chest register vs chest voice

chest register and chest voice both are nouns.

Word	Noun	Adjective	Verb	Adverb
chest register	Yes	No	No	No
chest voice	Yes	No	No	No

As nouns, chest register and chest voice are synonyms defined as:

chest register and chest voice: the lower ranges of the voice in speaking or singing

Other synonyms of chest register include chest tone.

chest register (noun)	chest voice (noun)
the lower ranges of the voice in speaking or singing	the lower ranges of the voice in speaking or singing