tweeter vs speaker unit

tweeter and speaker unit both are nouns.

Word	Noun	Adjective	Verb	Adverb
tweeter	Yes	No	No	No
speaker unit	Yes	No	No	No

As nouns, speaker unit is a hypernym of tweeter; that is, speaker unit is a word with a broader meaning than tweeter:

tweeter: a loudspeaker that reproduces higher audio frequency sounds
speaker unit: electro-acoustic transducer that converts electrical signals into sounds loud enough to be heard at a distance

Other hypernyms of tweeter include loudspeaker, loudspeaker system, speaker, speaker system.

tweeter (noun)	speaker unit (noun)
a loudspeaker that reproduces higher audio frequency sounds	electro-acoustic transducer that converts electrical signals into sounds loud enough to be heard at a distance