Sound of setter filling puzzle up for speaker (9)

'speaker' is the definition.
(type of speaker)

'sound of setter filling puzzle up' is the wordplay.
'sound of setter' becomes 'woof' (setter is a type of dog).
'filling' means one lot of letters goes inside another.
'puzzle' becomes 'rebus' (I've seen this before).
'up' is a reversal indicator (in down clue: letters go upwards).
'rebus' reversed gives 'suber'.
'woof' placed inside 'suber' is 'SUBWOOFER'.

'for' acts as a link.