I have been revisiting some of my old projects - trying to improve a few where I just didn't do them justice the first time around. I've just started gluing up properly sized boxes for the TCP115-4. A 1 3/8" port should fit in the box with an elbow. But the velocity is going to be too high according to WinISD. Of course larger diameter ports would be longer than the height of the boxes. But I do have a pair of ND140-PRs that I tried with the previous TCP115 boxes I built. Those boxes were the wrong tuning for that woofer, but I noted the passives bottomed out really early. The displacement of the ND140-PR is over 3 times that of the TCP115, but their FS (44Hz) is lower than my desired box tuning of around 55Hz. Is this just a combination that won't work together or does the box volume somehow change the PR FS?