Small room....treating 1st reflection points

It depends on frequency range. I bought 2" thick double density fiberglass foam panels - Johns Manville 817 (not installed yet). Sound absorption table shows good absorption at 250Hz dropping to 0.38 at 125Hz. For the lower frequencies 4" might be necessary. Anything helps but rugs or curtains absorb only at higher frequencies. I suspect that if you can hear sound thru the rag holding it in front of you, then sound will be reflected from the surface behind it as well (floor wall etc). 4" panels placed some distance from the back wall would be great but it is expensive and impossible in my living room.

http://www.specjm.com/files/pdf/ci-9.pdf

Assuming that you place speakers on shorter wall, your room will amplify 1125/(2x14)=40Hz

@Kijanki,
My room multiplies out to amplify 36.75Hz. What table shows how to treat that frequency? Size, shape, density etc. Any recommendations would be appreciated.

This advice was given to me by Roy Johnson of Green Mountain Audio speakers. If the foam you have is high density foam, like what's used for seat pads of furniture, you'll get very good benefit at the highs and mids if you cut a 4' by 4' piece of peg board in half and make a pair of 2' by 4' panels about 2" apart on the one side by spray gluing your foam to the peg board, then wrap it with a very transparent (easy to see through) fabric. Spray the glue on the peg board, not the foam--that way it doesn't clog the pores of the foam. Hang them on the wall spacing four 1" thick spacers on each panel so the sound may travel behind the them. 2 on each side would require double the materials, but would be highly effective at the 1st reflection points. If your foam isn't high density, go online and buy 2" and get even more benefit--it will cost you about $100-125 for all 4 panels for everything needed.

I have a 10x11 room and I recently treated my side walls with Vicoustic Cinema Round panels. I am absolutely stunned the difference it made. Please check out my system thread for more details.

Tom6897, Look at the link I posted. Table shows sound absorption vs frequency. I was mostly interested in taming slap echo and mid-bass frequencies. These panels are glass rigid foam. I've read that organic foam has non-linear characteristic (of absorption vs. frequency, I assume).

36.75Hz is pretty good. As long as room doesn't amplify around 60-80Hz, where many speakers have "hump" it is OK and might even help to reinforce extension.