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 not hear the sound of musical instruments and high-frequency sound during playback. The buyer must understand knowledge of this area. 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 OP AMP: TL072 size: 6.2 x 2.6cm Material: ABS colour: As shown Package Contents: 4 x Low Pass Filter Only the above package content, other products are not included. Note: Light reflection and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.