Whether a standard model is used or some kind of hybrid, the bass is good and most people don't augment their speakers with a sub. Room gain tends to lift the very deepest bass, so a gradual rolloff is desirable in many cases. However, in large rooms or in other situations where a sub is desired, one of the dedicated subwoofers can be used.

Dedicated subs are tuned differently than a full-range model. The woofers chosen for the subs are designed to be used between 20-200Hz, and the cabinet is tuned for this range also. In contrast, woofers chosen for full-range models are designed for a much higher bandwidth, but don't go as deep.

If you need a midwoofer to go from say 40-400Hz, then the bass bin used in a three π or four π is perfect. It sounds nice in the midrange and bass goes pretty deep. Rolloff is gradual and smooth, making it a nice compliment to room gain.

On the other hand, if what you're interested in is to augment the very deepest bass frequencies, then a subwoofer is better. It can be used down to 20-30Hz. A dedicated sub should be crossed over no higher than 100Hz for best integration. Any higher and you will be able to hear the sub as distinct speaker, which is not what you want. You want a subwoofer to add a foundation, but not to call attention to itself. It should not be louder than the rest of the system, nor should it "thump". If done right, no one can tell the subwoofer is on, it just sounds like the mains go deeper in bass.

Thanks again!