Institutio Oratoria

Delivery will be ornate when it is supported by a voice that is easy, strong, rich, flexible, firm, sweet, enduring, resonant, pure, carrying far and penetrating the ear (for there is a type of voice which impresses the hearing not by its volume, but by its peculiar quality): in addition, the voice must be easily managed and must possess all the necessary inflexions and modulations, in fact it must, as the saying is, be a perfect instrument, equipped with every stop: further, it must have strong lungs to sustain it, and ample breathing power that will be equal to all demands upon it, however fatiguing.

The deepest bass and the highest treble notes are unsuited to oratory: for the former lack clearness and, owing to their excessive fullness, have no emotional power, while the latter are too thin and, owing to excess of clearness, give an impression of extravagance and are incompatible with the inflexions demanded by delivery and place too great a strain upon the voice.