Yea placing farther apart is optimal,,, but I'm running those dual 18 with a qsc 2450 each, power is king! So it doesn't matter that much as to how far apart they are,,,, but yes about 27 ft apart if able,,,, will definately shake your bowels! Also I can optimize with my PA2 drive rack,,, it is amazing at tuning bass!
Thanks guys,,,,the sound is good,,, but my back is not so good! It cost me 50 x 2 bucks every show to hire young men to do the show with this rig. If not I have to ask for help.