How do small woofers produce large bass?

@audiotruth wrote:

I listen to probably 80% home theater and 20% pure two-channel music of all sorts. I am contemplating upgrading the speakers ...

...

... I am baffled as to how the 6.5" drivers in all of these new speakers are going to produce home theater sized bass. I’ve watched every video, read every article about those 4 contenders (above) - and everything/everybody says essentially "no worries, the woofers are lighter and faster, and since there are two of them, they make a great deal of bass. I just think I’m not seeing the "science" or "physics" of that. Like how are these 6.5" drivers going to handle something incredibly powerful/dynamic (bomb blasts/gun shots/thunder/explosions etc etc??? I’m afraid I’ll be let down by something like the PSB T600’s or the KEF R11 Metas when head to head with the dual 8" drivers in my Arendals. ...

You’re definitely on to something, and my advice would be for you to stick with your gut feeling about the physics requirements. With that in mind:

Given you’re apparently much more invested in home theater vs. music (80/20%), I’m surprised to see you single out speaker items that are, how shall I put it, on the anemic side physically and more exclusively linked to or associated with two-channel music reproduction. Have you investigated into speakers like JTR? Their home theater series appear to be addressing what you may be after and aren’t shy in the displacement and efficiency side of things which, from my chair, are equally important with both music and home theater use. 

It’s interesting, not to mention sometimes infuriating seeing the lengths marketing departments will go trying to convince potential buyers that small sized woofers and speakers overall are close to the equivalent of the second coming. To my mind anything below 12-15" shouldn’t be called a woofer, although much smaller drivers for domestic use are nevertheless used as exactly that with low fs, low efficiency and all to suit a small physical framework and still wanting fairly deep extension - with all that implies.

Small size in speakers isn’t a design incentive brought forth with the primary intention to what suits or accommodates good sound; largely it’s about selling speakers more easily while invariably being faced with the obstacles small size produces, and yet it’s almost being sold off as the opposite: an advantage. From a buyers perspective, why would you fold to such a claim with little to no basis in physics? 

In audiophilia size of speakers has become incredibly expensive. Small 2-way stand mounted speakers easily cost north of $10-15k/pair (ridiculous when you think of if), turning their larger floor standing brethren into very costly affairs - and even they rarely accommodate physics in a desirable fashion. This, among other things, is the primary reason why I’ve looked elsewhere for years, i.e.: in the direction of the pro segment of speakers to gain both size, efficiency and developments in driver design at a considerably lesser price than anything found in domestically oriented products that would even attempt a similar feat (usually with no success). 

@phusis 

although much smaller drivers for domestic use...little to no basis in physics

I would't disagree with the possibly of using HT speakers in this application. But I disagree with people using the term physics and science as if it's a complete equation.

A 12-15" HT driver can be room overload for many homes above 80Hz. Thus to get the most clean and beautiful sound for mid-range and music with the lease room mode, smaller drivers could be more appropriate.

I was using 2 SVS SB2000 subs, I really like subs. Then I upgraded speakers to Canton Vento 100 uses dual 8” woofers and rated to 20Hz. I’ve removed the subs as they are not needed honestly. 
My room gets pressurized as much as before. 

@josepad is that marketing? Secrets shows bass starts to fall off at 37Hz. My B&W 802 don't have the xmax to move anywhere near as much air as even a single 12" sub, no pressure. The surrounds on the Vento don't look much different. Subs on the other hand have a more durable and longer throw surround.

@bartsw 

Not sure I understand your reply. What do you mean by marketing? We don’t hear anything below around 25Hz, it’s not about that. It’s about feeling and sustain of low notes. The SB2000 are rated down to 19Hz, so again it’s about feeling and low note sustain and room pressure. 
Also remember your gear needs to be able to replicate that low frequency range.