B vs sound unit

B and sound unit both are nouns.

Word	Noun	Adjective	Verb	Adverb
B	Yes	No	No	No
sound unit	Yes	No	No	No

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

B (noun)	sound unit (noun)
aerobic rod-shaped spore-producing bacterium; often occurring in chainlike formations; found primarily in soil	any acoustic unit of measurement
the blood group whose red cells carry the B antigen
the 2nd letter of the Roman alphabet
a logarithmic unit of sound intensity equal to 10 decibels
a trivalent metalloid element; occurs both in a hard black crystal and in the form of a yellow or brown powder
originally thought to be a single vitamin but now separated into several B vitamins