I just read on JL's site about port correction factor so let me see if I'm getting it right. Basically if you use a wall of the enclosure as a side of the port(slot design) then you effectively gain a bit of length to the port? Apparently because one side of the port doesn't end at the same place as the other, the speaker see's this as extra port length, half of the port height to be specific.
So in essence this can be a bad thing for those tuning higher and don't take it into consideration as it will extend the port and cause the tune to go a bit lower than expected. For those like me however who want to tune low you can use it to your advantage by getting a free inch or so on the port without actually taking up displacement?
Personally I want to tune my box low, but going as low as I'd like will take up gobs of space that I don't have. So when WinISD tells me to make a port length of 25.25" to accomplish a 29hz tune, then my 2" high slotted port design will add an extra 1" of effective port area giving me 26.25" and tuning a little bit lower? Assuming of course that I ingored the correction factor and built the actual port to 25.25".
Just making sure I have the basic logic down to decide whether or not to actually build the port without the correction factor or not. If it will cause more harm then I will subtract that inch off of the design. Seems to me like a free way to get a longer port without taking any displacement away. May be miniscule in the larger scheme of things but hey it's free.