Speaker is an online communicator (7)
I believe the answer is:
tweeter
I believe this clue is a double definition.
'speaker' is the first definition.
(tweeter is a kind of speaker)
'an online communicator' is the second definition.
'is' is the link.
(Other definitions for tweeter that I've seen before include "with high frequency?" , "piece of hi-fi" , "High-frequency speaker" , "Message sender" , "little Speaker" .)