Old man holding sound-enhancing device — a character! (7)
I believe the answer is:
omicron
'a character' is the definition.
(I know this)
'old man holding sound-enhancing device' is the wordplay.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'man' becomes 'ron' (short for Ronald).
'holding' is an insertion indicator.
'sound-enhancing device' becomes 'mic' (microphone).
'o'+'ron'='oron'
'oron' going around 'mic' is 'OMICRON'.
(Other definitions for omicron that I've seen before include "Olympic character" , "character in Europe" , "A rounded character" , "character from Athens" , "character in Sophocles" .)