size of the driver

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).

Excellent insights from Drew, as usual. On the question that Bombaywalla raised about 3 db vs. 6 db, I believe that despite the apparent disparity you are both essentially correct.

For a given drive voltage, the total radiated acoustical power will be 3 db greater if there are two paralleled drivers as opposed to one (everything else being equal). Addition of the second driver will double both the amount of electrical power that is drawn and the amount of acoustical power that is radiated.

However, at a listening position that is approximately equidistant from the two drivers there will be a 6 db increase in SPL, as a result of constructive interference. At some other locations destructive interference will occur, resulting in low SPLs. Averaged over all space there will be a 3 db increase.

Best regards,
-- Al

Some have argued that larger drivers will have greater energy storage, and correspondingly slower energy release.

>04-30-12: Unsound
Some have argued that larger drivers will have greater energy storage, and correspondingly slower energy release.

They don't store energy and ring longer. Ringing at resonance is purely a function of driver + enclosure Q.