The PRs moving mass dampening is adjusted to be equivalent to the air compression dampening of a vent. I've read a lot that group delay is indicative of SQ, namely transient response, which doesn't vary according to vent vs PR
Also, something about the AE PRs makes them more capable of lower frequency SPL than the VMPs, and they each consume just 0.05 cubic feet. However, PRs are still limited by excursion, whereas ports are not. Even with 3 PRs, there is still a portion of the max SPL clipped off when compared to ported with the same volume and tuning. When I carefully optimize the tuning, enclosure size, and vent size to the smallest vent volume possible without too much air flow noise, the same PR
configuration is still 25% smaller overall. But then I found, at least with the LMS Ultra, that when tuned low enough, they become equal in overall size. Eight cubic feet tuned to 15 Hz consumes a net 10.6 cubic feet when adding vent volume. Equivalent response with PRs requires 3 PRs with the same net 10.6 volume, and would still have some of the response clipped due to PR
excursion. So I'm probably just going to go ported with 8 cubic feet tuned to 15 Hz. Keep in mind, I'm carefully minimizing the port volume by keeping the air flow around 20 m/s at 116db@20Hz, and around 35 m/s at 120db@20Hz, assuming the higher air speed would still remain inaudible when the sub is hitting louder.