corner traps with steel framing

hi! is correct to do the corner traps with steel framing?? or is better using timber framing?? I use in steel framin and sheetrock on walls. 8 cm of rock wool on corners is enough??

8 cm is OK, twice that would be noticeably better. It's OK to use steel framing, as long as you don't leave anything loose to cause rattles and you DO make sure the insulation fits snugly into the frames (rattles again) - If you were going to make these into slat resonators, I'd stick with wood framing... Steve