They recommend 1000 hz at 6db/octave, but I've seen some systems made with them crossing over at as low as 800-900 hz if using a steeper slope.I've got most of the items used. So far I'm in at about $1500 for the drivers alone, still need another pair of 30" ribbons so that will add another $850 or so, crossover components would be extra on top of all of that as would cabinet construction.