Permanently sealing a vented subwoofer??

Foam in the vent will not stop airflow, but merely change the velocity and volume of the air movement.

The original premise that sealed is superior to vented is suspect. If properly designed either type will work. It's a question of trading off different sonic and/or practical compromises.

Foam bungs? Great name for a band.

Well designed ported subs (most), and I am talking about true subs here...work as well as sealed IMO.

Ported bookshelf and mini speakers are a different story, most try to do a little to much, with very few well designed examples that I have listened to...thump, thump, thump...chug, chug, chug.

Small room and low volume is the best many can do before the port noise sets in.

Dave

lol great band name!

For any given driver (raw speaker), the box size for a good sealed box is usually biogger than the proper size ported box. When you put a driver in a sealed box that is too small, you get amplification at resonance - in other words a peak in the response. This will make the sub sound boomy. How much will depend on the very specifics of the driver and box. I would say go ahead with a temporary blockage. Maybe a block of wood held over the port with bungee cords around the sub. I agree that sealed boxes are almost always better than ported, so it's a worthwhile experiment. Also, make sure you get a good seal. Any leaks will become small ports with there own small wavelength resonances, which will sound like whistlilng. Kind of like the sound a pigeon makes when it flies if you are close to it.