Sweet, of sound (6)
I believe the answer is:
dulcet
'sweet of sound' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for dulcet that I've seen before include "Sweet, gentle (tones)" , "Of voice or tone, sweet-sounding" , "Mellifluous, pleasant to the ear" , "Sweet on the ear" , "Sweet - melodious" .)