Explosive sound (3)
'explosive sound' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for bang that I've seen before include "precisely" , "Slam" , "Sudden impact" , "Straight fringe of hair" , "Report - something the hairdresser did?" .)
(Another definition for bam that I've seen is " hoax".)