Supporting scheme, man becomes loud and mournful (8)
I believe the answer is:
plangent
'loud and mournful' is the definition.
'supporting scheme man' is the wordplay.
'supporting' says to put letters next to each other (in a down clue, some letters go under others).
'scheme' becomes 'plan' (I've seen this before).
'man' becomes 'gent' (gent is a kind of man).
'plan'+'gent' is 'PLANGENT'.
'becomes' is the link.
(Other definitions for plangent that I've seen before include "Clangorous" , "Resounding" , "booming" , "Of sounds, resonant and reverberating" , "Resonant, reverberating with mournful sound" .)