The following is taken from We Sang Better, Volume 2, by James Anderson, Beuthen Press, 2012.:

The older singers had a belief that if you cultivated your natural tones and your powers of musical expression, you would be able to compete with those whose voices seemed larger.

For instance, Santley said of the coloratura soprano Louisa Pyne, with whom he sang a great deal in the Pyne and Harrison Opera Company, that:

Her voice was not powerful, but it possessed that rare sympathetic quality which, developed by serious study of the art of singing, gave it the power of expansion that carried every tone, soft or loud, to all parts of the theatre.

Levien, John Mewburn. Six Sovereigns of Song. London: Novello & Company Ltd, 1948.

Pyne’s serious study, incidentally, started very young with Sir George Smart. By the age of ten, it was commented that she was easily audible over an orchestra of fifty players. We will look at the ‘power of expansion’ a little more in a moment, but J. B. Faure made much the same point:

One must consider the legato and sostenuto singing as one of the most powerful means of expression. It allows the less voluminous voice to make itself heard distinctly and even often to dominate other much stronger ones; the continuous vibrations that it communicates to the sounds tightly joined up in an invisible chain monopolise the attention of the listener and can defy the sonorities of the orchestra however intense they may be.

Faure, Jean-Baptiste, et al. La voix et le chant: traité pratique. Paris: Heugel, 1886.

This lovely description of an ‘invisible chain’ of sound was not unique to Faure. Garcia Jr in his Hints on Singing in 1894 described a similar image of chains of sound successfully reaching the ears of the audience:

Air given out in jerks does not travel. A moderate and prolonged pressure, on the contrary, gradually puts in motion the whole mass of circumambulent air; the faintest sound, given in this manner, if not drowned by accompaniment, will reach the ears of the most distant auditor.

Garcia, Manuel. Hints on singing. E. Ascherberg, 1894.

The old observation was that voices with natural tones, clear vowels and a good command of legato and sostenuto singing had the best carrying power.

Here is the composer Percy Grainger remarking that Melba’s voice was always audible, even with big orchestras:

…the curious thing with Melba was that her lower notes and middle notes were equally telling. They had a quality all of their own; and even when she was singing with a big orchestra, she was never wiped out. She had a tremendous carrying power and a tremendous beauty of tone.

Hetherington, John Aikman. Melba; a biography. Farrar, Straus & Giroux, 1968.