Augerpro tested some port resonators, didn't work too well if I remember. However holes to relieve pressure nodes of port pipe harmonics work somewhat. Augerpro commented that some kind of chamber around the port to relieve to worked better (distortionwise) than just venting back to the main enclosure, with some damping material of course. That solution might also have some resonator thing going on.
For closed bass/mid enclosure this might work though, quarterwave resonators on the long ends damping modes that fall into pass band. Similar design like for the tweeter but perhaps only few chambers needed for those few lowest and problematic modes who fall on the pass band. One would have to care about impedance match, perhaps bigger box results etc. Perhaps just too complicated solution for most situations. Nice for tweeters apparently, but not sure if long wavelengths need this solution as there is possibility to crossover to smaller driver and box before issues, except with the tweeter.
I suppose so, resonant traps placed at 1/2 and 1/4 wavelength. I did try a chamber depth equal to 1/4 wavelength as he mentions, and is common in these sorts of traps, but it wasn't all that different in performance. Although my traps were pretty close to 1/4 wavelength already. I'm doing final checks right now, and that will include printing a larger port and see how things scale, chamber depth being one thing I need to focus on.