Agreed, however with one single sub played louder, you might get an increase at certain spots in the room (more LF), but you will get deeper nulls in others.
More subs are meant not to increase the impact or perceived "volume," but to reduce the nulls (and also tame some of the peaks) across a wider listening space. That would, in effect, make some things seem quieter or that there is less LF output.
So I guess it comes down to super bass in a couple of sweet spots, or more normalized bass over a larger listening area.
Either can be considered "right" depending on the end goal.
Oh, my "rest of range" was in regards to the increase above 40Hz but still in the subwoofer's domain of sound reproduction (under 90Hz). I didn't mean the rest of all audible hearing. Check out the video I linked before and go to about 5:37 into it. It has the graph and Ian talks about how much less the gain is between 19Hz and 35/40Hz vs. the larger gain above 40Hz and under 90Hz. So if we only care about 1 sweet spot for a peak, and only want 19-40Hz reproduced well (based off of the Axiom tests in the video, individual rooms would differ), then we are all set with just 1 sub and to most that is perfect. Heck, I have had a 1 subwoofer setup for 18 years and loved it. I am only a month or so into my 2 subwoofer setup and I am finding that I am enjoying it even more. Not because I feel more of the really deep bass, but because my room's sweet spot was NOT where I liked to sit when watching a movie (my back row had better sound, but my front row is perfect for me for the immersive visuals). I've effectively expanded the sweet spot to include my seat and improved the overall under 100 Hz freq. response at the same time by improving the "above 40Hz" top half of what the subwoofer is producing for me.
Part of my limitation is that I couldn't do a subwoofer crawl, well not really anyway... I had to put my sub up front behind my false wall. That was the plan, and I could only move the sub right and left along that wall. Dead center would have put it behind the VP180 and between the two I would have lost about 6 feet of the room length to get them in the proper location with the proper spacing. I didn't want to give up more than 2.5' of depth, so that meant putting the sub between the center channel and one of the front mains (right or left).
So I am dealing with a less than ideal audio setup based on asthetics. Then again, we all are working with less than ideal spaces. To make a perfect room for audio would be pretty ugly, in my opinion, to accomplish for a home theater.
