Bass refers to low-frequency sounds from 20 Hz to 160 Hz. Sub-bass frequencies start at 60 Hz and drop down to about 20 Hz. The sub-bass level is the level at which you will feel the bass more than hear it. For subwoofers, the lower the frequency, the lower the bass. The best bass range for most subwoofers is from 20 Hz to 120 Hz. Any lower than 20 Hz is out of range of human hearing.
One thing to consider is sound quality and accuracy. As you go lower on the frequency spectrum, the quality of music can dip. If you just want the loudest, deepest bass possible, that isn’t an issue. But if you want to listen to the music as it was intended, you may want to go a bit higher with the frequency.