vox vs singing voice

vox and singing voice both are nouns.

Word	Noun	Adjective	Verb	Adverb
vox	Yes	No	No	No
singing voice	Yes	No	No	No

As nouns, singing voice is a hyponym of vox; that is, singing voice is a word with a more specific, narrower meaning than vox:

vox: the sound made by the vibration of vocal folds modified by the resonance of the vocal tract
singing voice: the musical quality of the voice while singing

Other hyponyms of vox include sprechgesang, sprechstimme, voice over, voice.

vox (noun)	singing voice (noun)
the sound made by the vibration of vocal folds modified by the resonance of the vocal tract	the musical quality of the voice while singing