Effective low frequency absorption can be achieved by spacing a porous absorbent out from the wall. A spaced porous absorber can be as effective as a non-spaced absorber of the same thickness. This is an inexpensive way to get improved performance – within limits. The image below shows the effect on the absorption coefficient of furring 1-in glass fiber wallboard out from a solid wall. Spacing 1-in material out by 3 inches makes its absorption approach that of a 2 in material (Everest 195).
Simply put, adding air space (of any amount) behind a panel, will increase its performance. This is why we add 1 inch of air space behind all of our products. If you desire more space, we have mounting options that will allow you to offset the panels from the wall even more.
References
Everest, F.Alton, and Ken C. Pohlmann. Master Handbook of Acoustics: 6th Revised Edition. 6th ed., Mcgraw-Hill Professional, 2015.