Bass Driver Size - how much better is an extra inch?

Right, most people (women) do not want big speakers. 

Assuming proper driver design larger woofers can go lower and have less distortion because they do not have to move as far to create the equivalent output of the smaller driver. There is a limit. As the woofers start getting over 18 inches (some say 15") it gets harder to control the motion of the cone creating more distortion not to mention the size of the enclosure gets prohibitive for home use. I think 12 and 15 inch woofers do fine in the home environment. There are 15" drivers now that will work in a 1.5 cubic foot enclosure which is darn small.

Many people notice that for some reason the midrange opens up when subwoofers are added. The low bass gives you a different midrange perspective. If a two way crossover is used distortion in the main speaker is reduced. If a lower order crossover is use enough midrange may come from the sub to change the perspective but I notice this even with steep slopes and we are talking about 10th order. The problem with steeps slopes is the crossover becomes more obvious. The compromise is 4th and 6th order which works great at least in my case. 

Most reference speakers, in the bass/mid-bass area are mid 6-10 mm at the most on Xmax, and higher sensitivity.  If they even address sub at all, other than to roll it off sooner..

Better idea..

Monitors can't do it all well..

Full range speakers are full range speakers, doesn't mean it's a good idea..or that they do it very well.. I cut anything to do with the monitor at  40, no matter.. the set up.. Small monitors (bookshelf type stuff) and no sub.. Just easy on the ol ears that way.. Higher when we add separate subs. maybe 60-80 on the roll off.

Depends on HOW they have it set up.. Biamp able, I disconnect the bass. My bass/sub system is ALWAYS better. 300 hz and down..

Can't put everything in the same box, it can't work.. :-)

BTW every inch counts.. that's X 2 there is a back side of the bass drivers too. Can't just dismiss that... Passive radiators, and ports, make NOISE.. all part of the measurement process.

IB (no port) maybe not, at first, anyways.. The enclosure might.. Depends who made it and how well it's dampened. Panels breaks, are number one in IB structures...

Regards

B&w 802 speakers, $22k, have two base drivers at 8 inches.

to me that still seems restrained. 
Better to have 2 smaller base drivers vs 1 bigger size?

At $16K new, the Revel 328be uses three 8 inch woofers. In room response should be in the 20's and the measurements I've seen show low distortion. 

Honestly, bass drivers should be 8” or bigger in my opinion.  10” or 12” is even better.  Thats why you should just augment the low end with a sub but many 2 way speakers today with 6” drivers produce sufficient bass.

If you sit there though and go up a line of speakers, the drivers get bigger and the sound fuller.  I’ve found that no 5” drivers can cope with the abuse I want to throw at them.  It’s got to be at least 6” if not 7”.  I learned this early on in the Paradigm line.  The difference between dynamics between studio 10’s and studio 20’s was pretty substantial.  The bigger driver on the 20’s vs the 60’s would even play louder.

So yes, with regards to bass drivers, bigger is better!