One big subwoofer or two weaker subwoofers?

Size matters. Of course so does quality, but 20 Hz sound at any reasonable volume is an uphill battle for an 8-10 inch driver.

It is possible to make a small cone vibrate at subwoofer frequencies, but what happens when the sound goes out into the room? It spreads out and becomes less loud. And with a small driver, the SPL falls off rapidly. If you have a small room, and listen close up, a small subwoofer is OK. In the extreme case, tiny earphone diaphrams can reproduce LF very well, but require immediate proximity to the ear.

Take a look at what the cone of a small subwoofer is doing...long excursion is necessary. For any dynamic loudspeaker, (good ones and bad ones alike) performance deteriorates as cone excursion increases. A large cone will need much less excursion to move the same volume of air.

In keeping with rules of full disclosure, I state that my SW system consists of three 15" plus three 12" drivers mounted in large sealed enclosures embedded (for cosmetic reasons) in the wall of my room. These systems "drive" the entire room, so that the sound is very uniform throughout, and there is an effortless quality that I miss with even excellent smaller subwoofers. Ideally, I would have the entire wall consist of drivers, and it would not matter if it was 20 15" cones, or 120 8" cones. My subwoofer design philosopy is consistent with the nature of my main speakers...three planar MG1.6.

Eldatford: interesting! But if your drivers are IN the wall, why have you sealed them?? Why not IB? Or am I missing s/thing?

BTW, is that 6 low frequency drivers per channel - or is it ONE s/woof (with 6 drivers)?
Pls excuse my confusion.

The SW systems are in the wall because I like the characteristics of a sealed (acoustic suspension) system. There are many drivers suitable for sealed box alignment, but few designed for infinite baffle operation. Also, it is an outside wall.

It is three separate SW systems, each having 15" and 12" drivers. Each driver has it's own amp. This is necessary because the 4 ohm driver impedance discourages parallel operation. Each 15" driver is powered by half of a CarverPro ZR1600 digital amp, 600 watts. The 12" drivers are powered by 250 watt SW "Plate amps" and their signals are equalized for phase and frequency response. I intend to use the 12" drivers to tweek the overall system performance, but in practice little or no equalization is needed. The enclosures are about 7.5 cubic feet each. The front baffle of each enclosure (which resemble coffins standing on end) is covered with acoustic foam to absorb some of the back radiation from the Magneplanars. The whole SW system is concealed behind fabric wall covering. In spite of its massive size, it is nearly invisible. (WAF you know). At present I am using 80 Hz 24 dB/octive for crossover. This makes life easy for the Maggies.

Because I designed and constructed the whole thing it didn't cost too much. I reckon it was about $3200, including 2550 watts of power amps, and sheetrock, plaster and paint to remodel the living room. Besides, the project was interesting. Better than dropping $3200 in a one hour visit to an audio shop.

if you really beleive 8-10 inch is faster than 15 -18inch..your wrong....8-10 quality is better than 15-18 crap' but 15 18 sota, come on !!!!If your room is big enough...if you are using monitors than 8-10 is better

Mavilla, are you really considering different subwoofers or did you start this thread just to see the blood? :-)