Physiology Of The Voice
In former times the culture of the singing-voice was conducted upon
purely empirical grounds. Teachers followed a few good rules which had
been logically evolved from the experience of many schools of singing.
We are indebted to modern science, aided by the laryngoscope, for many
facts concerning the action of the larynx, and more especially the vocal
cords in tone-production. While the early discoveries regarding the
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mechanism of the voice were hopefully believed to have solved all
problems concerning its cultivation, experience has shown the futility
of attempting to formulate a set of rules for voice-culture based alone
upon the incomplete data furnished by the laryngoscope. This instrument
is a small, round mirror which is introduced into the throat at such an
angle, that if horizontal rays of light are thrown upon it, the larynx,
which lies directly beneath, is illuminated and reflected in the mirror
at the back of the mouth-- the laryngoscope. Very many singers and
teachers, of whom Manuel Garcia was the first, have made use of this
instrument to observe the action of their vocal bands in the act of
singing, and the results of these observations are of the greatest
value. Still, as before said, the laryngoscope does not reveal all the
secrets of voice-production. While it tells unerringly of any departure
from the normal, or of pathological change in the larynx, it does not
tell whether the larynx belongs to the greatest living singer or to one
absolutely unendowed with the power of song. Also, the subject of vocal
registers is as vexing to-day as ever.
While, then, we may confidently expect further and more complete
elucidation of the physiology of the voice, there is yet sufficient data
to guide us safely in vocal training, if we neglect not the empirical
rules which the accumulated experience of the past has established.
The organ by which the singing-voice is produced is the larynx. It forms
the upper extremity of the windpipe, which again is the upper portion
and beginning of the bronchial tubes, which, extending downward, branch
off from its lower part to either side of the chest and continually
subdivide until they become like little twigs, around which cluster the
constituent parts of the lungs, which form the bellows for the supply of
air necessary to the performance of vocal functions. Above, the larynx
opens into the throat and the cavities of the pharynx, mouth, nose, and
its accessory cavities, which constitute the resonator for vocal
vibrations set up within the larynx.
The larynx itself consists of a framework of cartilages joined by
elastic membranes or ligaments, and joints. These cartilages move freely
toward and upon each other by means of attached muscles. Also the larynx
as a whole can be moved in various directions by means of extrinsic
muscles joined to points above and below.
The vocal bands are two ligaments or folds of mucous membrane attached
in front to the largest cartilage of the larynx, called the thyroid, and
which forms in man the protuberance commonly called Adam's apple; and,
extending horizontally backward, are inserted posteriorly into the
arytenoid cartilages, the right vocal band into the right arytenoid
cartilage and the left band into the left cartilage. These arytenoid
cartilages, by means of an articulation or joint, move freely upon the
cricoid, the second large cartilage of the larynx, forming its base, and
sometimes called the ring cartilage, from its resemblance in shape to a
seal ring. The vocal bands are composed of numberless elastic fibres
running in part parallel to each other, and in part interwoven in
various directions with each other. The fibres also vary in length; some
are inserted into the extending projections, called processes of the
arytenoid cartilages, and some extend further back and are inserted into
the body of the cartilages. The vocal bands, then, lie opposite each
other, on a level, raised a little in front, and with a narrow slit
between, called the glottis.
The muscles controlling the action of the vocal bands, and which
regulate the mechanism producing sound, are of three groups, viz.,
abductors (drawing-apart muscles), adductors (drawing-together muscles),
and tensors.
The abductors act to keep the bands apart during respiration, while the
function of the adductors and tensors is to bring the bands into
position for speech or singing. They are, since phonation is at will,
voluntary muscles; but it is an interesting fact that the laryngeal
muscles of either side invariably act together. It has been shown that
it is not possible to move one vocal cord without the other at the same
time executing the same movement. It is thus shown that the laryngeal
muscles are, to a less extent, under the control of the will than are
those of either hand or eye. The rational training of the singing-voice
cannot, therefore, proceed upon any theory based upon the voluntary
training of the muscles controlling the movements of the vocal cords.
The mucous membrane which lines the larynx is liberally supplied with
secreting glands, whose function is to keep the parts moist. Above the
vocal bands, another pair of membranous ligaments are stretched across
the larynx forming, with its sides and the vocal bands, a pouch or
pocket. The upper ligaments are sometimes called the false vocal cords,
but are more properly termed ventricular bands. Their function has
occasioned much speculation, but whatever modification of tone they may
be supposed to produce, they no doubt protect the true vocal bands and
permit their free vibration. The larynx, in the production of sound, may
be compared to an organ-pipe. The two vocal cords which act
simultaneously and are anatomically alike, when set in vibration by the
blast of air coming from the lungs, correspond to the reed of the
organ-pipe; the vibration of the cords, producing sound, which is
communicated to the air enclosed in the cavities of the chest and head.
Pitch of tone is determined by the rapidity of vibrations of the bands,
according to acoustical law, and the length, size, and tension of the
cords will determine the number of vibrations per second, i.e., their
rapidity.
Strength or loudness of tone is determined primarily by the width or
amplitude of the vibrations of the vocal membrane, and quality or timbre
is determined by the form of the vibration.
The infinitely varying anatomical divergencies in the form and structure
of the nasal, pharyngeal and throat cavities, and possibly the
composition of the vocal bands, modifies, in numberless ways, the
character of tone in speech or song. It is a fascinating topic, but must
be dismissed here with the remark that, as those anatomical differences
in structure are far less marked in children than in adults, their
voices are, in consequence, more alike in quality and strength. It takes
long, patient training to blend adult voices, but children's voices,
when properly used, are homogeneous in tone.
The voices of boys and girls, prior to the age of puberty, are alike.
The growth of the larynx, which in each is quite rapid up to the age of
six years, then, according to all authorities with which the writer is
conversant, ceases, and the vocal bands neither lengthen nor thicken, to
any appreciable extent, before the time of change of voice, which occurs
at the age of puberty.
It is scarcely possible, however, that the larynx literally remains
unchanged through the period of the child's life, extending from the
age of six to fourteen or fifteen years. In point of fact, authorities
upon the subject refer only to the lack of growth and development in
size of the larynx during the period; but undoubtedly, during these
years, there is a constant gaining of firmness and strength, in both the
cartilages and their connecting membranes and muscles. None of the
books written upon the voice have even mentioned this most important
fact. It bears with great significance upon questions relating to the
capacities of the child's voice at different ages, and explains that
phenomenon called the "movable break," which has puzzled so many in
their investigations of the registers of the child's voice. The
constant, though of course extremely slow, hardening of the
cartilaginous portions of the larynx, and the steady increase in the
strength of its muscles and ligaments is not in the least inconsistent
with the previously noted fact, that the vocal bands during this time
increase to no appreciable extent in length; for, it may be observed,
after the change of voice, which often occurs with great rapidity, and
during which the vocal bands increase to double their previous length in
males, that, though the pitch of the voice, owing to increased length of
the bands, suddenly lowers, yet not until full maturity is reached, do
the laryngeal cartilages attain that rigidity, or the vocal bands that
ready elasticity essential to the production of pure, resonant voice.
Yet, during these years, while the voice is developing, the vocal bands
remain unchanged in length. Even in those cases where the voice
changes slowly in consequence of the slow growth in length and thickness
of the vocal cords, it takes several years, after laryngeal development
has ceased, for the voice to attain its full size and resonance.
Furthermore, the continual increase in strength and firmness of the
larynx from six years onward to puberty, is consistent with the constant
growth in strength and firmness of tissue characterizing the entire
body. It is again proven by the continual improvement in the power and
timbre of the tone through this period, always premising, be it
understood, that the voice is used properly, and never forced beyond its
natural capabilities. The voice, at the age of eleven or twelve, is far
stronger, and is capable of more sustained effort than at the age of six
or seven years, and, for the year or two preceding the break of voice,
the brilliance and power of boys' voices, especially in the higher
tones, is often phenomenal, and in all cases is far superior to that of
previous years.
The resemblance between the voices of boys and girls, a resemblance
which amounts to identity, save that the voices of boys are stronger and
more brilliant in quality, disappears at puberty.
Among the physical changes which occur at this period is a marked growth
of the larynx, sufficient to alter entirely the pitch and character of
the boy's voice. As a female larynx is affected to a lesser extent, the
voices of girls undergo little change in pitch, but become eventually
more powerful, and richer in tone.
This break of the voice, as it is called, occurs at about the age of
fifteen years in this climate, but often a year or two earlier, and not
infrequently a year or two later. The growth of the larynx goes on, with
greater or less rapidity, varying in different individuals, for from six
months to two or three years, until it attains its final size. In boys,
the larynx doubles in size, and the vocal bands increase in the
proportion of five to ten in length. This great gain in the length of
the vocal cords is due to the lateral development of the larynx, for the
male larynx, in its entirety, increases more in depth than in height.
The result is a drop of an octave in the average boy's voice, the longer
bands producing lower tones. The change in size in the female larynx is
in the proportion of five to seven, and the increase is in height
instead of depth or width as in the male larynx. The vocal cords of
women are, therefore, shorter, thinner and narrower than are those of
men.
The reason assigned for the peculiar antics of the boy's voice, during
the break, is unequal rapidity in the growth and development of the
cartilages and of the muscles of the larynx. The muscles develop more
slowly than do the cartilages, and so abnormal physical conditions
produce abnormal results in phonation.
No further changes occur in the laryngeal structure until middle life,
when ossification of the cartilages commences. The thyroid is first
affected, then the cricoid, and the arytenoids much later.
The consequent rigidity of the larynx occasions diminished compass of
the singing-voice, the notes of the upper register being the first to
disappear. In some few cases of arrested development, the voice of the
man retains the soprano compass of the boy through life.