Each one of the precepts may be said to describe some special characteristic of the perfect vocal tone, considered solely as a sound. These characteristics may each be considered separately, that is, the hearer may voluntarily pay close attention to any special aspect of the vocal tone. The best plan for arriving at the exact meaning of the precepts is therefore to consider each one in turn.
The Forward Tone
Every lover of singing is familiar with this characteristic of the perfectly produced voice; the sound seems to come directly from the singer's mouth, and gives no indication of being formed at the back of the throat. This characteristic of the perfect tone is simply heard. It is not distinguished by any sympathetic sensations, but is purely a matter of sound. On the other hand, a wrongly produced voice seems to be formed or held in the back of the singer's throat. The tones of such a voice do not come out satisfactorily; they seem to be lodged in the throat instead of at the front of the mouth.
In the badly used voice the impression of throat is conveyed by the sympathetic sensations awakened in the hearer. A striking difference between correct and incorrect singing is thus noted. A wrongly produced voice is felt by the hearer to be held in the singer's throat. When properly used the voice gives no impression of throat; it seems to have no relation to the throat, but to be formed in the front of the mouth.
So much has been written about "forward emission" that the forward characteristic of vocal tones seems to be enshrouded in mystery. As a matter of fact, the forward tone is easily explained. The perfectly produced voice issues directly from the mouth for the same reason that the tones of the trombone issue from the bell of the instrument. It is all a matter of resonance. 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. The listener can then definitely locate the source of the sound which impresses the ear. Under these circumstances the sound coming from the resonator is found to be many times more powerful than that coming direct from the tuning fork. If left to its own judgment the ear takes the resonator to be the original source of the sound.
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.
Why then does not the incorrectly used voice impress the hearer as issuing directly from the mouth, the same as the correctly produced tone? This is purely a matter of sympathetic sensations of throat tightness, awakened by the faulty tone. Every wrongly used voice arouses in the listener sympathetic sensations of throat contraction. This impression of throat, noted by the hearer, consists of muscular, not of strictly auditory sensations.
As a statement of scientific fact, the forward-tone precept is erroneous. It does not describe scientifically the difference between correct and incorrect tone-production. Correctly sung tones are not produced at the lips. Every vocal tone, good or bad, is produced by the motion of the vocal cords and reinforced by the resonance of the mouth-pharynx cavity. Only when considered as an empirical description is the forward-tone precept of value. In this sense the precept describes accurately the difference in the impressions made on the hearer by correct and incorrect singing. A badly produced tone seems to be caught in the singer's throat; the correctly used voice is free from this fault, and is therefore heard to issue directly from the singer's mouth.
This marked difference between correct and incorrect tone throws a valuable light on the meaning of the correct vocal action. Every badly used voice gives the impression of wrong or unnecessary tightness, stiffening, and contraction of the throat. When perfectly used, the voice does not convey any such impression of throat stiffness.