central vowel vs vowel sound

central vowel and vowel sound both are nouns.

Word	Noun	Adjective	Verb	Adverb
central vowel	Yes	No	No	No
vowel sound	Yes	No	No	No

As nouns, vowel sound is a hypernym of central vowel; that is, vowel sound is a word with a broader meaning than central vowel:

central vowel: (linguistics) any vowel sound in which the tongue is positioned halfway between a front vowel and a back vowel.
vowel sound: a speech sound made with the vocal tract open

Other hypernyms of central vowel include vowel.

central vowel (noun)	vowel sound (noun)
(linguistics) any vowel sound in which the tongue is positioned halfway between a front vowel and a back vowel.	a speech sound made with the vocal tract open