He speaks in a stentorian voice
Nouns often have the potentiality to generate adjectives that express a particular attribute of the character of the person designated by that name.
So for example we speak about a "platonic love" with an adjective derived from the name of the famous Greek philosopher Plato, to describe a love that moves it self in the plane of the ideas but not on the physical plane of pure matter and corporeality.
See this blog article referred to the terms "Apollonian" and "Dionysian" , adjectives derived respectively from Apollo and Dionysus http://en.antiquitatem.com/apollonian-dionysian-nietzsche-apollo .
Modernly an adjective that has had remarkable fortune has been "Kafkaesque" to describe situations, especially administrative, in which, by absurd, there is a lack of logic.
"Stentorian" is an adjective that applies only to the noun "voice" or synonyms. The Royal Spanish Academy (Real Academia Española, RAE) defines it as "applied to the voice or accent: Very strong, loud or boomy" and the “Spanish use Dictionary” of Maria Moliner defines it as "Applied to voice, shout or very powerful sound emitted by a person or an animal. "
It comes from the Latin Stentoreus and this from Greek adjective Στεντόρειος and this one from Στέντωρ 'Stentor', one of the Greeks in the Iliad known for his strong voice. The Latin dictionaries usually define it as "that belonging to Stentor or to very loud voice."
Certainly Stentor is a character in the Iliad. Homer says in Iliad V 784-786:
“there Hera stood still and raised a shout like that of brazen-voiced Stentor, whose cry was as loud as that of fifty men together”.
ἔνθα στᾶσ᾽ ἤϋσε θεὰ λευκώλενος Ἥρη
Στέντορι εἰσαμένη μεγαλήτορι χαλκεοφώνωι,
ὃς τόσον αὐδήσασχ᾽ ὅσον ἄλλοι πεντήκοντα·
The term or figure of Stentor became proverbial already in ancient times. Aristotle, in his "Politics", offers a city of such size that citizens can meet face each other, because if the city was very large would be very difficult for someone could be the boss; and says in Book VII, 1326b:
“for who will command its over-swollen multitude in war? or who will serve as its herald, unless he have the lungs of a Stentor?”
τίς γὰρ στρατηγὸς ἔσται τοῦ λίαν ὑπερβάλλοντος πλήθους, ἢ τίς κῆρυξ μὴ Στεντόρειος;
In Latin, for example, Juvenal refers to him in Satire XIII, v.112
“but you, poor wretch, may shout so as to out-do Stentor,
or rather as loudly as the Mars of Homer”,
tu miser exclamas, ut Stentora uincere possis,
uel potius quantum Gradiuus Homericus:
The name “Stentor”seems to come from the Indo-European root * (s) ten-which means “to scream”; in Greek στένω, steno, means "moan, complain, sigh, whine".