Why the fascination with subwoofers?

@noble100 -- 

I'm not a Bass-Head but I admit I enjoy the bass weight and power that viscerally involves your whole body in the music or ht. 

I can relate to that - certainly. For bass to be able to be enveloping, effortless and visceral are vital aspects for bass to simply be uninhibited. 

But I also believe in setting the crossover frequency as low as possible so the subs only engage when required for accuracy and not for an artificial general system bass boost.

An "artificial general system bass boost"? I don't see why this would be the necessary outcome of a higher cross-over between the mains and subs. One may have a wider frequency span to adjust bass level and overall response, but to me - using an 80Hz cross-over - the goal is the same compared to using a lower XO: for the overall integration to be smooth and seamless. 

Perhaps one of the issues of using a higher cross-over point, apart from it being potentially problematic using several subs scattered throughout the listening room, is the thought of using a high-pass filter over the main speakers. This is understandable, I've been there myself, but I can attest to the positive outcome using a quality digital XO over the mains, and that any detrimental effect on transparency with a proper unit is perceived as zilch. Some may bark at this and claim such a component will inevitably have its say on the sound, and they may be right, but to which degree and in what context? Using a quality digital XO over the mains and high-passing them at at least some 80Hz have a plethora of other advantages that can easily (more than) alleviate a theoretically negative effect a given component may have being added to the chain:

WIN # 1)  Since you are now NOT putting in 20 Hz - 80 Hz into the mains you are not using up the available LF cone movement with bass, so the LF cone in your mains is able to play its higher freqs (up to IT'S crossover point) much more cleanly. You get an apparent 6dB or more dynamic range. You can play your system LOUDER, and also with less compression distortion in the LF driver when you're having that Saturday night dance party and you're playing urban bass technopop at 110+ dB. Really.

WIN # 2)  Since you are not putting bass into that same driver you are not Doppler modulating everything between 80 and 600, or whatever the next crossover point is. This means cleaner mids. By far.

WIN #3)  You are not sucking current out of your main power amp at low frequencies, so there is more current reserve to play those highs louder...

WIN # 4)  Since the cones aren't moving as far at the low freqs the driver itself is not generating as much back EMF therefore the damping factor and all of its issues are greatly negated. And you don't need to run silver plated cold water pipes to your mains as speaker wires because there is less current draw by the speakers.

WIN # 5)  Freqs below 80 are now NOT causing transient intermodulation distortion with the higher freqs (and vice versa) in your power amp. Cleaner still.

http://www.soundoctor.com/whitepapers/subs.htm

I've also discovered that bass quality is vastly more important than bass quantity. A leaner presentation without much extension is preferable to me than lots of bass if that bass is thick, colored, and sluggish. If the bass isn’t well reproduced, I think most would agree we’d rather not hear it at all. The poor bass performance becomes a constant annoyance and a reminder that we’re listening to a reproduction. 

Agreed.

I've learned that realistic reproduction of the majority of the bottom octave (16Hz–32Hz) doesn't require large woofers in large enclosures, 4 subs with 10" woofers in relatively small enclosures are equally capable. 

Equally capable compared to what? There are many iterations of using only a pair of subs that involves 21" units (or bigger) and/or horn subs that would leave 4 spread out 10" direct radiating subs sounding close to malnourished. Would 4x10" be sufficient in many listening rooms to many listeners? I believe so, definitely, but others would disagree, and it's not necessarily for them being "bass heads" as such; what is "realistic" to you may not be the case with others and their setups. 

It's also true that a system’s bass presentation affects such seemingly unrelated aspects of the sound as midrange clarity and sound staging. Thickness in the mid bass reduces the midrange’s transparency. A cleaner mid bass not only makes the midrange sound more open, it also lets you hear more clearly into the extremely low frequencies. Moreover, extending a system’s bottom end has the odd effect of increasing soundstage depth and our overall sense of the recorded acoustic, even on music with minimal low-frequency energy.  

I concur, only to add that these advantages are potentially more pronounced using a high-pass filter over the main speakers, for reasons outlined above. 

However, I'd suggest choosing subs designed for musical accuracy, not home-theater fireworks. Some subs exist to produce the highest possible sound-pressure-level at the lowest possible frequency for playing back explosions in film soundtracks. Others are crafted by musically sensitive designers with high-end sensibilities. Be sure which kind you prefer and are selecting.

I don't find musical accuracy and "home-theater fireworks" to be mutually exclusive. Watching Blu-ray movies I simply notch up the bass level by some 1.25dB's (some may prefer even higher HT-boost bass level). This "amalgam" of proficiency with regards to both music reproduction and movie playback I find is no doubt rooted in the specific topology, namely horns (a pair of 15"-loaded tapped horns, in my case). Horn subs deliver the most musical bass I've ever heard in being more refined, smooth, enveloping, dynamic and effortless than any direct radiating solution I've heard. Horn subs vibrate the air in quite an omnipresent fashion that gives the bass a floating quality even that's rather unique.  No multi-use of direct radiating subs can achieve the same, period, and predominantly it has to do with how the cone couples to the air. Horn subs take up space, though, and 20 cubic feet for 20Hz reproduction may be a hindrance for many, if not most audiophiles. A shame, really..

@atmasphere --

This statement is false. If you encounter a standing wave, it often cannot be fixed with only 2 subs. And it can't be fixed with room correction or room treatment.

Now if you **don't** encounter a standing wave then its all good. But in many rooms a standing wave is highly likely- unless the room is irregular in some way. But any rectangular room will have a standing wave which will be a different locations throughout the room depending on the frequency. In such cases while that bass might be good at the listening chair for certain pieces of music, it may not for others. This is a simple fact of physics.

With a distributed bass array this problem is solved. 

There's nothing categorically false with poster @rauliruegas statement; you CAN have bass that is accurate, detailed, smooth, natural and effortless with two subs, end of story. Both room correction and -treatment can do wonders here, I find, and can (and should) be used sparingly for a successful outcome. Honestly it's becoming trite hearing the constant babbling about what a pair of subs can't, and the double count can. We know by now - 4 subs can be a hoot, and they ease up on the need for PEQ, definitely not trivial. Moreover, all things being equal a double-up in sub count gives a theoretical 6dB's more headroom, and I can certainly vouch for the importance of that. 

You could however take a pair (or more) of bigger, more sensitive subs placed symmetrically to the main speakers, horn load them even, and have a different kind of awesome with other advantages. I know, size is banned in audiophilia, but the simply fact of physics, to use your own words, also has size as a main priority that numbers can't alleviate. Big subs in high numbers, however..

And what's the issue and argument made with smooth bass coverage over a wider listening (position) window? One sub is a narrow sweet-spot, two is wider and so forth, and while a single sub may boarder on the head-in-a-vise sweet-spot, two is definitely good for a pair of listeners to have decent coverage. I don't know about you guys or ladies, but mostly I tend to listen to my setup by myself (and if not I give the other listener the sweet-spot, usually placing myself on a chair behind and to the side of the listening sofa), and I don't need for bass to be swell in every goddamn place in the listening room; the listening position (with room for two, if need be) will do just fine, thanks. Actually this is mostly dictated by the main speakers; I would never listen seriously any other place than smack in the middle between the mains, but that's just me.