Speaker less loud — whisperer of sweet nothings? (5)
I believe the answer is:
wooer
'whisperer of sweet nothings?' is the definition.
(sweet nothings might be whispered to woo someone)
'speaker less loud' is the wordplay.
'speaker' becomes 'woofer' (woofer is a type of speaker).
'less' is a deletion indicator (less can mean minus).
'loud' becomes 'f' (short for forte - 'loud' in music).
'woofer' with 'f' removed is 'WOOER'.
(Other definitions for wooer that I've seen before include "One courting" , "One who goes to court" , "Suitor" , "Man courting a woman" , "person to court" .)