Many commentators have puzzled over the extent of ἄποπτος --- that is, they have wondered whether Athena is visible to the audience or if she instead makes her comment from off-stage.

All commentators except Campbell gloss on this line.

The primary meaning of κώδων is bell, but it means also bell of the trumpet as is the case here (Hermann, p. 11, Kamerbeek and Finglass; for examples of both meanings of the word see Finglass ad loc.). As reflected in the translations, the use of κώδων to mean salpinx is a synecdoche (pars pro toto):

• "like that of a bronze-mouthed Etruscan trumpet" (Finglass)
• "la trompette tyrrhénienne à la bouche de bronze" (Demont, de Romilly)
• "le clairon étrusque au pavillon d'airain" (Mazon)
• "tromba dalla bronzea bocca" (Untersteiner)
• "come di tirrenea bronzea tromba" (Ferrari)

As observed by Stanford ad loc., the assonance caused by the repetition of the ο and ω sounds makes for a "fine, loftily phrased, resonant line suggesting the grandiose style of Sophocles' Aeschylean period". When constructing the sentence, φώνημα should be supplied, to which the genitive refers: Εὐμαθὲς ὡς (φώνημα) κώδωνος (Tournier, p. 8), and ὡς (φώνημα) κώδωνος (Wecklein).

The simile echoed here is the one at Hom. Il. 18.219-222 where the cry of war of Achilles – whose crying is joined by Athena – is likened to the ἀριζήλη φωνή of the σάλπιγξ. This assonance is, perhaps, the reason why Sophocles chose κώδων over σάλπιγξ. While cited cursorily already by Schneidewin and Wecklein, the first to give this Homeric parallel the importance it deserves was Jebb (p. 14).

By comparing Athena's voice to the sound of a "bronze-mouthed Etruscan trumpet", Sophocles probably intended to emphasise its loudness: "Die erschütternde und das Herz erbeben machende Stimme der Göttin", as Wecklein aptly noted. The salpinx, whose sound could be heard at remarkable distances, was used in the Classical period not only in the context of war but also to signal the beginning/end of assemblies or theatre performances (Spineto 2005), as well as in the cult (on this specific aspect, see (Nordquist 1996)).