perhaps an example? maybe kicker, ID....

Acoustic theory tells us that for every doubling of cone area or amplifier output there will be a 3db gain! So this said if all factors are the same on each woofer ( enclosure, wattage, direction etc.)then the extra two should show about a 4.5 db gain total!

but all factors wouldnt be the same, would they? You would be cutting the wattage to each woofer by 3, also, the woofers would not have the same 'specs' as the one 'big' one,
so does that theory still apply?

check out some woofers at local shops, is the best bet. Of course they will try to sell you whatever they make the most off of, but just be stubborn, and dont get the impulse buying bug...

look at maybe a kicker L5 or L7 for the one sub setup, maybe some kicker comp VR's for the three (soo ugly though, lol)
or maybe some JL's

again, I would say just bide your time and watch the for sale section...you'll save BILLIONS...lol

I may have missed this, but what is your budget?

For the 3dB gain for doubling cone area, total power is what matters. I.E. 2 woofers with 150 W each = 3db louder than 1 with 300 (in theory). Specs will of course play a large role.

budget? well hmm...i am 16 and have no job. i still have to buy a 200amp alternator, 2 batteries, 1/0awg wire for everything, plus another hundred on a deck. so i have about...3-400 to play with. i really wanted to do 4 subs but i dont think 1200-1300rms is enoguh to play with. if i have 3 then they will get 400 to each which is pretty damn decent for me. i wanted to get the audiobahns and invert mount them to look wicked awesome. so just say i'm not looking to spend too much.

1200 or so watts will be PLENTY in a daily driven car..

I had around 800 to four 10's in my cutlass and it was deafening.

Just make sure you are amplifying your front stage as well, or else that much bass will totally drown out your music..

I ran 4 cheap jbl subs, and they worked wicked.

If you are looking for cheap, I am a big JBL fan, but thats just me.

also, make sure you absolutely need that big an alternator before you go balls out on one...they can get pricey

try D.G auto electric in the yellow pages, they are great for cheap, big alternators