A set of bars from composer (4)
I believe the answer is:
cage
I believe this clue is a double definition.
'a set of bars' is the first definition.
(a cage has bars)
'composer' is the second definition.
(I've seen this before)
'from' is the link.
(Other definitions for cage that I've seen before include "Imprison, confine" , "Eg, aviary" , "Wired enclosure" , "Barred container" , "In places squirrel's nest" .)