ok so my neighbour is a dancer... she works nights... she couldn't take to sub any longer! so I'm building a studio
at a mill space I'm renting I've read loads on acoustics and understand it for the most part.. just a few bits i could do with some help on
heres the layout of my room (the room is sort of a plasterboard room in a brick room)
my room is W 9.1 L 15.8 L 8.5 plasterboard ceiling and concrete floor

i was thinking of installing some absorbers on the front and back wall built into the studding would it be worth it if the rock wool is only
3inches thick? and would i still need traps over the corners?
also i was thinking of putting a stud wall absorber in my vocal area and under the stairs which both have a large voids
what would be the most effective way to fill the space behind the absorber because i have tons of high density rock wool insulation so i could fill the whole space if that would help with the lows with maybe an air gap?
absorbers are in grey

heres a general room pic (sorry for bad light)

im not sure what the room sounds like yet but i have the chance to build absorbers in but only this week and didn't know weather to go for it or wait and just do absorbers/traps in frames
thanks in advance for any tips i really appreciate it