mutterer vs speaker

mutterer and speaker both are nouns.

Word	Noun	Adjective	Verb	Adverb
mutterer	Yes	No	No	No
speaker	Yes	No	No	No

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

mutterer: a person who speaks softly and indistinctly
speaker: someone who expresses in language; someone who talks (especially someone who delivers a public speech or someone especially garrulous)

Other hypernyms of mutterer include talker, utterer, verbaliser, verbalizer.

mutterer (noun)	speaker (noun)
a person who speaks softly and indistinctly	electro-acoustic transducer that converts electrical signals into sounds loud enough to be heard at a distance
	someone who expresses in language; someone who talks (especially someone who delivers a public speech or someone especially garrulous)