Twin asymmetrical loading sub is designed for optimized output for limited size, (Curve in red is SW212, Curve in green is SW115 vented sub, they are in very similar size).

SW2 series use two woofers per cabinet therefore power handling is doubled, along with the extra 4dB more in sensitivity, SW212 can output at least 7dB more sound pressure than similar-sized SW115.

If we compare SW215 with SW118, we will draw a similar conclusion.