megaphone vs acoustic device

megaphone and acoustic device both are nouns.

Word	Noun	Adjective	Verb	Adverb
megaphone	Yes	No	No	No
acoustic device	Yes	No	No	No

As nouns, acoustic device is a hypernym of megaphone; that is, acoustic device is a word with a broader meaning than megaphone:

megaphone: a cone-shaped acoustic device held to the mouth to intensify and direct the human voice
acoustic device: a device for amplifying or transmitting sound

megaphone (noun)	acoustic device (noun)
a cone-shaped acoustic device held to the mouth to intensify and direct the human voice	a device for amplifying or transmitting sound