size of the driver

It turns out the large woofers of the '60s and '70s were counterproductive to bass extension, driver blending, and the distortion of cone breakup.

Smaller drivers solve many problems in dispersion and driver integration. A 12" woofer starts beaming (i.e., no dispersion to speak of) at 1100 Hz. A 6.5" driver doesn't beam until about 2100 Hz, making it much easier to blend with a tweeter. A 6.5" driver will also accelerate and stop faster than a 12' one, and it's easier to make a 6.5" speaker that won't have significant cone breakup at full excursion than a 12" one.

Great strides have been made in cone excursion. A 6.5" driver with 1/2" excursion can displace more air than a 12" driver with 1/8" excursion (typical of a '70s woofer). Twin 5.25" woofers with 1/2" excursion have 50% more potential displacement than a 12" with 1/8" excursion.

Then, as was mentioned before, you get better dispersion and therefore better in-room power response with a narrow baffle than a wide one. So all in all, smaller woofers make for better overall speaker systems--better imaging, better dispersion, faster response, higher crossover points without suckouts. The Atlantic Technology AT-1 manages to get <30Hz bass extension from an MTM arrangement with two 5-1/4" woofers and unique cabinet loading.

Driver size has nothing to do with "fast" or "slow". Twice the motor strength will accelerate double the mass as a smaller motor/mass combination whether we're talking about vehicles or drivers.

More or less true, but bear in mind that a 12" woofer has *at least* twice the mass of a 9.5" woofer, and perhaps more because it will probably have a thicker cone to counteract breakup. All things being equal (which they're not), a 12" woofer has 3.5 times the mass of a 6.5" woofer, so by your reckoning it would need a magnet 3.5x as powerful.

>Bigger drivers can still have that old school sound. Bigger drivers move more air but tend not to be as accurate and have trouble keeping up with a 5" midrange so you can loose cohesiveness.

Nope.

Maybe, maybe not. However, speed aside, the the large driver still has a disadvantage in driver blending because its dispersion pattern turns into a beam at a lower frequency. A 12" cone starts beaming at 1100 Hz; a 6.5" at about 2K Hz. Guess which is easier to cross over to a tweeter at 2K Hz while maintaining uniform dispersion?

Drew, I agree more than disagree. Dispersion can definitely be modified with waveguides and phase plugs, and beaming can be mitigated with 1st order crossover slopes. Large diameter woofers can be just as fast as small ones if they have the magnet strength and cone stiffness.

Still, if the issue is why 5.25" and 6.5" woofers became the de facto standard over the 12" woofers of the '70s, it's probably a combination of manufacturing costs vs. performance and WAF. The old oversized bookshelf speakers of the '70s had no WAF whatsoever and the bass extension (especially of the JBL L100) wasn't so great either. The PSB Synchrony 2 is sexy with a narrow footprint and has flat response down to around 36 Hz.. 12" woofers can kick ass, but not in a 2.4 cu. ft. enclosure; a pair of 6.5" (a la ADS 810) do better in that same oversize bookshelf enclosure; many 12-inch woofers need about 4.7 cu. ft,, at which point you'll hear some *serious* bass.

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."

05-01-12: Drew_eckhardt
04-29-12: Johnnyb53
>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

"Violent" isn't a problem until you reach the linear or physical limits which geometry dictates you do when using such small drivers.

>And you base this opinion on what?

I draw upon personal experience with speakers including transmission lines built with similarly small drivers...

Drew, it's pretty obvious I was responding to Tamule1 and not saying anything concerning your previous statements. I question his setting a size definition on woofers that essentially excludes 90% of them. A driver doesn't have to function well as a subwoofer in order to be a competent woofer.

Your enthusiasm for larger drivers is already well known. You play down the disadvantages of the flex and weight of a larger diaphragm, the cost and bulk of a larger magnet structure, the dispersion enhancement of a waveguide (I've yet to see a waveguide on a 12" driver to turn it into a midrange) while pointing out the disadvantages of longer excursion, small radiating area, etc. of smaller diameter bass drivers. It's really a matter of picking your poison.

If cost, size, and weight are not important factors, fine. Knock yourself out and put in 12" and 15" drivers. If WAF, floorspace, and bass speed at affordable prices is important (and it's intuitive that this package is an easier sell to both sexes), then the narrow column anchored by multiple 6.5" woofers rules. And that's why they dominate the sweet spot (not the highest end) in high performance loudspeakers.

Waj4all:
After all, the headphone (just as the small speaker) measures flat thru-out its frequency-range, as is apparent in close proximity (i.e. clamped to the ears). But then, any distance between the 'phone and listener causes it to sound more like a tweeter. All frequencies are being reproduced, but the small surface-area of the 'phone's drivers is incapable of coupling enough air to transmit the lower frequencies (i.e. below treble) to the listener.

Yes. it comes down to coupling the bass output to the room size. Even a pair of Wilson Alexandria XLF's would sound bass-shy outdoors. Perhaps preferred woofer sizes are related to customary listening room sizes.