Permanently sealing a vented subwoofer??

I have used foam bungs to mitigate boomy bass where there was no option for repositioning or replacing speakers. It doesn't always have the desired effect, but it often improves boomy / slow bass, it costs next to nothing, and it's instantly undone if it doesn't work out.

I would imagine that the effects of the port tube will be minimal if it is bunged down a significant proportion of its length.

Nice theoretical desctription. It is pretty obvious that the acoustic suspension of a vented box is different to that of a sealed box, and that this will affect the mechanical action of the drivers.

The only problem with the theory is that foam plugs can actually work to give the desired effect. I grant you the solution is not optimum, but if buying new speakers, or changing their room placement is not an option then plugging reflex ports can get the job done adequately.