The art of music, Vol. 05 (of 14)

by Unknown

III

What was said about the uncertainty of our present knowledge concerning the laryngeal action applies with almost equal force to the other operations of tone production. Beyond the basic facts that the tones of the voice are produced by the vibration of the vocal cords and are reinforced and modified by the influence of the resonance cavities, little can be stated with absolute certainty. There is, of course, no question as to the definiteness of our knowledge of the anatomical structure of the parts involved. But, with regard to the muscular operations of the resonance cavities and the application of acoustic and mechanical principles in these operations, the same uncertainty is encountered as in the laryngeal actions. We shall continue therefore to outline the most widely accepted theories, without entering into a discussion as to their soundness.

Considered acoustically, the voice is a wind instrument of the reed class. It differs, however, from all other reed instruments in several particulars. It is capable of producing a wide range of pitches, covering more than three octaves in many cases, by the operation of a single pair of reeds. Further, it has command of an immense range of tone qualities, through the combined action of its reed mechanism and its resonating cavities.

For the production of tone the vocal cords are brought together and held on tension with sufficient strength momentarily to close the glottis and check the outflow of the expired breath. As a slight degree of condensation takes place in the air behind the cords, they are forced apart and a tiny puff of air is allowed to escape. Immediately the cords spring back, once more close the glottis, and again check the outflow of the breath. This is repeated a varying number of times per second, the rate of rapidity of the succession of puffs being regulated by the degree of tension of the vocal cords, and by their effective vibrating length. The pitch of the tone thus produced is determined by the rate of the air puffs; these range from 75 per second for the lowest usual bass note,

to 1,417 per second for the highest usual soprano note,

.

The tone produced by the vibration of the vocal cords is complex in its acoustic character, containing the fundamental note and a large number of its overtones. Yet as it leaves the cords the tone is weak in power and of rather characterless quality. In order to be of musical quality, volume, and carrying power, the primary or vocal cord tone requires to be modified and reinforced by the resonance cavities.

The resonating cavities of the voice, mastery of which is considered essential to the scientific management of the voice, are the chest, the mouth-pharynx, the nasal passages, and the sphenoid, ethnoid, and frontal sinuses. Each of these is adapted by its size and shape to reinforce either the fundamental note or certain of its overtones with especial prominence. In order to produce a satisfactory tone each resonance cavity must exercise its particular influence in the proper way, their combined effect being necessary to a correct use of the voice.

Much importance is attached by most vocal authorities to the subject of chest resonance. It is believed that the size of the chest cavity,[1] much greater than that of the other resonating spaces, adapts it especially to the reinforcement of the fundamental note and its lower overtones.[2] The mouth-pharynx cavity is capable of extreme variability in both size and shape. This mobility enables it to reinforce a wide variety of overtones, and so to exercise a most important influence in determining the quality of the tone. Another function of this cavity is to increase the power of the primary or vocal cord tone. To secure the effect of crescendo in a single tone, the force of the expiratory blast is gradually increased. In order that the tone may be of uniform musical quality as it swells from soft to loud, a corresponding increase must take place in the size of the mouth-pharynx cavity. This is effected by the gradual opening of the mouth by a lateral expansion of the pharynx and by a lowering of the base of the tongue. A slight elevation of the soft palate may also contribute to the expansion of the cavity.

A highly important feature of mouth-pharynx resonance is the forming of the various vowel sounds. Each vowel is simply a distinct quality of sound, caused by the special prominence of some one or two overtones. Helmholtz investigated this aspect of voice production exhaustively. At first thought, it seems strange that a tone on some one pitch gives the effect of a particular vowel. Yet we can readily hear this in the steam siren whistle commonly used for alarms of fire. This produces a screaming sound, caused by a gradual rise and fall of pitch through a range of several octaves. Its almost vocal effect of ‘Ooh-oh-ah-eh-ee’ gives us a clear idea of the manner in which these vowels are each the sound of a note somewhat higher than the one preceding.

Helmholtz gives as the determining notes for certain of the German vowels the following table:

For each vowel the mouth-pharynx must assume a shape and size adapted to reinforce with special prominence its particular note or notes. Anyone can readily observe for himself what the positions of the tongue and lips are for the various vowels. For ee the tongue is arched high in the mouth and the lips are only slightly parted. For ah the mouth is opened slightly wider, while the tongue lies flat, etc.

No variation can be made in the size or shape of the nasal and head cavities. As these hollow spaces are small and very various in form, they reinforce only the higher overtones. Special prominence given to the higher upper partials[3] has the effect of making the tone brilliant and somewhat metallic in quality, and it is here that the special function of nasal resonance is seen. A certain degree of nasal resonance is therefore essential to the correctly used voice, but this must be kept within well-defined bounds. Excessive prominence of this resonance is the cause of the unpleasantly nasal sound which is absolutely out of place in correct tone production.

There remains to be treated under this head the production of consonant sounds. Consonant sounds are of various acoustic characters and are formed in a variety of ways. They may best be considered as of two classes: those into which a tone produced by the vocal cords enters and those devoid of this element. The other determining factor in consonant formation is the point at which an interruption takes place in the outflow of the breath.

There are a number of allied pairs of consonants, one with and the other without an accompanying vocal sound. These are:

v and f
b and p
z and s
d and t
j and ch
th (as in that) and th (as in think)
z (as in azure) and sh
g and k

In each of these pairs the interruption takes place at the same point—v and f between the lower lip and the upper teeth, b and p at the lips, etc.

Another class of consonants are the so-called sonants or liquids, l, m, n, and ng. In these the vocal tone may have appreciable duration; we can hum a tune on any one of them; m, n, and ng are emitted solely through the nostrils, the orifice of the mouth being completely closed.

R may be pronounced in two ways, the trilled or rolled r being best for the purposes of singing. Another form of this consonant, made by the vibration of the uvula in contact with the back of the tongue, is essential to a correct (conversational) pronunciation of both French and German, although it has no place in English. The rolled r, however, is generally used in singing by both the French and the Germans.