XD600/1 - JL Audio 600 Watt Class D Monoblock Subwoofer Amplifier Monoblock Subwoofer Amplifier Differential-balanced with RCA jack inputs State-variable, 12 dB/octave Butterworth or 24 dB/octave Linkwitz-Riley with continuously variable cutoff frequency selection from 50 - 500 Hz (defeatable). Buffered pass-through type 24 dB/octave Butterworth @ 30 Hz, defeatable