Increasing the mouth size to 14" x 28" yields 392 square inches, very close to the proposed horn you mentioned. 5.5" x 5.5" inch throat is very close to the proposed 30". Am I correct that the radiation angle expanding to the desired mouth size will dictate the horn length? By length, are you refering to the axial length from throat to mouth? Sorry, a little hand holding required. Would the 2012 perform well with this lower cutoff frequency or would the 2206 be better suited. There is a large difference in efficiency between the two units. Thanks, Jerrod