These are the common method to connects your subwoofer in your system. They are three popular methods you can use, passive filter-passive subwoofer, passive filter-active subwoofer, active filter-active subwoofer.
The first method, passive filter-passive subwoofer. We usually used a dual voice coil subwoofer in this system, filters are used to block the low bass from the main speakers and higher frequencies from the subwoofer. There is no control over the output level of the subwoofer relative to the rest of the system because all drivers are driven by the same amplifier. It can also be expensive to build filters that dedicated for the required low frequencies of <120 Hz. Remember passive bandpass subwoofer would need filter also, but one well outside of its bandpass.
The second method, passive filter-active subwoofer. The sub will be driven by its own amp, and you are able to set the sub’s output level to match the rest of the system. But this passive filter are also expensive to build.
The third method, active filter-active subwoofer. The passive filter are replaced by active filter resulting a greater flexibility. This is the perfect method, you can easily fine-tune the system to get the best outcomes. If your amp has a pre-out/main-in jacks, use the sub amp with a line-level x-over with a high-pass line-level output. Then connect your amp’s pre-out jacks to the line-in jacks on the sub amp, now connect the high-pass line-out jacks from the sub amp into the main-in jacks on the amp. This will take care of the filtering requirement for the main speakers.
