Imo its easier to distinguish spl because its what you do hear that shows that type of sub, whereas an sq sub its more about what you you dont hear that is present in other subs.. im not sure about tasting the bass, but hearing vs feeling seems like an ok description. Its also about how well the sub can transition from low to high notes at different speeds. XBL and frequency range are good specs to look at. Sq goes beyond just the sub, youd also have to be picky about what amp, box, and wiring is used. It also depends on how much power you want, its easiest to find sq in the 500-750watt/per sub range:
~500watts - Soundsplinter rl-p
~750watts - Incriminator Audio Flatlyne
~1000+watts - 04 RE XXX (more sql, but whatever)