size of the driver

Coming from the "old school" and being a complete (or almost) novice here - in the old days back in 1970-75 we thought that the big (read - wide) driver will have better capability to produce more realistic sound, talking about lower end of the spectr at least. But nowdays I am seing 6 inch drivers stated as "bass". Just curious how well those perform or in another words what is the secret behind those if they really can perform at the same level as the 12 inch ones?

And another question which I guess is too simple and too basic around here that's why I couldn't find some point to point answer - when we speak about sensitivity - would that be a true statement to say that higher level (say 92-95 db) will allow to extract "fuller" sound spectr at a lower level of volume? My feeling is that with somewhat lower 89 db or less you need to increase the volume in order to have more visible lower end?

Thank you for your time
You can add 6dB for a floor mounted woofer (as in many 3-ways), 6dB if there are a pair of bass drivers, and 6dB at the cross-over point to a sub-woofer....
Drew, why are you adding 6dB? It's power output, you should be adding 3dB in each case.
Back in the late 70s when i sold gear at tech hifi, bass drivers in most
speakers back then tended to range from 8 to 12 inches mostly with the
occasional 18. I levitated towards smaller drivers mostly for better sound
for most with their amps in their applications. Larger drivers were largely
inadequately built and under damped in many cases i heard resulting in a
muddier sound although typically with more lifelike impact. .

I think both amp and speaker technology has come a long way since and
that those issues can be adequately addressed these days in a variety of
ways, with both larger or smaller drivers, if the overall design is good.
Often though size, large or small, still matters though to many sound
quality being just one of the important considerations.
real bass comes from moving a large surface area gently -not a small surface violently . 6.5" is not a woofer size IMO
It is cheaper to make a good small speaker with smallish drivers than to make an equally good larger speaker with large drivers. In addition to the cost of the drivers the cost of the speaker cabinet sharply increases with size. This wasn't necessarily the case back in the 70s before rigid, highly dampened cabinets became common. For cone based speakers if you want low distortion, high SPLs and response down below 40Hz large diameter woofers are the only way to go.

04-29-12: Tamule1
real bass comes from moving a large surface area gently -not a small surface violently . 6.5" is not a woofer size IMO
And you base this opinion on what?

What then shall we call all those 5.25" and 6.5" drivers that provide real bass extension down to 25-30 Hz?

You also left out the part about how the back wave is managed, which accounts for why the Atlantic Technology AT-1 extends usable bass to 29 Hz from a pair of 5-1/4" woofers.

Next thing we'll need a disclaimer:
"No violence was committed in the generation of these low frequencies."