[Josuah]

I modeled the same box with 15" drivers and it didn't give me anything extra. It just costs more and would require a sonotube that won't even fit through the door. Maybe less distortion, but I don't know about that.

I've been trying combinations of 12", 15", and 18" drivers within the same ~700L, in sealed, ported, and passive radiator combinations too. And six 12" drivers in a sealed sonotube seems to be the most cost-efficient approach, and doesn't seem to sacrifice much.

Granted, I won't need 5Hz often, but this project is to give me something I don't already have, i.e. <12Hz, while boosting a bit in the frequencies I already have by adding more drivers and watts. In the end, this single sub might be able to replace the two 16-46PC+ subs. I don't think I'll know until after it's built though. If I try to go for more headroom and lower distortion than what I currently have, that either means doubling up the 16-46PC+ subs which would cost about the same, or replacing them with something like what this project would end up creating.