Refuse to reduce the volume (4,4)
I believe the answer is:
turn down
'volume' is the definition.
(I have seen 'Lower volume' mean 'turn down' so perhaps 'volume' could also mean 'turn down')
'refuse to reduce' is the wordplay.
'refuse' becomes 'turn' (I've seen this before).
'to reduce' becomes 'down' (I can't explain this - if you can you should give a lot more credence to this answer).
'turn'+'down'='TURN-DOWN'
'the' is the link.
Can you help me to learn more?
(Other definitions for turn down that I've seen before include "prepare bed" , "Spurn" , "Reject - reduce volume" , "mark the place" , "Refuse - to reduce the volume" .)