speech sound vs language unit

speech sound and language unit both are nouns.

Word	Noun	Adjective	Verb	Adverb
speech sound	Yes	No	No	No
language unit	Yes	No	No	No

As nouns, language unit is a hypernym of speech sound; that is, language unit is a word with a broader meaning than speech sound:

speech sound: (phonetics) an individual sound unit of speech without concern as to whether or not it is a phoneme of some language
language unit: one of the natural units into which linguistic messages can be analyzed

Other hypernyms of speech sound include linguistic unit.

speech sound (noun)	language unit (noun)
(phonetics) an individual sound unit of speech without concern as to whether or not it is a phoneme of some language	one of the natural units into which linguistic messages can be analyzed