I input all the #'s for box size, fill, resonant frequency, etc. . . then I hit the optimize option to find out what port size & lenght I need to get a tune of 19hz out of my 750liter box with 2 front firing tempest drivers. It tells me that I need a port that is 2.9 centimeters long & 8.9 cm in diameter? Surely this can't be right. . . . What am I doing wrong?