How to "mount" acoustic foam ?


My main system is in my partially unfinished basement.
While I have finished the ceiling and have nice floors / rugs - I do like the industrial / rough look of the concrete walls....I just finished painting them but don't want to install any sheetrock / finishing material.
Instead I want to buy acoustic foam (2inch depth squares) and mount them to the walls - front / back and sides
And here are my questions:
1. Should I just use glue and apply the foam squares directly to the wall ?
 - IF YES - what glue should I use? I know there is the special construction glue for laying floors etc..... I now they sell it also for concrete and stone application - sold in caulk like tubes 
2. Should I first apply the foam  to a plywood / wood and anchor that to the floors ?
 - IF YES - I would imagine a few concerns: 
-  Will that wooden structure bring about sound resonance that I am actually trying to control ? (Wood isn't as bad as concrete but still....) 
-  Will I have to add a layer of caulk or similar filler between the wall and  the wooden panel? Obviously the concrete walls are not super smooth so the wood panels will not be in perfect and uniform contact. They will be held rigid with the specialty screws drilled into the walls....but still 
- What type of panels should I use....I was thinking anything from very thin cardboard like materials (to minimize any resonance from wood) to 1/2 inch plywood for rigidity.
IN SUMMARY: 

 I am leaning for the 1/8inch thick boards - In my mind it would provide smooth surface to mount the foam onto, retain the acoustic profile of the foam, and then just hold it all in place up on the wall with 4 bolts (each corner)

Anyhow....Any other tips and advice about proper installation would be appreciated.

Thank you!! 
ether

Showing 2 responses by noromance

Per @slaw and @geoffkait , I removed the 4 x 24x48x2" acoustic foams I installed a few weeks ago. When first installed, there appeared to be an improvement in control of the music with better depth. However, after some further listening tests, I have to agree. While the sound is a little "wilder", it is freer. The music breathes, is louder, more dynamic. The foam basically killed the music. I have found the same effect with some mats. Damping can be deleterious. 

I used the term deleterious. I am not denying that the foam tamed certain aspects of the sound. It did. And extremely effectively. Bass was reduced by a significant factor while higher frequencies were "tamed". Whether foam sounds bad in itself, I do not know. All I do know is that it took the life out of the music. I tried reducing the amount of foam gradually and each reduction improved the dynamics, bass and loudness. This has been an interesting excercise. I do believe the space needs some treatment as it can be a little "live."
However despite it being in a corner of the basement, there is a lot of free space for the sound to dissipate into so reflections etc. are not as bad as might be imagined from the photos. There is some "confusion" in the upper mids when played loudly and mid bass is a little plummy on some recordings. I will look into the options mentioned. Thanks.