My HSU sub has 2 identical ports. The sub runs in max extension with 1 port plugged and with both ports open, they call it max output. A switch is on the plate amp and is so labeled. I've always run in max extension mode since I never play at ear breaking levels. I'm training myself to recognize about 80db, which I find the sweet spot between low loudness and TOO loud. In max extension mode, it'll go to 16hz but not TOO loud. Just loud enough to rattle everthing in the house which isn't bolted down. Man, that sound carries.
Should I expect tighter or looser bass? It's still gonn go loud enough, my vol control on the sub is at about 3 of 10.
I did the obvious thing and just TRIED it. Seems to be somewhat tighter and more musical. I'll know more tomorrow when I can turn it up to about 80db and put on some music with a reasonable bass line. Just for example, on the XM jazz feed, string bass sounded more like.....string bass. more tomorrow after a little more listening...and adjusting.
As it turns out, the bass seems more tuneful and musical. I'll leave it the new way for a while and optimize without measuring anything. I've alread turned the crossover UP to about 35hz which is near the lower advertised limit of the panel. No 'bloom', either.
And, a question like 'should i expect tighter or looser bass?' is always an implied comparison with the change proposed.
In this case, the change is distinctive and for the better.
Low extension is / was not the point in making the change. I was hoping for more .... musical....bass, which I believe I got. String bass now has a nice twang to it when it was a little muddy before uncorking the 2nd port. Kick drums have better tone now and still have the gut feeling.
The dino footsteps in Jurassic Park still rattle the walls.
Haven't and probably won't try the Saint Sans organ piece with the new setup.
I run my panels full-range and don't want to subject them to a 16hz signal at any amplitude. That is easily 1/2 of the lower limit.... I did it once to just listen. That was enough! I did approach from the quiet side and never turned it up enough to get mylar slap.
If I had the ability to cut out LF to the panels, I'd than be tempted.