonant (such as m), we stop the breath somewhere in the mouth (e.g. at the lips when we utter m), and let it pass out through the nose.
A cold in the nose often prevents the breath from passing through it; and this renders it impossible to produce the nasal consonants m, n, and ng (as in sing), the kindred sounds b, d, and g being substituted for them. A similar difficulty is experienced by children with adenoid growths. This is commonly called "speaking through the nose"; it is just the reverse.
9. In speaking, as a rule, the passage to the nose is closed and the breath finds its passage through the mouth. The shape of this passage can be modified in many ways, because several organs of speech are movable.
The lower jaw can be moved up and down.