The adjective stentorian describes a booming voice. If you're teaching a group of unruly kids, you'll need to practice a stentorian voice to be heard above the din.
The adjective stentorian comes from Greek mythology. Stentor was a herald in the Trojan War, mentioned in Homer's "Iliad." Homer wrote of brazen-voiced Stentor, whose cry was as loud as that of fifty men together. So anyone with a stentorian voice has a voice like the mythic Stentor. You can also use stentorian to describe a style of speaking that emphasizes boom and power.