Soundstream T1.4000DL is an amplifier with a Low Pass Controller that adjusts the frequency response of your subwoofer upwards and is continuously variable from 40Hz to 220Hz. It also has a Sub Sonic Controller that eliminates the lowest frequencies to protect the subwoofer from damages. These low frequencies can cause damage. The frequency is adjustable from 0 to 50Hz. Additionally, it has a Level Controller that adjusts the input sensitivity from 6 Volts to 0.2 Volts. The Input - RCA Inputs accept line level(RCA) inputs from 0.2 to 6 volts.