speech sound vs linguistic unit

speech sound and linguistic unit both are nouns.

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

As nouns, linguistic unit is a hypernym of speech sound; that is, linguistic 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
linguistic unit: one of the natural units into which linguistic messages can be analyzed

Other hypernyms of speech sound include language unit.

speech sound (noun)	linguistic 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