should I cover the back of my bass trap ? (absorbers)

Hi everybody I know it has already been discussed here, but I couldn't find a clear answer, and I'm confused My case : I have 3 clouds : Panels with 50 kg/m^3 compressed (28 kg/m^3 orginally) rockwool, 6 cm of depth, and 10 cm away from the ceiling. They are over my drumkit. Question : Should I cover the back (ceiling side) with a thin wood board ? (something like 0,5 cm) > thanks to this board it is easier to build the panel, because I compress the rockwool. Now I want to build the same panels but for the walls. I read here 5 cm was a good distance. Right ? And, should I also cover the back (wall side) ? I think the answer of my questionS is no, but I read that the reasons were different for wall panels, and ceilling panels Thanks everybody ! PS : Please, I'm French, don't use too complicated expressions :D

4-6cm should suffice.

very, very recent topics have addressed just those questions.... read the forum and update your knowledge :)

Thank you Gulfo ! I know it has already been discussed, especially in the first topic of this page. But it was talking about covering the BOTH sides, which isn't att all my question! I also read something like that : In some case you have to cover one side of a cloud why ?

Sorry but it HAS been discussed. But I'll give you the straight answer: Covering the back of an absorber might come in handy if you want that same absorber to reflect/bend sound. In case of a ceiling absorber (aka cloud) above a mix-station, for example, you want to break the first reflections by angeling the cloud and put a hard surface on the back (more mass is lower frq reflection). That's the reason why you wanna hard-back an absorber. Now, that info should be enough to cover all questions; you now know when or when not to. So, for regular wall absorbers which only intent is to absorb broadband frq you should NOT add mass to the back. Space it the same distance as your wool thickness if you can. good luck, don't forget to post pix when you build! ro