Principal decided to provide piece of audio equipment (7)
I believe the answer is:
headset
'piece of audio equipment' is the definition.
(headset is a type of audio equipment)
'principal decided' is the wordplay.
'principal' becomes 'head' (synonyms).
'decided' becomes 'set' (I've seen this in another clue).
'head'+'set'='HEADSET'
'to provide' is the link.
(Other definitions for headset that I've seen before include "listening equipment" , "Earphones and microphone assembly" , "equipment for telephonist" , "Communication kit" , "Audio communication equipment worn by pilots, DJs etc" .)