Two-speaker sound system (6)
I believe the answer is:
stereo
'two-speaker sound system' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for stereo that I've seen before include "System that gives a three-dimensional sound" , "Sound transmission through two or more speakers" , "Audio system, hi-fi" , "System of sound reproduction" , "Sound transmission from two sources through two channels" .)