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.
That is a cool trick. How did you measure the response? I may have to try this out sometime.
I used Room Equalizer Wizard … REW … https://www.roomeqwizard.com/ … it’s free and quite easy to use. You can get usable comparisons from it even without a calibrated microphone. It’s nice because it counts on you measuring from the sweet spot in a live room… so that response plot is not the speaker it is “those speakers in my room”.
You should note that the roll off above 8k is my microphone, not the speaker.