Concert's opening with proficient conductor (5)
I believe the answer is:
'conductor' is the definition.
(I know that cable is a type of conductor)
'concert's opening with proficient' is the wordplay.
'opening' suggests taking the first letters.
'with' is a charade indicator (letters next to each other).
'proficient' becomes 'able' (able can mean capable or proficient).
The initial letter of 'concerts' is 'c'.
(Other definitions for cable that I've seen before include "Anchor chain; type of TV" , "Thick wire; telegram" , "Satellite alternative?" , "Strong line" , "Strong thick rope made of twisted hemp or steel wire" .)