Frequency Ranges & Effects?

I was wondering what frequecy ranges are not dependent on direction? I know a subwoofer can be placed anywhere in the room as it is not directional. But until what frequency does it go up to in order to have to be faced towards a person to hear? I want to make some mid-ranges to handle somewhere between 200-400Hz and not have to place it somewhere to see. If possible I want to place it along with my sub, no where to be seen.
 
Directionality will not be your only problem.

For accurate reproduction, all drivers must be the same distance to the listener. With a sub crossing at 100Hz it could be forward or rearward of the main speakers by about a foot, give or take, and depending. At 400Hz you only have a leeway of a few inches, again, depending.

All this assumes that the proper crossovers have been designed in the first place.

The more you depart from the correct way of doing things, for the sake of the wife/aesthetics/whatever, the less quality you get.

What's the point of such a narrow bandwidth for the mid-ranges you speak of?