Foam Plugs

If the plugs are closed cell foam; the alignment becomes an acoustic suspension. If the foam is somewhat open; it will serve to partially damp the port's output.If your speaker's placement was say, closer to the corners of the room; they could serve to reduce any boominess that resulted.

Mr T- Yes, I do understand your point. However, most make no distinctions between sealed box and 2nd order/acoustic suspension designs nowdays. ie: This site moves directly from a 2nd order alignment(calling it variously, "2nd Order", "Acoustic Suspension" and "Sealed Enclosure"), to a 4th order alignment: (http://www.danmarx.org/audioinnovation/theories.html) I do agree that IF the woofer and enclosure were optimized as a 4th order alignment, it would not be optimized as a 2nd order, with the vent sealed. BUT- the woofer would still be operating with the enclosure volume acting as an air spring(acoustic suspension). Actually- Villchur came up with the "Acoustic Suspension" design around 1954, and started building speakers with Henry Kloss, somewhat before A. N. Thiele published anything concerning speaker parameters, or cabinet alignments(around 1961), so things could actually get (somewhat)"optimized."

Mr T- They laughed at Bob Fulton too, when he'd walk into a shoppe with his 'Gold's'. The laughing stopped, when the music started. Look at the revolution in cables he started. Mr E- There are a few drivers available, with fairly long throw voice coils and wide surrounds. If one were really intent on loosening the compliance more for a true Acoustic Suspension design; they could do what Villchur did, and cut away most of the spider(leaving just enough to keep the VC aligned in the gap).

It would be nice to know what size woofer you're talking about. The last drivers I shopped for were 10", and that's been a couple years ago. I couldn't buy the drivers that Lyngdorf used in their W210(raw) or anything equivalent, so I stopped shopping and stuck with my Nestorovics. Change the compliance(like by skeletonizing the spider) and/or moving mass, and you'll change the free air resonance(the Cms will change over time also). Lots of variables.