The problem with 'adding' sub(s) is the crossover. If the monitors go down to say 50hz, and sub(s) range is up to 100hz, or whatever, you are doubling up a 50hz range, leaving a seam in the intetration. Plus the mids of the monitors are still getting low frequency info and continue to strain under it.
With an active XO the mids can cut off at the same frequency subs are engaged for improved integration. Best is probably 100-120hz depending though.
Indicating there is something to be said for aquiring a system that is already designed. Then all that is needed is proper setup for you room.
Anyway, check out the study paper on woofer location: http://www.linkwitzlab.com LINKS link/ 'Subwoofers: Optimum number and location' / 'Getting the Bass Right' link
Both my dble 12" subs http://www.linkwitzlab.com / Phoenix / Woofer, are on the side wall next to the main panels http://www.audioartistry.com / Dvorak, severl feet from the wall behind (and those problematic corners) for that very purpose.
With an active XO the mids can cut off at the same frequency subs are engaged for improved integration. Best is probably 100-120hz depending though.
Indicating there is something to be said for aquiring a system that is already designed. Then all that is needed is proper setup for you room.
Anyway, check out the study paper on woofer location: http://www.linkwitzlab.com LINKS link/ 'Subwoofers: Optimum number and location' / 'Getting the Bass Right' link
Both my dble 12" subs http://www.linkwitzlab.com / Phoenix / Woofer, are on the side wall next to the main panels http://www.audioartistry.com / Dvorak, severl feet from the wall behind (and those problematic corners) for that very purpose.