A subwoofer with its own power amplifier built into the cabinet. Subwoofers require a lot of power, so the amplifier will typically be at least 300W and range all the way to 1500W in the highest performance models.
The subwoofer power amplifier will typically also include several controls like gain/volume, phase, low pass filter, etc.
SVS subwoofer amplifiers also have sophisticated DSP control for improved sound quality and refinement under all conditions and also a wider range of menu options.
Every model in the entire lineup of SVS subwoofers is powered.