Here’s a little trick I picked up maybe 10 years ago.
I was joking around with a friend who had asked me to look at his speakers and see if there was something I could do. We talked about several ideas and then he bluts out “Why don’t you just stuff a sock in it” and we did. It mostly solved his problem, too.
Since then I’ve refined it a bit and found that acoustically treating the inside of Bass Ports can often improve the low bass response. Take a look at this picture of my Cambridge Audio speaker… see anything odd?
Ok a close up on the port…
That is a foam rubber tube lining the inner wall of the bass port. When I got these speakers they had a pretty sharp low-end cutoff of about 43hz, with the tube in the port they get down to 31hz at -6db.
Hope this is helpful ….