correct duct size??

[rudy sesztak]

I use 2 jbl d123's mounted side by side used from approx 50hz to 7khz without a crossover( that can cause problems) they roll off approx 12 db an octive above 7 khz. jbl 077's go above 7khz. the 2 d123's project like a big horn,but with no horn coloration. the equalized system sounds GREAT!! jbl had a c35 cabinet,that used 2 d123's in it. i found on line the duct size for 1 d123 in the c35,but not with 2 d123's in it. Thanks for any imformation on the correct duct size for 2 d123's in a aprrox 6 cubic ft cabinet thanks- RUDY