I think anything below 60ish hertz is sub bass though, right? Some subs that are tuned too low, may also have compromises on the fidelity side of things, especially if the main speakers are not chosen so carefully in which o compensate. That can also lead to compromises, such as why we may utilize separate subwoofers to relieve the mains in the first place. Often times, while studying the goals often outlined by the subwoofer heads, they are so enamored with the lowest possible bass, that SQ at the upper range of their usage is not even thought of, or mentioned much, at least.
I use subs tuned to the mid 30's. I hear frequencies down to 20hz with them though. Rolled off? Sure, but it seems to coincide what would be a natural roll-off at those frequencies anyway. In other words, with music, a little bass below 30hz goes a long way in a normal sized room.