size of the driver

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."

04-29-12: Sounds_real_audio
>If 12" drivers were as fast and accurate as 4" drivers we wouldn't need any midrange drivers.

It's a function of system design. You're not going to beat a 12" midrange paired with a like sized wave guide for sound quality although the 30" high x 15" wide "stand mounted monitor" combining the two may be hard to get past your spouse.

Your brain hears timbre as a combination of the direct sound and what it identifies as reflections with the later coming off the speaker at extreme angles (> 70 degrees for the side walls depending on toe-in).

So to get a natural sound you need drivers to have similar behavior both on-axis and at those extreme angles.

Drivers also become increasingly directional as their dimensions grow large compared to sound wavelengths. By 900Hz a 12" driver has lost 3dB 45 degrees off-axis and by 1400Hz it's 6dB down.

At those frequencies a 1" tweeter on a flat baffle is omnidirectional.

The two won't match like the waveguide does. A 12cm cone or 5cm dome will match on a flat narrow baffle.

>04-29-12: Bombaywalla

> 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.

That's the sound increase you get when you run the drivers out to their physical limits although it'll take twice the power to get there as with a single driver. With the example 5.25" driver I listed 2.83V (1W into 8 Ohms or 2W into 4) will get you to xmax at 80Hz with one driver or a pair in parallel with power around 0.25W for a single driver and 0.5W for a pair (impedance increases as you approach resonance so power drops).