It seems the high pass filter should be enough. I have read that plugging ports can mess with the speaker performance intended by the designer. Could plugging the ports affect frequencies above the intended level at which the mains cross over to the subs? I guess the only way to know is to try it. In my system, I believe adding a HPF (Marchand XM446XLR) improved SQ when playing the system at higher volumes, but I do not perceive any difference at low-mid playback volumes. My current speakers are not ported so I cannot comment on the effect of both a HPF and plugging the ports.
Protip: Using a sub? Plug your mains
Merry holidays, or drinking season, whichever you celebrate I support you.
For those of you with ported main speakers and subs, here’s a big tip: Plug your main speakers.
It will reduce the bass output, but also greatly reduce the movement of the driver below the port frequency. This combination increases the dynamic range, and reduces distortion, especially when used with a line level high pass filter. It also often makes integrating the subs easier thanks to less overlap. Use a sock, preferably yours and clean unless you are some weirdo. You don’t have to stuff the entire port length, just plug the end tight. I won’t be held responsible for those of you who lose their intimates inside their speakers.