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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 3 responses by folkfreak

folkfreak's avatar
folkfreak
1,349 posts
 
@ether the point @geoffkait is making is that any amount of acoustic foam is audible and deleterious.

I have a fully treated room with tube traps and diffusion along with a range of SR treatments. I was using small (6”x12”) bits of foam to break up reflections from the edges of my components. As soon as I took these out I realized they create a harsh and edgy timbre.  

Please don’t use any foam in your room. Treatments from GIK are quite cheap (I ended up with a pair of custom GOBOs to address my component stack issues) and will sound so much better. Even natural rugs or wall hangings will be better than synthetic foam
folkfreak's avatar
folkfreak
1,349 posts
 
@gdhal you will not hear any problems with foam and a clap test. However try playing female vocal, listen with and without the foam and listen to tonality rather than frequency response (ie try to tune out the Echo you are using the foam to address ). Better still try putting some natural materials (eg a rug or thick sweater) at the reflection points and compare the sound 

I am also surprised by your GIK quote, as their 2’x4’ spot panels are $60 each you must be covering a very large area - over treating a room is also a danger ...
folkfreak's avatar
folkfreak
1,349 posts
 
I’m sorry I was not able to communicate clearly enough. I’m not denying that acoustic foam will perform sonically and damp midrange tones. The issue is that in doing this it also imparts an audible sonic signature that is harsh and ultimately undesirable. I’ve had the same experience with synthetic rugs on the floor in comparison to wool, they work as advertised but you can hear the effect, it’s a sort of tinnitus like effect (ie a harsh but low level high frequency ringing)
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