I find this video and all the control and recording room has the same slats wall but it seem it hasn't nothing behind the slats. What do you think about it?
I'm not sure there is nothing behind the slats. Hard to be certain. There might be insulation up against the wall. But even if there is nothing in there, that doesn't mean they wont work: it just means that the Q for each salt will be very high, and the absorption won't be maximum. There might be reasons for doing that.
The slats are 2, 4, 6, and 8" widths (randomly applied) with spacing approx 1" between (the spacing is the depth of the board), the boards are rough cut lumber applied at an angle. There is traditional acoustic insulation behind the slats, but the "magic" happens in the labyrinth of bass traps in the ceiling system. The wall treatment alone helps a lot though... warm reflections with some diffusion, and absorption by the insulation behind the slats. Hope this helps!
OK, so from what he says it looks like they aren't actually meant to be slot resonators at all: more for decoration, reflection, and a bit of diffusion. 1" by 1" slots over really deep air gaps like that would be tuned very low.