So this job is practically done. Thanks again for all the advice, especially Stuart
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I have a quick question about that & leaves. I'm making broadband absorber panels (with Rockwool etc) and not sure if I should leave a small air gap inside the back of them and the wall? Would this create a triple leaf effect? i.e. damaging the soundproofing aspects?
No. It won't do any harm to your isolation, since it absorbers are not massive, not sealed, not rigid, etc. Not a problem.
Leaving a gap between the insulation and the wall can extend the absorption down lower, so that's a good thing. As long as the absorption itself is fairly thick, then leaving a gap is beneficial. Sometimes you hear people say that the gap MUST be the same size as the thickness of the insulation (eg 2" insulation and 2" gap, 4" insulation and 4" gap), but that simply isn't true. You can ignore that advice, and make the gap whatever size it needs to be to cover the frequency range that needs to be covered at that spot in the room.
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