[andrebrito]

Can you tell me what are the dimension of that place ?

It seems this no longer belongs to small room acoustic but indeed to large room acoustics,so forget about bass traps in such a space. Indeed in bars and discos it is advantageous to place the PA system in the corners, like you have placed, to get that extra bass from the speakers, on the contrary of a recording studio.

You need to treat that ceiling, period. If you are worried regarding the aesthetics reasons of room acoustics treatment, you can use a perforated panel in it. This of course will be costly.

If you really want to use rockwool panels, for $$$ reasons, then don't fill that place with tons of panels. Air absorption already acts at high frequencies, due to the volume of the room and covering it with rockwool will end up with an unbalanced room. That is the main reason perforated or slotted panels are used in public large places and not typical rockwool panels we see in recording studios, they are tuned for mid frequencies absorption.

Adding some diffusers to the space can also help to correct some echoes problems, particularly at the stage, where musical intimacy is desired and also reflect some sound to the audience. You can also add absorption and diffusion to the walls but the ceiling is the first surface to solve, acoustically speaking.