This empty abdomen with its thoracic annex forms an enormous resonator, such as no other performer in our countryside can boast of. If I close with my finger the orifice of the truncated abdomen the sound becomes flatter, in conformity with the laws affecting musical resonators; if I fit into the aperture of the open body a tube or trumpet of paper the sound grows louder as well as deeper.
There is as yet no authoritative statement as to exactly what happens, and it is generally assumed that the effect depends on the relation of capacity to self-induction, and is a sort of resonator action. This would need a large self-induction, and a small change of speed would stop the effect. The following explanation is suggested.
To produce any kind of tone, while holding the soft palate raised, is extremely difficult. In a later chapter it will be seen that this action has no place whatever in the correct use of the voice. As the nasal cavities are fixed in size and shape, the singer cannot control or vary any influence which they may exert as a resonator.
It was formerly considered that pitch was determined solely by the rate of vibration of the vocal bands; though the author opposed this view as rigidly applied. Very recently Prof. Scripture, by the use of new methods, has shown that the supra-glottic chambers cannot be correctly likened to a resonator with rigid walls.
We know how the Bonn physicist developed, by means of oscillating electric discharges, displacement currents and induction effects in the whole of the space round the spark-gap; and how he excited by induction at some point in a wire a perturbation which afterwards is propagated along the wire, and how a resonator enabled him to detect the effect produced.
A definite location is given to the feelings, in the chest and in the head. A feeling of trembling in the upper chest is usually held to indicate that the chest cavity is working properly as a resonator. This sensation is therefore the chief reliance of most teachers in "placing" the lower tones, especially for low voices.
In the voice the exciting cause of the air vibrations is located at the back of the resonator, the mouth-pharynx cavity. The sound waves in this case can issue only from the front of the resonator, the singer's mouth. No matter how the voice is produced, correctly or badly, this acoustic principle must apply.
This is well illustrated by a simple experiment with a tuning fork and a spherical resonator reinforcing the tone of the fork. When the fork is struck, the ear hears the sound issuing from the resonator, not that coming direct from the fork. This is brought out distinctly by placing the fork at a little distance from the resonator.
All these considerations make the resonance-chambers more important than ever, so that there is greater objection to speaking of the larynx as the vocal organ than we were aware of before these investigations were undertaken. Without a resonator, which may be solid or hollow, the sound made by a reed or tense string is feeble.
Resting on the cylinder was a palladium-faced pen or spring, which was attached to a mica diaphragm in a resonator. The current passed from the main line through the pen to the chalk and to the battery. The sound-waves impinging upon the distant transmitter varied the resistance of the carbon button therein, thus causing corresponding variations in the strength of the battery current.