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Music LED Light Box
A 6" panel def would not need an air gap. But most DIYers use A shallow depth frame to match the roxul, and mount them flat on a wall. I totally agree an air gap on a 6 is thick enough that you don't need it and it will def outperform 3.5-4" Panel.
Nice Acoustic Panel a Design!I like how you placed the acoustic insulation panels flush with the face of the frame, creating the airgap required all from within frame itself. As most absorbers that are DIY most do not account for the air gap making them almost non absorbent. Nice Job!!.
The Acoustic Insulation in the front on the face isn't a common practice for wall mount absorbers, But..... Is extremely effective as it creates the required airgap to make the acoustic panel as a whole very effective. No Airgap=Minimal absorption, 1" or Greater Airgap for a wall mount 2x4 Panel will be Very effective
Simple Elegant Guitar Stand
Galvanized pipe and glass insulator wall sconce