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 reproduction efforts, people will not hear the sound of musical instruments and high-frequency sound during playback. The buyer must understand knowledge of this area. supply voltage: DC 9V-32V single supply channel input, subwoofer output, then the output amp|ifier,can not directly connected to the speakerThe multi-stage filter, better effect.The phase adjustablePotentiometer from left to right: frequency adjustment, volume controlThe cut-off frequency: 22HZ-240HZPotentiometer shaft center to center spacing: 3cmOP AMP:TL072size: 6.2 x 2.6cmMaterial:ABScolour:As shownPackage Contents:2 x Low Pass FilterOnly 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.