Voice production

Quid est oratori tam necessarium quam vox?
Cicero, de Oratore, I.251

One student, exploring Caesar’s de Bello Gallico of his own accord, came across the passage where, in the course of the attack on Gergovia, some of the army got out of control, with the resultant loss of around 700 men:

Postero die Caesar contione advocata temeritatem cupiditatemque militum reprehendit, quod sibi ipsi iudicavissent quo procedendum aut quid agendum videretur, neque signo recipiendi dato constitissent neque ab tribunis militum legatisque retineri potuissent…
  Next day, Caesar called a full assembly. He reprimanded the rashness and cupidity of the soldiers, and their having judged, of their own accord, how far it seemed they should advance, or what action should be taken: they had not halted when the signal for withdrawal was given and could not be restrained by the military tribunes and the lieutenants…          de Bello Gallico, VII.51

Caesar goes on to admire their courage, and at the end of the speech urges them not to be dispirited by this reverse, nor attribute to the enemy’s courage what had been an error on their part.

The student had a question: how was Caesar able to make himself heard, on this occasion and others, to an army sometimes numbering more than 10,000 men?

Little is known about the techniques of the rhetores when they trained their pupils in voice production, by a process presumably not unlike those of singing teachers who trained voices for grand opera, in the 19th century and later.

There are hints about it in Cicero’s Brutus and de Oratore, and in Quintilian. Apparently the rhetores had liaison with Greek doctors, who advised on exercise, diet and rest; and the anatomy and mechanics of voice production were studied in detail.*  But could Julius Caesar, trained though he was in this way, make himself heard by such a number?

By chance I had come across a relevant paragraph in Benjamin Franklin’s autobiography. He says of George Whitefield, whom he heard speak in Philadelphia in 1739:

He had a loud and clear Voice, and articulated his Words and Sentences so perfectly that he might be heard and understood at a great Distance, especially as his Auditors, however numerous, observ’d the most exact Silence. He preach’d one Evening from the Top of the Court House Steps, which are in the middle of Market Street, and on the West Side of Second Street which crosses it at right angles. Both Streets were fill’d with his Hearers to a considerable Distance. Being among the hindmost in Market Street, I had the Curiosity to learn how far he could be heard, by retiring backwards down the Street towards the River; and I found his Voice distinct till I came near Front Street, when some Noise in that Street, obscur’d it. Imagining then a Semicircle, of which my Distance should be the Radius, and that it were fill’d with Auditors, to each of whom I allow’d two square feet, I computed that he might well be heard by more than Thirty Thousand. This reconcil’d me to the Newspaper Accounts of his having preach’d to 25,000 People in the Fields, and to the ancient Histories of Generals haranguing whole Armies, of which I had sometimes doubted.

*http://rh.ucpress.edu/content/ucprhet/34/2/141.full.pdf

Also of interest:
http://nationalhumanitiescenter.org/pds/becomingamer/ideas/text2/franklinwhitefield.pdf