I thought Charles Kullman should appear again since I referenced him in my post on Lanny Ross a few days ago. Both tenors studied at Yale, sang in the glee club, and were students of Anna E. Schoen-René at the Juilliard School.
One has the distinct impression when listening to Kullman that he didn't have a big voice, but rather, knew- or was taught- how to make the most of what he had. I am thinking the latter! His vocal production is unforced, yet quite resonant.
Legion are the singers who strain to sing repertoire that is more dramatic than the voice can withstand, yet, upon hearing Kullman, one has the sense that he knew where the cliff was. That comes with expert training which he seems to have have gotten under the tutelage of Schoen-René. Of course, I am harping when I mention (yet again) that students of Kullman's generation were made to develop vocal technique for at least two semesters before they were allowed to sing repertoire. Vocal training was systematic in nature, progressively difficult and unrelenting. Students learned to create - among many things- a beautiful tone with full voice, then mezza voce, decrescendo and crescrendo, trills, and finally, the messa di voce- all with clear unobstructed vowels. Force was not a consideration.
It took a heck of a lot of work.