I think on their own fixed directly to the wall, the foam would not be as effective at controlling the bass frequencies compared to if you could possibly mount the panels with a few inches of space between the panels and the wall. For the real sub frequencies, I think dedicated bass traps would probably work better. Quoting from this SOS article, (http://www.soundonsound.com/sos/feb06/articles/studiosos.htm
'In very general terms, a piece of four-inch-thick foam stuck directly onto the wall is only really effective for frequencies above about 200-300Hz, whereas a piece of two-inch foam is only effective above about 400-600Hz...One very useful tip is that spacing foam or Rockwool absorbers away from your wall by a few inches makes them more effective at low frequencies. For example, spacing four-inch-thick foam four inches from the wall is almost as effective as using double the thickness of foam in the first place'
If you are up for a bit of DIY (
), you can put your own bass traps together, saving yourself a few quid! I haven't used this guide, but on the gearslutz forum there's a sticky describing the process (http://www.gearslutz.com/board/bass-traps-acoustic-panels-foam-etc/87464-how-i-built-my-bass-traps.html
You can find some good tips on the GIK Acoustics website too, http://www.gikacoustics.com/index.html
, in the Education section, re speaker placement etc!
Also, you can complete the form on the Room Setup page to get some advice from Glenn Kuras (who also posts on gearslutz)! And I'm not sure if you know about the PSW forum, but I'll link it anyway in case (http://recforums.prosoundweb.com/index.php/f/44/0/
), they have another acoustics forum!
I hope you can find something of use here, sorry if I rambled on a bit!
Best of luck with the room treatment!