Description:  The so-called low-pass filter to filter out the human voice board is more than treble part, retain the low  frequency part is amplified to improve the bass reproduction efforts, people will not hear the sound of  musical instruments and high-frequency sound during playback.     Features:  Power supply voltage: DC 9V-32V single power supply.  Dual channel input, subwoofer output, then the output amp|ifier,can not directly connected to the speaker.  The multi-stage filter, better bass effect.  The phase adjustable.  Potentiometer from left to right: frequency adjustment, bass volume control.  The cut-off frequency: 22Hz-240Hz.  Potentiometer shaft center to center spacing: 3cm.  PCB Size: 62 9* 26.5mm.  Audio input: mono or two-channel.  Audio output: Mono(connect with amplifier).     Package included:  1 x Low Pass Filter Bass Subwoofer Pre-AMP Amplifier Board.  1 x Power cable.  1 x Audio Shieklded cable