You get the very best sound reproduction and performance from passive subwoofers. Power your subwoofer with an external amplifier that has digital signal processing built in so that you deliver only the low frequencies to the subwoofer. An 18” point source subwoofer operates at less than 105 Hz s...o all the frequencies above this go to the mid-high speakers. For the ultimate control of all of your dedicated subwoofer amplifiers use a speaker management processor. Pay close attention to impedance, many professionals suggest that the lowest impedance for a subwoofer should be 4 Ohm.