My Reference 3A Veena II Towers use a single 7" mid-bass direct coupled driver in a 39" tall tower. At the SPL's I listen too in my townhome they provide plenty deep, clean, articulate bass from my Bryston B100 SST integrated amp...at just 10 watts. The same size driver in the Energy Pro 22 Monitor large standmount speakers I gave to a friend was able to get into subwoofer territory lows to 28 hz
@ - 1.5 db's. Both drivers were in rear ported, Rigid, Fairly large cabinets relative to the radiating surface of the drivers.
For my 6.1channel home theater system, A single Energy S10.3 200w sub gets down to 21 hz @ -3 dB's using a 10" driver in a ported cabinet.
The 4" mid-bass driver in my Realistic Minimus 7"s produce minimal bass operated flat, As expected in such a tiny cabinet. But with the EQ on the matching STA7 10 wpc receiver switched on produces satisfying bass for a bedroom or office without the need of a small sub. They might make good desktop monitors with the matching receiver too.