How do small woofers produce large bass?

+1 for ProAc slim towers.  I have the Studio 148s and easily go down to 25Hz and can compress the room with punchy bass from AV sources with their 2.5 way config.  ProAc DT8s are similar to this in a 2 way config.  Both use 2 6.5" drivers.  Even better if you get some Dayton Audio outriggers (look exactly like the ones Soundocity sold), which I use with the Rockville Isopad underneath them.

OP:  Thank you for the correction, I must have read the wrong speaker specifications, my apologies!! 

Alot of them. You'll have longer travel move faster more responsive less maSs.happy listening

Tips are tax free this year.that should get the party going

The most important number to look for is the first number in frequency response. This is measured in Hz and the lower the number, the deeper and more bass the speaker will put out. The size of the speaker box, the design of the speaker box, the woofer material and weight and the crossover design change when moving from one speaker to the next, all affects the bottom line...the bass frequency response lowest number. I used to be worried about woofer size, whether the speaker was ported, sealed or uses a bass radiator, and id forget the most informant number....thats right, how low the bass frequency goes. I bought a set of JBl 4333s with 15 inch woofer, ported cabinet and the most basic of crossovers. I thought these were going to be the bass heaven I was looking for. Nope, the response started at 35hz and the open ported design didnt let air really move the woofer until higher volumes. Jbl tried to make up for this by installing huge magnets on woofers, but to me, the speaker was usless, as I did most of my listening below concert levels. My next speaker was the B and W 801s2, which had a ported cab with reflex tubes and a 12 inch woofer with a 25lb magnet. These lacked in bass as the bass frequency was over 35hz. I fixed that issue by ordering the recommended bass alignment filter, which lowered the response to 20hz. So in this case also, the lowest response number is the answer. My speakers now are the infamous amp killer Infinity kappa 9s with dual 12 inch woofers These are sealed cabs that are tall, thin and sectioned off, making airflow to move woofer hard to come by. Infinity solved this issue by making these low impedance, requiring a high current amp to move and return the woofer under control. So even at low volumes, the high current sent by the amp, allows a ful, deep bass that goes down to 27hz. From low volume, to mid volume to high volume, the kappa 9s produce the best bass ive heard in a speaker. I use a 500w amp for the woofers and run them on extended mode, so they thump. Not as dynamic, hit you in the chest bass the jbls and klipsch chorus, but the kappas dont suffer from a lack of bass in the low volumes. So lesson for today is the answer you are looking for, without confusing variables, is to look at the frequency response and any number below 30 will get you thumping properly. Numbers above that, and you might want to add a subwoofer or you listen to music where bass isn't important like country or classical. NOW.....there is an exception to the rule that I fell for, and ended up getting rid of the speakers, as the low bass frequency number was deceiving. That was with the Polk brand SDA 1speakers. They used 2 6.5inch speakers for the bass and had a 12 inch bass radiator. They advertised bass frequency at an astronomical 13hz. When I hooked them up, the bass was low, but boomy as that passive radiator design had loose weak rubber surrounds that caused the cone to flap around have excessive movement not associated with tight, crisp controlled bass. The trick polk used was to advertise the super low response, but not linear to the rest of the signal! Meaning they took measurements many decibels lower than they should have. If they waited for the signal to become linear or flatter, the bass frequency number would be much higher. So they took bass  measurement to early in the signal to juice the specs. Again another speaker i had to learn the hard way on. Sold them after a year or so. I know answer is detailed and may be confusing, but the spec numbers nd the audio scope readings dont lie and show that you can change variables in cabinet design, woofer size, number of woofers, and crossover points, causing a change in bass frequency response, but the actual number and how low it is is gives you the answers you need. Lower equals better. So always look up specs if unsure about bass quality, fullness, and depth. Beats buying and selling many speakers to trial and error them. While ive had ears on many of the better offerings of multiple brands, I could have saved time, money and dissapointment of lack of bass quality I expected out of my speakers.