First, freedom of voice is attained (technically speaking) by right direction of tone and vital support. A few words of explanation will make this patent.
If the vibrating column of air when it leaves the vocal cords is so directed that it passes freely through all the cavities of resonance, it cannot fail to find the right one. The following exercise, if properly taken, will induce right direction of tone: produce a light humming sound such as would be the sound of m, n, or ng, if so idealized as to eliminate that element of sound commonly spoken of as nasality. That which is called nasality is caused by the failure of the tone to reach freely the anterior cavities of the nares. The cavity which lies just back of the nose and frontal bone imparts a musical resonance resembling the vibrating after-tone when a note has been struck upon a piano and allowed to die away gradually. The "nasal" effect comes when the tone is confined in the posterior or back part of the nares, or head cavity, or is split by the dropping of the uvula so that part of the tone is directed through the nares and part through the mouth. Many so-called "humming tones" are given for practice, but in accepting them observe whether the foregoing principle is obeyed.
The controlling center of consciousness is the extreme limit of the nares anteri. The tone should be thought of as outside. Keep the mind upon results, just as one would hold the thought of a certain figure which one might desire to draw. If one wishes to inscribe a curve, he thinks of the curve as an object of thought, not of the muscles which act in executing it. So with the voice. A tone is not a reality until its form of vibration reaches the outer air. One should always think of the tone one wishes to make—never listen to one's own execution. If the ideal is not reached by the effort it will be known by the sense of incompleteness.
Why is the nares anteri the ruling center of tone direction? The dominant or ruling center of any organism is that point which, if controlled, will involve the regulation of all that is subordinate to it. For example, the heart is the dominant center of the circulatory system; the brain is the dominant center of the nervous system; the sun is the dominant center of the planetary system. In all these systems, if the center be affected, the system is proportionately influenced. If any other part than the dominant center be affected, it is true that all other parts may also be affected, but the desired unity in result will not be secured.
The voice will follow the thought as surely as the hand will reach the object aimed at. The extreme anterior part of the nares, or head cavity, is the chamber of resonance farthest from the vocal cords. Therefore, if the voice be directed through that chamber of resonance all the others must be passed in reaching it, and hence all must be accessible to the vibrating column of air. It is a law of acoustics that any given cavity of resonance will resound to that pitch to which its size corresponds, and to no other. This law of sound secures the appropriate resonance for every pitch much more accurately than it could be secured by an effort to develop chest, middle, and head registers through calculating the differences. Again, we need the higher chambers of resonance to reinforce even the low pitch, because every note has its overtones that enrich it, and if these cannot find their proper resonance the tone is impoverished. It may be well to explain our use of the term "overtone."
This word "overtone" is used unscientifically by many. The significance of its use is somewhat varied among teachers, but it generally means head resonance, or a tone "sent over" through the head cavities. The term is used here technically, not arbitrarily. Overtones are not confined to the voice, but are those constituent parts of any tone which are produced by the vibrating segments into which any vibrating cord will divide itself.
Any cord, or string, stretched between two given points, when struck will vibrate throughout its entire length in waves of a certain length and with a certain degree of rapidity, according to the tension of the string. This vibration of the entire length of cord gives forth the tone heard as the fundamental pitch or tone. Besides this fundamental or primary vibration, the movement divides itself into segments, or sections, of the entire length. These sections also have vibrations of their own which are of shorter length and more rapid motion. The note given off by these subdivisions is, of course, on a higher pitch than that produced by the fundamental vibration of the cord; hence, they are higher tones, or overtones. It will be remembered that pitch depends upon the rapidity of the sound waves or vibrations. This subdivision of the vibrations is incalculably multiplied, so that it may be said to be impossible to determine the number of overtones accompanying the fundamental tone. What the ear hears is the fundamental pitch only; the overtones harmonize with the primary or fundamental tone, and enrich it. Since this is a law of vibration, it is unscientific to speak of giving an overtone, for all tones contain overtones. Where these overtones are interfered with by any imperfection in the instrument the result is a harsh or imperfect sound.
In relation to the voice it should now be clearly understood that since it is the overtones which enrich or give a harmonious sound to any tone, and since all tones (low as well as high) have overtones as constituent parts of their being, therefore the whole range of the resonant cavities of the voice should, for the production of pure tone, be open to all degrees of pitch, in order that the overtones may find their appropriate reinforcement in the resonance chambers. Thus the quality of the voice depends, not simply upon the condition of the vocal cords themselves, but upon the form and quality of the resounding cavities.