FWIW, my room is 11*15, speakers along long wall, my seat < 1' from rear wall, which is treated w/ 4" thick bass panels behind my head, reflective side out; the ear ignores reflections < 10ms which a panel close to the head provides in mid-upper freq's while absorbing bass freq's which take longer to reflect and thus cause smearing, as Daverz mentioned.
i'm +/- 5db to 40hz or so IIRC. without room treatments, expect to be +/- 20db. seriously