Reflections of sound waves (6)
I believe the answer is:
echoes
'reflections of sound waves' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for echoes that I've seen before include "Resounds, reverberates" , "repercussions" , "Repetitions of sounds" , "Sounds reverberating" , "parrots" .)