'mega phone' in Revelation 1:10

"I was in the Spirit on the Lord’s day, and I heard behind me a loud voice (phōnēn megalēn) like a trumpet ..."(Rev. 1:10)

Gk
ἐγενόμην ἐν πνεύματι ἐν τῇ κυριακῇ ἡμέρᾳ καὶ ἤκουσα ὀπίσω μου φωνὴν μεγάλην ὡς σάλπιγγος

Gk(xlit)
egenomēn en pneumati en tēi kuriakēi hēmerai, kai ēkousa opisō mou phōnēn megalēn hōs salpingos