Small room....treating 1st reflection points

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.

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

http://www.amazon.com/s/ref=nb_sb_noss?url=search-alias%3Dmi&field-keywords=corning+acoustic+panel&rh=n%3A11091801%2Ck%3Acorning+acoustic+panel