The thing is, the smaller the box, the higher the cutoff. You can put a 2245 in a 4 cubic foot box but then it's not what I'd call a subwoofer, with f3 of 50Hz. Best to put it in an 8 - 10 cubic foot box tuned to 30Hz, which gives deep response, with f3 of 33Hz and f10 of 25Hz in a 10 cubic foot box. There's plenty of excurison, so that's not a limit through the entire passband. The thermal limit puts maximum output around 120dB at 1 meter. Naturally, excursion becomes a limit below fl, so high pass at 20Hz.