Detlof is right. A square room is likely to give you terrible standing waves. You might try firing the speakers in a diagonal fashion. Room treatment (bass traps will help), but a 4 meter room is going to give a bass boost around 43 Hz. Most room treatment doesn't work very well below 80 Hz. The only other alternative is to go to an active equalizer. Audiogoner's will accuse me of Heresy--but unless you can change the room's dimensions you need a notch filter around 43 Hz. If you can afford something like a TACT I hear they are excellent. If you can't, I would suggest a McIntosh EQ. Unfortunately, it is analog and in the signal path and will add noise--a small amount. The McIntosh EQ's are very good--but not perfect.
