I would also like to suggest you take a look at Acoustic Fields videos on you tube. Lot's of great information there available for free. Just my two cents.
difussor's
I "think" im in need of some sort of diffusing on front wall of small listening room...I would be really interested to hear some experiences of some that have been through it...don't think I need an absorber type...as I have some bass traps in lower corner...just lacking clarity of sound stage...diffusor?