For flat response, 70 to 115 liters tuned to 40Hz is best for the JBL 2226. You can put a 2226 in a larger box using an ELF alignment for deeper bass, but there are other drivers that are better suited to subwoofer duty.Then again, the 2226's are pretty sweet, and making subs out of 'em wouldn't suck. It's just that you'd probably want to use 2235's or 2245's if you had the choice, and use 2226's as midwoofers instead.