RESONANCE IN GENERAL
The intimate relationship existing between voice culture and the
science of acoustics was formerly slightly perceived. The teaching of
singing, as an art, then rested altogether on an empirical basis, and
the acoustics of singing had not received the attention of scientists.
With the publication in 1863 of Helmholtz's great work[4] a new era
began, although singer and scientist yet continue to look upon each
other with suspicion. Teachers of the voice, casting about for a
scientific basis for their work, were greatly impressed with
Helmholtz's revelations in regard to vocal resonance--the fact that
tones are modified in quality as well as increased in power by the
resonance of the air in the cavities of pharynx and head.
[Footnote 4: _Die Lehre von den Tonempfindungen als physiologische
Grundlage für die Theorie der Musik._ (The Sensations of Tone as a
Physiological Basis for the Theory of Music.)]
Writing in 1886, Edmund J. Meyer speaks of the importance of a "study
of the influence of the different resonance cavities as the voice is
colored by one or the other, and the tuning each to each and each to
all"; yet, he adds, "the subject is seldom heard of outside of books."
The basic importance of resonance in the use of the voice is still too
little recognized, though obvious enough in the construction of
musical instruments. With the exception of a few instruments of
percussion, all musical instruments possess three elements,--a
_motor_, a _vibrator_, and a _resonator_. The violin has the moving
bow for a motor, the strings for a vibrator, and the hollow body for a
resonator. The French horn has the lungs of the performer for a motor,
the lips for a vibrator, and the gradually enlarging tube, terminating
in the flaring bell, for a resonator. In the pianoforte the
hammer-stroke, the strings, and the sounding-board perform the
corresponding offices. Though improvements in other parts of the piano
have done much to increase the volume of the tone, yet in the radical
change of form, size, and other physical qualities of the
sounding-board consists the evolution of the modern pianoforte from
the primitive clavichord.
In all these instruments the quality and power of the tone depend upon
the presence of these three elements,--the perfection of their
construction, their proper relation as to size and position, and the
perfect adaptation of each part. A split sounding-board spoils the
pianoforte, the indented bell destroys the sweet tone of the French
horn, and a cracked fiddle is the synonym for pandemonium itself.
The quality and power of resonance is well illustrated by a
tuning-fork, which, if set in vibration, can, unaided, scarcely be
heard by the person holding it. But if rested on a table, or a plate
of glass, or, better still, on the bridge of a violin, its tones may
be distinctly heard throughout a large hall.
The vibrating violin string when detached from the body of this
instrument, although attuned to pitch, gives absolutely no musical
sound; the lips of the player placed on the mouthpiece detached from
the tube and bell of the brass instrument produce only a splutter; and
a pianoforte without a sounding-board is nil. The air column in the
tube of the French horn, and the sounding-board of the pianoforte
develop the vibrations caused by the lips and strings into musical
tones pleasing to the ear. The tuning-fork alone can scarcely be
heard, while the induced vibrations it sets up through properly
adjusted resonance may be audible far away.
The vocal cords alone cannot make music any more than can the lips of
the cornet player apart from his instrument. _The tone produced by the
vibrations alone of the two very small vocal bands must, in the nature
of things, be very feeble._
Ninety-and-nine persons if asked the question, what produces tone in
the human-voice, would reply, "the vibrations of the vocal cords,"
and stop there, as if that were all; whereas the answer is very
incomplete--not even half an answer.
A great deal of the irrational and injurious "teaching" of singing
that prevails everywhere, and of the controversy that befogs the
subject, is due to the widely prevalent notion that the little vocal
cords are the principal cause of tone, whereas they are in themselves
insignificant as sound producers.
=It is the vibrations of the air in the resonance chambers of the human
instrument, together with the induced vibrations of the instrument
itself, which give tone its sonority, its reach, its color, and
emotional power.=
That this is not an empirical statement but a scientific fact, a few
simple experiments will demonstrate.
Tone, in the musical sense, is the result of rapid periodic vibration.
The pitch of tone depends upon the _number_ of vibrations in a given
period; the loudness of tone depends upon the _amplitude_ of the
vibrations; the quality of tone depends upon the _form_ of the
vibrations; and the form of the vibrations depends upon the
_resonator_.
The fact that pure white light is a compound of all the tints of the
rainbow into which it may be resolved by the prism is well known, but
the analogous fact that a pure musical tone is a compound of tones of
different rates of vibration, tones of different pitch, is not so much
a matter of common knowledge, and not so obvious.
Analysis shows that a musical tone consists of a fundamental note and
a series of overtones.[5] The ear is quite capable of recognizing many
of these overtones and may be trained to do so. The most obvious can
be readily separated from a fundamental by a simple experiment.
[Footnote 5: For fuller exposition see Tyndall on _Sound_, or the
section devoted to _Acoustics_ in any text-book on Physics.]
The overtones arrange themselves in a definite order, as follows: (1)
the fundamental or prime tone; (2) an overtone one octave above the
fundamental; (3) an overtone a fifth above No. 2; (4) an overtone a
fourth above No. 3 (two octaves above the fundamental); (5) an
overtone a major third above No. 4; (6) an overtone a minor third
above No. 5. There are others in still higher range but those
indicated are easily demonstrated on the piano. For C they would be as
follows:
[Music illustration]
Experiment I
Step to your piano, noiselessly press and hold down the key of No. 2,
then strike the fundamental No. 1, with force and immediately release
it. As a result No. 2 will sound clearly, and if your ears are keen
you will at the same time hear No. 6. In succession hold down the keys
of 3, 4, 5, and 6, while you strike and release the fundamental No. 1.
If your piano is "in tune" you will probably hear No. 6 when holding
the key of any other note of the series.
In a musical tone of rich quality the overtones just indicated are
present in their fulness, while tone that is weak and thin is made so
by the absence or weakness of the overtones. I have stated that the
quality of a tone depends on the _form_ of its vibrations, and that
the form of its vibrations is determined by the character of the
_resonator_. We can now amplify this by saying that while the relative
presence or absence of overtones determines the clang or color of a
tone, their presence or absence is determined by the _character of the
resonance_.
An English writer records that he was once in the garden at the back
of a house while a gentleman was singing in the drawing-room. The
tone-quality was good, and the pitch so unusually high he hastened to
learn who sang tenor high C so beautifully. On entering the room,
instead of the tenor he had supposed, he found the singer was a
baritone, and the note sung was only middle C. The fundamental tone
had not reached him in the garden but the first overtone, an octave
above it, had. Concrete illustrations will make the subject still
clearer.
Experiment II
If an ordinary tuning-fork when vibrating is held in the hand its
intrinsic tone is too weak to carry far. Rest the handle of the
vibrating fork on a bare table or the panel of the door, and the sound
is greatly augmented. _The vibrations of the fork have by contact
induced similar vibrations in the wooden table or panel which
reinforce the primary tone._
Experiment III
Place the handle of the vibrating tuning-fork on a small upturned
empty box, or, better still, in contact with the body of a violin, and
the sound will be stronger than in the previous experiment, because to
the vibrations of the wood are added the vibrations of the air
enclosed in the box or the violin. _To the resonance of the wood has
been added the sympathetic resonance of the confined air._
Experiment IV
Hold the vibrating fork over the mouth of an empty fruit-jar and there
will probably be little or no reinforcement; but gently pour in water,
thereby shortening the air column within the jar, and the sound of the
fork will be gradually intensified until at a certain point it becomes
quite loud. If you pour in still more water the sound will gradually
become feebler. This shows that _for every tone an air column of a
certain size most powerfully reinforces that tone_.
Experiment V
As a sequence to the last experiment, take two fruit-jars of the same
size, and, having learned to what point to fill them for the greatest
resonance, fill one jar (after warming it) to the required point with
hot water, the other with cold water, and you will find that the
resonance of the heated, therefore expanded, air is much less than the
denser air of the cold jar. This shows that _the degree of density of
the air affects its resonance_.
Experiment VI
To demonstrate the resonance of the oral cavity, apart from the voice,
hold a vibrating tuning-fork before the open mouth. Vary the shape and
size of the cavity until the sound of the fork suddenly increases in
volume, showing that the right adjustment for resonance has been made.
_This intensification of the sound is due to the vibration of the air
in the mouth cavity, together with the sympathetic vibration of the
surrounding walls._
Experiment VII
As an illustration of sympathetic resonance without contact, sing
forcibly a tone that is within easy range, and at the same time
silently hold down the corresponding key of the piano. On ceasing to
sing you will hear the tone sounding in the piano. This may be further
illustrated by playing on the open string of one violin while another,
tuned to the same pitch, rests untouched near by. Through _sympathetic
resonance_ the corresponding string of the second violin will vibrate
and sound its note. The louder the first violin is played the louder
will be the sympathetic tone of the second.
The deep pedal-tones of a church organ often induce sympathetic
resonance that may be felt beneath the feet of the listener. One
writer, a singer, speaks of living in the same house with two
deaf-mutes. He lodged on the first floor, they on the third. One day,
meeting at luncheon, one of the deaf-mutes told the singer that he had
begun practice earlier that morning than usual. Surprised, the writer
asked how he knew. The deaf-mute replied that they always knew when he
was singing because they felt the floor of their room vibrate.
If tone vibrations can be transmitted so readily throughout a house,
it is not difficult to understand how easily the vibrations of bone
and tissue can be transmitted until the whole framework of the body
responds in perceptible vibration.
It is said that Pascal at the age of twelve wrote a dissertation on
acoustics suggested by his childish discovery that when a metal dish
was struck by a knife the resulting sound could be stopped by touching
the vibrating dish with a finger.
With this in mind it is not difficult to understand how compression of
the human instrument by the pressure of tight clothing without, or by
false muscular tension within, must interfere with its free vibration
and so rob the produced tone of just so much of perfection.
From these experiments we can understand that, while the tones of the
voice are initiated by or at the vocal cords, the volume and character
of the tones are dependent upon _resonance_,--the vibration of the air
in the various resonance chambers of the body, together with the
sympathetic vibration of the walls of these chambers and the bony
framework that supports them.
In respect to resonance, as in other respects, the human voice is far
superior to all other instruments, for their resonators are fixed and
unchanging, while the human resonator is flexible,--in Helmholtz's
words "admits of much variety of form, so that many more qualities of
tone can be thus produced than on any instrument of artificial
construction."
We are now prepared to realize the error of the common notion that
loudness of tone is due entirely to increase of breath pressure on the
vocal cords. Simple experiments with the tuning-fork have shown that
while the volume of sound it gives forth is due in part to the
amplitude of its vibrations, its loudness is _chiefly_ due to the
character of the _resonance_ provided for it.
The larger the resonance chamber the greater is its reinforcing
capacity. The largest air chamber in the body is the chest, which
serves not only as a wind-chest, but as a resonance chamber. The
necessity for chest expansion, therefore, is not, as generally
supposed, merely for air, but to increase its size as a resonance
chamber.
In view of the laws of tone, how great is the common error of speaking
of the larynx as if it alone were the vocal organ, when the principal
vibrations are _above_ the vocal cords in the chambers of _resonance_!
Since the musical value, the beauty of tone, as well as its volume,
comes only from right use of the resonator, our principal business
must be the acquiring control of the vibratory air current _above the
larynx_. The acquirement of this control involves the proper focusing
or placing of the tone, with the free uncramped use of all the vocal
organs; power will then take care of itself.