I’ve read a lot of outstanding reviews on commercial dual passive radiator subs lately, and would like to try to achieve the claimed benefits in a DIY project. I am waiting for delivery of two AV15’s any day now, and will be building two custom cabinets that will house my Ohm F drivers with their sealed compartments on top, and a down firing AV15, 500 watt plate amp, and two opposing 15″ passives in the base of each one. I haven’t yet found any definitive “how to” information on the subject of dual passives, and hope someone on this forum can direct me to a book, software, or a site that will give details and formulas to select the right diafragm weight to achieve the flattest 20 Hz or lower response I can get in a 4 cubes or less cabinet. I emailed John about this twice after the sale, but I guess he’s a busy boy right now. So, any help greatly appreciated!