Subwoofer Controller Frequency, Phase, Gain

To create a 2.1 audio system, 5.1 channel home audio or active subwoofer, low pass filter/ Subwoofer controller is required to pass the low frequency and eliminate the high frequency. Because of the low frequencies that spread in all directions, the music recordings are mono low frequency, namely the right and left it's same. So it takes only one subwoofer, this low pass filter circuit should