The Loudness of tone depends upon the amplitude of the vibrations. This is easily shown by drawing a bow over the string of a violin: while the vibrations of the string are largest, the tone produced is loudest, and as the vibrations get smaller, so the tone becomes fainter.
The Pitch of tone depends upon the number of vibrations in a given period of time. The greater the number of vibrations the higher the pitch, and vice versâ.
The Quality of tone depends on the form of the vibrations, "which also determines the occurrence of upper partial tones."[K]
Now, to make the sound of any tone-producing element more intense, and to give it some special quality, is the work of the resonator. If we simply fix a fiddle string at either end, and, after giving it a certain amount of tension, draw a bow across it, we shall certainly produce a tone, but a very poor and faint one. Put the same string with the same amount of tension upon a cheap violin, and the tone will be intensified, and its quality changed, though that quality may be of a very unpleasant kind. Repeat the experiment upon an Amati or a Straduarius, and not only will the tone be more powerful still, but it will also have a full, round, and beautiful quality. Something, it is true, depends upon the string and upon the bowing, but we are here supposing the same string and the same player, our object being to show how the resonator, which, in this case, is the body of the violin, intensifies the tone of the string, and affects its quality.
Illustrations exemplifying the same thing might be multiplied to any extent, but the one I have just given will suffice. As with the string, so with the vocal ligaments. Cut a larynx out of a dead body, put it in proper position on the top of a bellows, and force the air through it, and you will produce tone, but faint and poor tone. Now add a resonator to the larynx, and the tone of the vocal ligaments will be intensified, and its quality altered according to the kind of resonator you make use of.
It is clear, therefore, that the human voice does not only depend upon the vibrations of the vocal ligaments, and the corresponding vibrations of the air passing between them, but also upon the resonator as defined on p. 9. According to the natural formation of our resonator, and according to the infinite variety of shapes which every one has it in his power to give to it, our voices will be, always supposing the conditions of the vocal ligaments to be the same, either full, round, sonorous, and beautiful, or they will be poor, cutting, muffled, guttural, nasal, and ugly.
As we have, or may easily acquire, absolute command over the resonator, or, at least, over the greatest part of it, it is a comfort to know that so very much depends upon it, and I trust my readers will now, with some amount of pleasure, look with me at this part of the vocal apparatus.
The 1st and 2nd divisions of the resonator—namely, the pockets of the larynx and the tube above the pocket ligaments—have been fully described on pp. 52, 53, and no more need be said on the subject here.
The upper part of the throat, called in scientific works the "Pharynx" ([pl. I], P), is a cavity, the largest part of which may be seen through the arch at the back of the open mouth. Its hinder wall is formed by the spinal column, and it extends upwards as far as the Eustachian tubes ([pl. I], E) which communicate with the middle part of the ear. Here it joins—
The Cavities of the Nose ([pl. I], N), which have for their base the hard and soft palate ([pl. I], H and S), and which are divided by a bone partition.