Planet Audio P8AWK Low Profile 8 Inch Under Seat Powered Car Subwoofer - 800 High Output, Built-in Amplifier, for Truck, Boxes and Enclosures, Remote Subwoofer Control

Built-in Amplifier – Low-Profile Subwoofers that are amplified do not need an external source and are generally very compact

MOSFET Power Supply - With a MOSFET power supply you get improved switching speeds, better performance with less power from the driver, lower gate-to-drain feedback capacitance, lower thermal impedance for higher switching frequencies.

Variable Low-Pass Filter - A low-pass filter is an electronic circuit that removes all the notes below the filter's frequency setting. You will use the Low-pass filter to primarily keep high notes out of your subwoofer(s).

High & Low Level Inputs - A low level (RCA) input is measured in voltages. A high level (+/- wire) input is measured in wattages. Both essentially carry signal from your receiver to your amplifier to your speakers.

Variable Bass Boost - Variable Bass Boost allows you to adjust the low bass within the boost range to just the way you like it.

Variable Gain Control - The gain control is not for adjusting volume. It simply adjusts the amount of signal that is coming from your receiver and going to your amplifier.

Phase Control - Phase control lets you adjust the speaker phase with the amplifier depending on the location of the subwoofer. This will avoid possible sound cancellation depending on the setup.