Recommended Air Gap For Back Wall Panels?

Thanks Hexspa.
Yes, I will measure and analyze but wanted to get the Best starting Spot. My room Sucks in the Low End.

So, you're saying, for better performance, that a 6" Air Gap is better than 4" which is better than no gap?

No need for more than 6"?

mrfye17 Here's something that explains the gap from Ethan's pages as you may have missed it: ethanwiner.com/acoustics.html

For a given thickness of absorbent material, the ideal air gap is equal to that thickness because it avoids a hole in the range of frequencies absorbed. For example, if you install fiberglass that is four inches thick with a four-inch gap, higher frequencies whose 1/4 wavelength falls within the four-inch material thickness are absorbed regardless of the gap. And for those frequencies whose 1/4 wavelength is between four and eight inches, the fiberglass is also at the proper distance from the wall or ceiling. This is shown below in Figure 6. Top

Response with an air gap
Figure 6: The higher frequencies (top) are absorbed well because their velocity peaks fall within the material thickness. The lower frequency at the bottom does not achieve as much velocity so it's absorbed less.
In practice, you don't necessarily have to measure wavelengths and calculate air gaps, and the first few inches of space yield the most benefit. Most people are not willing to give up two or more feet all around the room anyway, so just make the gap as large as you can justify. If you can afford to fill the gap entirely with material, all the better. And even though the velocity is indeed highest at 1/4 wavelength, there's still plenty at 1/8th of the wavelength too. Note that the angle at which sound waves strike a fiberglass panel can make the panel and its air gap appear thicker than they really are. Further, low frequency waves that strike an absorbing panel at an angle may be absorbed less than when they strike it at 90 degrees, due to a "grazing" effect. The explanations in this section are a simplification and are correct only for a 90 degree angle of incidence, which is not always the case.

Hmm, I'm sure I read somewhere Ethan saying you should not angle acoustic panels to divert reflections. Maybe he can chime in? I could be wrong, but I'm pretty sure I'm not.