Loudhailer (9)
I believe the answer is:
megaphone
'loudhailer' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for megaphone that I've seen before include "Loudhailer" , "One projects sound" , "Funnel-shaped voice amplifier" , "Cone-shaped device to intensify the human voice" , "Voice-amplifying device" .)