I am also making a DIY subwoofer with the 12 inch IWAI driver, I have decided to go with sealed as my room is small with about 100 sqft. and there will be room gains, so it will sound good enough I guess, as for the driver, high price does not always mean better performance, and the bigger the driver the better the low end is somewhat true, as an 8incher wont be able to physically match the amount of air a 12inch would be moving, considering they both are of similar specifications ofcourse.
I have already ordered the driver, will probably get somewhere around next week, and then 200 watt plate amp and a sealed enclosure from albin is what I have planned for now.
I have done quite a research on subwoofers in the past few days, I will try to answer your question one by one.
1. Should we go for ported or sealed?
Since your room is small, a 12 inch sealed would be enough, as there will be room gains, but then again going ported will enhance the extreme low frequency that can be good for movies. The issue arises with size mainly, as going sealed you can manage with a 45L enclosure, but going ported you will require a min of 65L to take advantage properly. Also, add to it the complexity of building, you will have to calculate the port dimensions and everything , which could mean that there are more chances of going wrong, you will need an excellent builder here to precisely mange the volume, port dimensions and length. You can use softwares like WinISD or Subboxlite, to design and check things.
2. Is very low frequency extension good (20 Hz and below)?
We humans cannot hear frequency below 20 Hz, going below that would mean basically the driver will move the air, you may not hear it but you will feel it. For music it is not required, for movies yes it will enhance the experience.
3. One or two subwoofers?
two subs will always have more power, but for 150sqft I don't think you would need 2 subs if you are going with a 12incher. Also you cannot have ported and sealed sub together, it has to be ported + ported or sealed + sealed.
4. 10" or 12" or larger (our music room sizes are probably roughly around 150 to 200 sq ft)
12" is the sweet spot, just go with it.
5. How much impact the driver has on the quality? So IWAI, Pioneer or SB acoustics?
You can simulate different drivers with WinISD and Subboxlite, each driver requires different size of enclosure to perform optimally, generally what I have noticed is that costly and better drivers can go low with small enclosure where as cheaper drivers need bigger enclosure to achieve that same freq.
Avoid any Car Sub, their driver require a very large enclosure, they are made specially for cars because they take advantage of the car cabin gain (room gain).
6. Class ABCDEFG (what kind of amp) to drive the driver
There are few options here, you can either go with Plate AMP, those are Class AB, or you can go with the likes of Fosi that will be Class D, now both should sound good, but AB will have more power.
7. Crossover details
If you are going to use your computer to drive these, then you can use VoiceMeeter to set the crossover, otherwise you should look for an amp with crossover settings, most plate amps provide that, and well the setting would depend on your speakers.
8. Any recommended builder?
These are some builders that I have come to know about
AlbinTech on youtube
DiptiElectronics on youtube
Audiofy.in also provides
I personally am waiting for my driver to get home first, so I cannot vouch yet.
Attaching specs and dimensions for IWAI, as you cannot find these on official page yet, you can use WinISD and similar apps to compare.
If you need more help or anything you can DM me, Good Luck.
