quadraphony vs stereo system

quadraphony and stereo system both are nouns.

Word	Noun	Adjective	Verb	Adverb
quadraphony	Yes	No	No	No
stereo system	Yes	No	No	No

As nouns, stereo system is a hypernym of quadraphony; that is, stereo system is a word with a broader meaning than quadraphony:

quadraphony: a stereophonic sound recording or reproducing system using four separate channels
stereo system: reproducer in which two microphones feed two or more loudspeakers to give a three-dimensional effect to the sound

Other hypernyms of quadraphony include stereo, stereophonic system, stereophony.

quadraphony (noun)	stereo system (noun)
a stereophonic sound recording or reproducing system using four separate channels	reproducer in which two microphones feed two or more loudspeakers to give a three-dimensional effect to the sound