Speaking of acoustics:
I got accused of careless shooting once when I was shooting downward at a mud bank in a sparsely-populated Light industrial/Agricultural area.
I was shooting (.22LR auto pistol) at near perfect right angle into the muck. I could see the nice little round holes/craters punched into the mud near my targets of opportunity, leaves that had settled on the goo.
Not one of them got away, as far as I could tell.
But a person came up from the opposite direction from my shooting and claimed he had heard several ricochets "going right by my head." They always seem to go "right by my head" for some reason.
I apologized and quit shooting and did a little investigating after he left.
I then popped one more, again into the muck, but without my ears on, and sure enough, I heard a pwang! from behind me.
This is a little hard to explain, but there was an industrial building about 150 yards behind me which was built out of those concrete T-sections set upright so that the flat side faced to the inside of the building, with the web of the Ts facing to the outside, and at a slight angle to where I was shooting (perfectly legally by the way.)
So there were about 20-30 vertical strips of concrete on the building about five feet apart which were successively echoing the sounds of my shots to make the "pwang" noise!
He wasn't hearing ricochets, he was hearing successive echoes from the vertical strips on the building.
Darndest thing.
I went back to shooting with no worries that my bullets were going anywhere but into the squooshily safe mud bank.