Woofer's counterpart (7)
I believe the answer is:
tweeter
'woofer's counterpart' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for tweeter that I've seen before include "One may follow another" , "highly effective in reproducing sound" , "one delivering a short message?" , "Social networker" , "Robin, for one" .)