Theoretically, 2 12s will get louder than 3 10s. On top of that, 4 10s would get louder than 3 12s.
But the difference in sub size also relates to where the drivers will be most efficient. A 10" will tend to be as efficient or more efficient at higher frequencies, and at that point if you were to have equal surface area between both sizes, the 10s would typically get louder due to where their efficiency lies. Likewise, a 12" would be more efficient down low, thus be louder at that point.
This is the same reason that ported is "louder" than sealed. It isn't because ported is louder at every frequency, but because you are extending the bandwidth down low. With a typical subwoofer in a sealed box, Fc (resonance of the system) will occur somewhere around 50hz, and begins rolling off around 12db/octave below that. Where, with a ported box, you will typically maintain a flat response down to the tuning frequency, or at least somewhere near the tuning frequency, and see a higher order rolloff below that point (24db/oct or above). When taken over an average of the bandwidth, ported enclosures will average somewhere around 3db louder (but is not always 3db louder at a specific point, sometimes more, sometimes less). A simple plot in WinISD will show you this.
"That confused me a little. Can you explain what you mean by that? Do you mean in sealed boxes you dramatically lose db's the lower the hz goes?"
Yup, in an anechoic chamber. In a room or a car, however, the transfer function ("cabin gain" in car audio) compensates for this rolloff and provides a relatively flat response sealed. With a ported box, it's extended output down low in combination with cabin gain tends to produce a peak in lower frequencies.
Hm, so your saying a ported box, correctly tuned to a low frequency, should give u more of a deep "feely" bass hit/production than a sealed in a car cabin? I'm referring to like 20-25 hz area.
My last system I used 3 Fosgate punch 2 in a sealed enclosure, my single RE sx15" in a ported enclosure is much louder. Excursion also plays in this factor. Polo..
