The engineer of a great pumping station once told me that his mammoth Corliss engine was so perfectly balanced that he could run it with ten pounds of steam. When the voice is free, and resting on the breath as it were, it seems to sing itself.
An illustration of the opposite condition, of extreme resistance was once told me by the president of a great street railway system that was operated by a cable. He said it required eighty-five percent of the power generated to start the machinery, that is, to overcome the resistance, leaving but fifteen percent for operating cars. It is not at all uncommon to hear singers who are so filled with resistance that it requires all of their available energy to make the vocal instrument produce tone. Such singers soon find themselves exhausted and the voice tired and husky. It is this type of voice production rather than climatic conditions,that causes so much chronic laryngitis among singers. I have seen the truth of this statement verified in the complete and permanent disappearance of many cases of laryngitis through learning to produce the voice correctly.
Clippinger, David Alva. The head voice and other problems: Practical talks on singing. Oliver Ditson Company, 1917.