Small drivers vs big drivers

Driver size has nothing to do with the frequency it can play. 20hz is simply the driver moving back and forth 20 times per second. 

Size does matter how far the drive has to travel to make the sound loud enough to hear. Pressure being a function of force x area (force being mass x acceleration etc). 

So a large driver needs to travel a lot less then a small driver for the same Sound Presure Level. 

Large drivers have trouble playing high frequencies do to not bring stuff enough to move 20,000hz without flopping around like a flag in the wind. Not to mention they will beam due to the sound wave length being shorter than the surface area creating it. 

Look at headphones. They have great bass from a tiny driver. It however only has to play that bass very quietly due the sound not needing to trave very far (the “room” is also tiny)

when small drivers travel far there is a lot of bending force on them from the driver surround. The voice coil also needs to travel farther and stay aligned. Then there is the electrical issue of long travel but that if for another day. 

Many good points. All tech stuff aside, I had a pair of jbl 250ti's for many years. They were a 4 way speaker with 14" woofers. I sold they recently and bought a pair of Revel Salon 2's with 3, 8" woofers.The Revels are  better speakers in every way except dynamics and base impact which is not a small feature. If you like the live sound of rock, the jbl's were hard to beat. Also, with the sensitivity the jbl's they played very well at low volumes. I did miss the bass impact of the jbl's, so I added a JL sub. I do love my current system, but the was cost was crazy. I may have been able to make a better choice in speakers, got the best of both worlds and kept my cost down (perhaps Legacy). But higher end speaker comparison is difficult because of the limited distribution.     

I am fortunate to have extensive experience with both, but every ~ multi ~ 4" driver speakers I’ve ever heard needed subs. However, I had a 7ft pair with ~ 8 x 6.5s which went plenty deep

I currently own Emerald Physics KCIIs which has a 10" concentric driver plus 2 regular drivers, but their 2.8 series has 2 @ 15" carbon fiber speakers, one being concentric ~ $9K a pair. I hope to have a pair one day soon

bdp24, you and I see many things the same way, maybe because of our being drummers (well, I was, no longer, but my son is, I have the Gretsch 135 set here for him to use when he visits).  Real music, live music, has a weight to it that may speakers do not impart.  I have three stereo systems in the house, and my Vandersteen 5A setup can do the weight very well; system 2, Unifield 3 Mk2, are better for imaging and pinpoint placement; my new third setup, JBL L100 Classic-based, so far seems to be able to do the weight things well.  Must be the big woofers.  

I remember, years ago, at a Steve Earle show at the TLA on South Street in Philly, the music/sound/bass/volume made the pants on my legs move.  I liked it too.