I have made a sallen key low pass filter for my Subwoofer amplifier.I can still hear the voice a little bit.I need without voice.How to cancel the remaining voice in below circuit?
You cannot completely remove all voice frequencies using a simple lowpass filter. The fundamental oscillation frequency of adult vocal chords can be 125 Hz or lower, and the energy in the 2nd and 3rd harmonics is significant. I think that by the time you have a filter than can "completely" remove these frequencies, there will be little left for the sub-woofer to reproduce.
You cannot completely remove all voice frequencies using a simple lowpass filter. The fundamental oscillation frequency of adult vocal chords can be 125 Hz or lower, and the energy in the 2nd and 3rd harmonics is significant. I think that by the time you have a filter than can "completely" remove these frequencies, there will be little left for the sub-woofer to reproduce.
Also remember that a SUBwoofer is supposed to be for frequencies below what a normal "woofer" in a speaker cabinet is capable of - it should really start to have noticeable effect at somewhere below 100Hz, possibly below 60Hz even with decent main speakers.
You might try a 3-pole filter (here) which requires just an added resistor and capacitor at the input, which will give an added 6dB/octave rolloff.
You should adjust the corner frequency to be about 80Hz.