Instruments, loud instruments (6)
I believe the answer is:
flutes
'instruments' is the definition.
(flute is a kind of instrument)
'loud instruments' is the wordplay.
'loud' becomes 'f' (short for forte - 'loud' in music).
'instruments' becomes 'lutes' (lute is a kind of instrument).
'f'+'lutes'='FLUTES'
(Other definitions for flutes that I've seen before include "High-pitched woodwind instruments" , "Musical instruments as for James Galway" , "Wind instruments as played by James Galway" , "Pipe-like musical instruments" .)