It's actually pretty simple, the EQ will lower the amplitude, but it doesn't take care of ringing.
It's unfortunately not that simple at all.
In theory, at least down low,
time and frequency response are the same thing! If there's no peak, there's no ringing. Simple as that.
However, my experience (and I'm curious if others have shared it) is that a well-EQ'ed sub in the corner will still give "room boom." However, multiple subs with a similar measured response, will not.
(properly measured, i.e. a spatial average of the sound power over the primary listening position.)
To further muck things up, a single EQ'ed sub in the nearfield (say, close enough for you to be able to kick the cone in) can sound quite clean, so long as one stays in the nearfield.
Subs generally work best in multiples of 2. So, 2, 4, 6, 8, etc.
No.
There's nothing magic about even numbers. In fact, even numbers can get you in trouble, because there's a tendency to place even numbers subs symmetrically.
Symmetrical placement (due respect to Welti and Devantier, who didn't study asymmetrical placement in the oft-cited study) is not the right way to go. At least if one's goal is to
randomize excitation of room modes such that the overall field is smooth. (My experience with different multisub configurations over the past 7 years or so has convinced me that goal is the right one.) The best way to do that is to use subwoofers of varied tunings, randomly placed in the room in all three dimensions. (Height is the oft-overlooked one.)
Yes, more expensive, but, as you found, two gives the possibility to flatten room response dramatically.
I used three, not two, subs.
One subwoofer can get a single listener pretty good response,
With room-boom, IME, unless the sub is in the nearfield.
With 2 subwoofers, the amplitude around the room can be tweaked much easier by allowing the subwoofers to 'cancel and fill' using proper placement.
Still, doesn't solve the time domain.
Subjectively, as I wrote above, yes it does. (I haven't taken time domain measurements, because I don't see them as terribly useful. See Toole's discussion of time domain resolution in
Sound Reproduction.)
Keep in mind that a subwoofer can act as a source as well as a sink. That is to say, it can also remove energy from the room! Otherwise, peaks would never be reduced by the addition of extra subs.
Folks. There are plenty of threads out there where measurements were taken before and after room treatment. I can't recall any threads in the dedicated build forums where people who applied room treatments actually had a worse sounding room, and worse measurements.
Well, if they were worse they probably wouldn't have been posted.
But there aren't any objective metrics for the two things we're primarily talking about here, image focus and spaciousness. Yet, at least.
For movies, that might not be an issue. I don't care about movies, however. I'm concerned about the reproduction of music.