Room within a room - door threshold problem... concrete or??

Hey guys, I've got the traditional room within a room model going up in a small 13 X 9 isolation recording room. The trick is that the existing wall BEFORE the 4" air gap, needed to be "elevated" (stepped up) due to height restraints and differing doors (slider on existing wall) and beefed up solid core on "new" inner wall. My question is that now I have this elevated step up before I get into my 4" air gap between the two doors, If I use concrete (Will be around 6" high and 32' Wide) and leave a 1/2" gap between existing door threshold, and new door threshold, will this be ok? I can't think of another material that is robust enough to handle lots of feet etc.. I thought of using rigid mineral wool, but it will tear, break up, and generally start looking bad. Any other suggestions, I'm more than open to hear... Thanks!

Hi. Please read the forum rules for posting (click here). You seem to be missing a couple of things! :) Regarding your question: I'm not sure I fully understand what the issue is, so please provide photos and diagrams to make it more clear. if you are referring to the need to have something solid on the floor in the gap betwwwn the inner-leaf door threshold plate (where the seals are) and the outer-leaf door threshold plate (where those seals are), to raise up the level so that it is the same as the level of the threshold plates themselves, then I normally use wood for that. A strip of wood thick enough to provide the necessary increase in height, and almost wide enough to cover the complete gap between the plates, except for a gap of a few mm on either side, which I then fill with good-quality extra-flexible caulk, and cover it all (except for an even smaller gap, also caulked) with the same type of laminate flooring that I use for the actual studio floor. You say you need to raise the level 6", so a 2x6 planed down 1mm, laid flat, with 5mm underlay and 8mm laminate would work out perfectly. But I'm not sure if that's what you were asking... - Stuart -

Thanks Stuart for your feedback. Yes, the question is related to the door thresholds being about 6" in height difference from each other. The only reason I was thinking a concrete "block" was to minimize any transference as this spot is the only are area around the room that doesn't have a complete 4" air gap. But good to know that you would be confident enough with wood. Thanks again, and cheers! Christian