well, two 12" subs ported would need about the same air space as a single 18" give or take. The 18" could take more, but it can work in 5cu ft. 4-5 cu ft sealed. Space will balance out for either
Power handling, that all depends on the sub(s) you choose. As for which would be louder, you'll have to pick the sub(s) to determine that as your excursion numbers will play a big factor in that calculation. Surface area is pretty easy to figure out. 226 versus 254 sq inches giving the advantage to the single 18" If the 18" has equal or more throw, then it wins there, too, giving the 18" the win all the way around. (for throw refer to Xmag of the driver, or Xmax if that's not available.)
I am thinking about two hdc's because I know they can take 2600 on a burp each sub and I can still set them up for daily if I get the right voice coils
a pair of dd3512s would be great on 5k. d1ohm coils would give great wiring flexibilty too...1ohm daily, 0.25 burps.
in addition to cone area and excursion...look at motor force per sq inch cone area. also, 2 coils will handle 5k easier than 1 and stay cooler longer for daily playing.
dont know if a 1 18" hdc will be able to handle 5k for burps though it shud be able to since its only 3 seconds but u shud email DJ for some advice to be sure before u buy ......
yes a single 18" has more surface area than two 12" subs. 226sq in vs 254sq in, more or less. The Xmag of the combined 12" vs the single 18" will have an effect as well.
disreguard this thread I decided to stay the sq route....the good thing is I bought a hifonics 2607 rated at 2600 and ive read around and it does do rated power but not all of the amps they make do so ill have plenty of clean power for my image dynamics idmax 12 rated at 1000 rms
the issue with hifonics was that they rated amplifiers using an unregulated power supply at 16 volts. The amps will produce rated power, but at 16V, not 12 or 13V as most cars actually supply.
I read people got the rated power on this amp at 14.4. when i get the amp installed ill get my brother to run the amp on his true rms meter and post results