If we are referring to subwoofer mid bass Id think most of us cover 60/120 give or take 10hz. . If the op had asked about midrange that would have indicated the upper limits of most subs and since it was about subs I probably way overreached in assuming he was speaking about subs.
Anything below 500 Hz is bass. If you play with a sharp low pass at 500hz, speech is virtually unintelligible. It is clearly bass and that is all when you hear it.
So really everything from 100 Hz to 500 Hz is really midbass, or just plain bass if you like.
The bulk of the power is 100 Hz to 2.5 KHz, especially from 100 Hz to 1.5 KHz. That is about 80% of the power band.
So as I keep saying a sub off loads an amp or receiver hardly at all.
A properly balanced speaker that has a well balanced response to 50 to 60 Hz does not sound bass deficient and most would assume there is a sub in use. The problem is finding properly balanced speakers. Adding a sub is all too frequently a work around, and really only essential if you want to shake the floor.