Dudley Buck, Jr. (son of the well-known American composer Dudley Buck), devoted his life to the study of vocal problems, and his opportunities for research both in the US and in Europe were very extensive.
From the Etude Magazine again, his thoughts and the results of his practical experience will be covered in several posts on this blog:
Nature shows us at once that the overtone has much the better carrying power. Imagine that you were calling to a friend a long way off, and see what will happen. The should will be thrown up into the head, and the overtone will appear at once leaving no strain upon the throat. The “Coo Hoo” call of children is also always given in overtones proving again the carrying thought. In the early age of song, most of which was heard in the churches, the compass of different voices was quite different from that of to-day. For instance, the soprano never sang above F or F#, the alto perhaps to C, the tenor to E or F, and the bass to C or D, showing conclusively that only the tones of the true voice, or more commonly known as the chest voice, were used. Suddenly we find the compass of all compositions change. The soprano parts being written up as high as C, the altos to F or G, the tenors to A and B and the basses to F, unquestionably due to the discovery of the falsetto or head voice.
The wise old Italian masters not only had wonderful hearing but were much more scientific than the majority of teachers to-day. They produced voices of wonderful beauty, of great compass and of remarkable agility. This was the result of scientifically reinforcing overtones so that the voice not only extended in compass and in beauty of tone, but became even throughout its entire range, and was always in a position to move, in the overtone, to any part of its compass with great facility. Thus the jump of an octave, or even a tenth, was conquered as easily as that of a third or a fifth. I can do no better than reiterate that a tone minus its harmonics or overtones is of little value.
The foregoing is especially applicable to the head voice, the most valued possession of all singer. There is not the slightest doubt but that a mechanical change does occur in the upper range of all voices. Gray, who is certainly one of the greatest authorities on anatomy, says that everybody has two sets of vocal chords, the one fibrous and the other mucous. It is therefore, readily to be seen that after the fibrous chords (the true chords) have been vibrated to their utmost tension some mechanical change must occur to obtain the high notes. This change consists of substituting the mucous chords (the false chords) for the fibrous ones, and as the larynx relaxes, the tone is thereby produced with much less tension and effort. People scoff at a falsetto tone, saying “do not use it, it will injure your voice,” but the fact remains, nevertheless, that the high notes of all voices are but reinforced falsetto or head tones, and furthermore, that the action of the larynx is as natural in producing the falsetto tone, as it is in producing the the true tone.