One problem of small rooms - especially small, square rooms - is the resulting large peaks and dips in the bass region due to speaker/room interaction.
If you can place the speakers with some assymmetry in the horizontal plane, relative to the room walls, that would probably be somewhat beneficial in the bass region. For example, instead of having your speaker-listener-speaker triangle nice and symmetrical within your 12-by-12 square, try rotating it either clockwise or counter-clockwise (as seen from above) by about 20 degrees. This will make the distances of each woofer to its nearby room boundaries different in both the lengthwise and widthwise dimensions. The purpose of this is to stagger each woofer's room-interaction peak-and-dip patterns in the bass region as much as is practical, as the resulting average (which is what your ears hear in the bass region) will be smoother.
The other problem presented by a small room is the relatively early onset of reflections. In general, reflections arriving earlier than 10 milliseconds after the first-arrival sound (corresponding to a path length difference of about 11 feet) are likely to be detrimental. Ten milliseconds isn't a hard cut-off threshold; it's more like the center of a fuzzy transition zone. Anyway, in my opinion fairly directional speakers may be your best bet in speaker type for this application, or at least speakers with a fairly smooth power response. Ideally, the speakers could be aimed such that the early sidewall reflection is off the opposite wall instead of the wall near the speaker (I can go into some detail about this if you'd like). Such directionality calls for large drivers, which means mini-monitors won't be ideal in this respect. In the interest of minimizing the audible effects of early reflections you might want to place diffusion or absorption in the early reflection zones, but in my opinion don't overdo the absorption or you'll end up with a lifeless-sounding room.
Duke
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