Tone is the product of the whole resonator, which comprises three resonant spaces, the neck, the mouth and the nose.

That in the neck is the most important for "tone" and general quality, the mouth for vowel quality and the nose a powerful accessory to be added in due proportion.

Below the larynx, i.e. windpipe and lung cavities, there is no proper resonation, but some vibration transmitted through the air and through the attachment of the larynx to the breast-bone.

Tone may be defined as resonance within certain limited spaces. We must consider what those spaces are. There is a large space in the mouth, the space behind the uvula, and (most important of all from an individual characteristic point of view) the nasal cavity. In addition to these, there is the big tube below the larynx that runs right down to the lower depths, and of course there are the big spaces in the chest. Now, resonance being the thing we are aiming at, it follows that the bigger the spaces are the more resonance we shall get, provided we use those spaces. Therefore have the mouth as wide open as it can be with comfort, not stretched open but just easily wide open. The cheeks should be high (as in smiling), as this brings them away from the side teeth, thus increasing the width of the cavity, besides which it makes the singer look happy. You will never get a bright tone with a dull face.

At the same time it is necessary and advisable to warn students against wearing a perpetual smile. It kills most of the vowels and stiffens the jaw. Freedom and looseness are equally necessary in both joy and sorrow.

The space behind the uvula should be wide and gaping, but not stiff. The larynx as low as it can go and loose too (which it will be if the breath is taken correctly). It is unconsciously drawn downwards and forwards in relation to the sense of expansion, and is adjusted to the needs of every vowel position. It is drawn up in the guttural consonants K and G.

As the voice ascends in the scale the larynx must not be allowed to rise up, as it will often want to do, but must remain low and loose exactly the same for the high notes as for the low ones. The tongue should lie flat and limp and forward on the floor of the mouth. The lower jaw should hang quite freely without the smallest feeling of tightness.

The spaces in the mouth and behind the uvula can by these means be enlarged to their utmost. "Gaping" is the right word. When you sit on the edge of your bed and revel in your first great morning yawn, your throat is in just the right position for singing.

Now, it will be obvious to everyone that those two spaces can be enlarged. We cannot enlarge either the big tube or the nasal cavity, but we can use them.

There is nothing that will add character and individuality to the voice so much as the proper use of the nasal cavity. It must, of course, be used with discretion. It is all a question of balance. The larger you make your other spaces the more you can use your nose. There is a vast difference between a nasal and a nosey tone. The one is beautiful, the other is not. The use of the nasal cavity is like the pinch of salt in the soup. Without it the finest soup will taste insipid.

Why is it, do you think, that if you hear twenty throaty tenors sing they all sound alike? It is not only caused by their contracting or closing their throats but to a very great extent because they don't use their noses. You can quite easily proves this by experiment. So, when you are teaching tone production, you must see to it that all the spaces are used in their proper balance for the purpose of obtaining the necessary resonance, and it follows that the more you use the back spaces the more you can use the nasal cavity.

Remember that tone comes from below and must be focussed in the front of the mouth where it going forces with articulation.

You will find that nearly every new pupil that comes to you will sing almost entirely at the back of the mouth. This is to a great extent caused by our damp climate. It doesn't happen in Italy. Nearly all the throats are wide open there. It is a fault that must be cured at once. Usually the root of the tongue will be clogging up the space behind it, and the cure for it is to being that unruly member forward and let it rest peacefully and flat on the floor of the mouth. It must not be stiffened, for, if it is, the lower jaw will be stiff too, and vise versa. The thing to be achieved is to bring the tone to the front of the mouth. It is quite obvious why this is essential. Singing is glorified speech. We speak on our lips and in the front of the mouth. Nearly all the consonants live there. If the voice is at the back and the speech is at the front the one is pulling against the other all the time and the result is a continual struggle. Get the student to say the syllables la, na, ta, da, and get get him to notice what part of the hard palate the tip of the tongue touches for all these consonants. It is just over the teeth. Call that the target, aim the focus of the tone at it and score bull's-eye every shot. Every note that we sing, high or low, loud or soft, must be kept focussed on that spot and must not be allowed to be back on to the soft palate. It will go back if you let it, but you mustn't let it. If you do away goes your tone-colour and you won't be able to get it back again until something drastic, such as a forte or a fresh breath (and consequently a fresh start), comes to the rescue.

Remember that all the bright tone-colours are in the front of the mouth. You need not bother much about the dull colours. It is easy to be dull.

Many people approach the act of singing as a tremendous business. It is quite a usual thing to see a singer walk to the piano in a perfectly easy, natural and graceful manner, and then, just before the song begins, the body stiffens, the arms become rigid, the hand, perhaps, clenched tightly, the face and jaw and throat and the whole box of tricks become set fast, a frown makes its appearance, and a look of dull solemnity takes at the place of the bright and natural smile. The singer is making the awful, though silent, announcement, "Ladies and Gentlemen. I am about to sing." Why all that fuss? How much better it would be if he would retain his natural ease and attitude, and simply open his mouth and sing. The eased naturalness of the performance is half the battle, and the message of the song will go straight to the hearts of the listeners if it is unhampered by a whole cargo of unnecessary contortions, all of which are detrimental to the production of a beautiful tone. The tone must flow out in a continual stream, just touching the consonants on its way, not stopping it but touching them as it passes, unimpeded either by them or by anything else. It must be like a man walking past a series of posts and tapping them as he proceeds, his movements not being impeded, but in fact enhanced and embellished by the act. So it must be with the outward flow to tone.

You will find that many students will stop the flow of the tone immediately they come against a consonant, obviously separating the one from the other. Try to get them to weld them together and take the tone through the consonant whenever possible.

Having achieved beauty of tone, the next thing must be to enlarge it to it utmost. This will be done by the use of the crescendo on single sustained notes, beginning always in the middle of the voice (say A natural) and working downwards to, say, E natural, then starting again a note higher than before and working downwards again, and so on. The crescendo should be maintained on each note as long as the beauty of the tone remains unimpaired. The moment the smallest sign of strain of forcing appears, the pupil must stop and begin a new note. There must not be the slightest alternation or movement of any part of the vocal instrument at any time during the crescendo.

Try to make the student realize what he is doing, and that he must feel as if it is all coming from below and focusing in the front of his mouth. Sometimes he will feel something in the region of his diaphragm, but he should feel absolutely nothing in his throat. If he has those sensations at the bottom of his big tube and in the neighborhood of his front teeth and nowhere else, he will be will on the way to mastering the art of tone production. These rules apply to his loudest forte and his softest piano as well as to all intermediate stages. Never cease to impress on him the fact that if he feels any sensation in his throat he is doing something wrong.

—Harry Gregory Hast, "Placing the Tone," The Singer's Art (1925): 13-18.

Harry Gregory Hast (1856-1944) made his first appearance on these pages in 2009. Unfortunately, then as now, his book is not available for download. However, having been published in 1925, the likelihood that The Singer's Art is now in the public domain is strong since British copyright law, which extends 50 to 70 years after the death of an author, places the outer limit for Hast's book in 2014.

The passage above contains some of the most cogent instructions that I have encountered. Find the book if you can.