Your experience of moving to two subs

The oomph is not the goal for me, either. The goal is evenness, tightness, naturalness. It's like having a room with two vents for heating/cooling rather than one. It is about distribution of waves, in either case.

Guessing about subs is an infinite project. I suggest a umik and REW and some time spent measuring.

If your subs have adjustable phase, like my Rythmiks, that will help a lot. Sometimes subs need to interact in certain ways to create evenness. Adjustable phase makes that much easier. 

Two 👍👍 for two subs!

@hilde45  Is 100% correct.

"The oomph is not the goal ...... The goal is evenness, tightness, naturalness."

My findings indicate that two subs are better than one and four subs are better than two. 

According to acoustics and psychoacoustics researcher Earl Geddes, the in-room bass smoothness increases in proportion to the number of independent bass sources. So two subs can theoretically be twice as smooth in-room as one sub; four subs can theoretically be twice as smooth as two, and so on. "Independent" in this context means that the subwoofer locations are acoustically completely and significantly dissimilar, and in practice that just about never actually happens; for instance even if both subwoofers are placed asymmetrically with respect to the walls, both of them are probably still on the floor, thus they are both the same distance from the floor and ceiling.

That being said, imo two subs intelligently distributed will make a very much worthwhile improvement in in-room smoothness versus only having one sub. Ime a steep-slope low-pass filter (like 4th order) can be very helpful for rapidly rolling off the top end of any subs which are positioned well away from the main speakers.

And "smoother" bass = "faster" bass, subjectively as well as literally, because it is the in-room bass peaks which take longer to decay into inaudibility and which therefore muddy the bass response.

Improvements in smoothness in the bass region pay disproportionately large dividends. This is because our ears have a heightened sensitivity to changes in SPL in the bass region, which is shown by the way equal-loudness curves bunch up south of 100 Hz. A 5 dB peak in the 40 Hz region can be comparable in perceived loudness to a 10 dB peak at 1 kHz!

The improvement in bass smoothness tends to extend throughout the room, which makes equalization more likely to be an improvement over a large listening area. With just one sub, equalization tends to fix problems in one location at the expense of making things worse elsewhere. So two (or more) subs intelligently distributed have the added benefit of making equalization beneficial across a larger area.

Duke (manufacturer of a four-subwoofer system)

Here is my take in this topic. Their is nothing wrong with one sub in a system if you implement it properly if you have the right resources. Yes dual, quad, etc, no matter how many subs you put in a room is going to improve the smoothness of the response but doing it without the use of tools and listening it not going to solve by itself especially in a room that is untreated. I have a small room where my system is and really might not require a sub but I have it for use of my listening preference, type of music, etc. My sub is set low 50s with the phase inverted. I dont have the sub in the center because I have the component rack in the area. So the sub is off center to the left about 1/4 wavelength of 1/2 of the room node, in this case around 60hz. This is almost 1/3 octave above the sub crossover frequency. The sub is low enough that localization is less noticeable and easier manageable.

REW is the norm for measurement software for this situation. I personal use Rational Acoustics for measurement in the outfield but since I have it available, it makes it easier to see what your response look like. If you are inclined with using measuring software, more power to you. Of course, you ears are the final judgement.