I just modeled the Kappa Perfect 12.1 in WinISD with your box size of 4.05 cubic feet and the port you mentioned 16"x3"x54". It seems your tuning frequency will be 23Hz with first port resonance at 125Hz which will be okay if you integrate the subwoofer with a sufficiently steep crossover. \r\n\r\nIf you properly round all the corners and use a radius of at least 1" I highly doubt you will have any audible chuffing. I know I haven't. Be sure to have rounded areas placed at the junctions where the slot intersects with the cabinet if you round the port otherwise your effort will be in vein.\r\n\r\nI think your winISD has way more functions than mine, otherwise i would have been experimenting with these things ;) (winsid beta 0.44). With this tuning freq (23hz) will i still be able to output the lowest end 18hz at audible (well, not audible i suppose, but "feelable" :P) levels?