Sound system bent trees round (6)
I believe the answer is:
stereo
'sound system' is the definition.
(stereo is a kind of sound system)
'bent trees round' is the wordplay.
'bent' is an anagram indicator.
'round' becomes 'o' (round can mean a round object).
'trees' is an anagram of 'stere'.
'stere'+'o'='STEREO'
(Other definitions for stereo that I've seen before include "Twin-channel sound" , "Of sound equipment, having two speakers" , "Means of amplification of sound through two or more channels" , "In-depth" , "Music player with two speakers" .)