You may be in luck if it's a padded cell. Otherwise you're going to have a lot of reflections. You need something rolled off on top I think. Most mini-monitors that are designed for near-field listening also have very good dispersion and will sound bright if the side walls and ceiling are too close. I use very inexpensive speakers in my home office that have a nicely rolled off top end.
Here's an unusual suggestion. If you search through the recent Audiogon/AudioWeb/Audioreview/AudioShopper speaker ads you will find a pair of vintage KLH Model 5's for sale at $225 by someone in Maryland I think. They are very heavy 3 way "bookshelf" speakers requiring stands. Put them up high and toe them in and they are very linear, have really deep bass and sound great at low volumes. (You cant play very loud in such a small room, and these speakers are about 77db efficient.)
Here's an unusual suggestion. If you search through the recent Audiogon/AudioWeb/Audioreview/AudioShopper speaker ads you will find a pair of vintage KLH Model 5's for sale at $225 by someone in Maryland I think. They are very heavy 3 way "bookshelf" speakers requiring stands. Put them up high and toe them in and they are very linear, have really deep bass and sound great at low volumes. (You cant play very loud in such a small room, and these speakers are about 77db efficient.)