The Subwoofer DIY Page v1.1
How should I connect my subwoofer?
last updated: 09 August 2015
The following are the three usual methods of connecting subwoofers to your system.

Method 1: passive filters, passive subwoofer
A dual-voice-coil (DVC) driver is normally used in this method. Filters are used to block the low bass from the main speakers and higher frequencies from the subwoofer. All drivers are driven by the same amplifier, so there is no control over the output level of the subwoofer relative to the rest of the system. Also, it may be expensive to construct filters that work at the required low frequencies (<120 Hz). Note that a passive bandpass subwoofer usually requires filter as well, but one well outside of its passband.

Method 2: passive filters, active subwoofer
Here the subwoofer is driven by its own amplifier and you can adjust the output level of the subwoofer to match the rest of your system. As before, the passive filters may be expensive to construct.

Method 3: active filters, active subwoofer
Here, the passive filters are now replaced by active filters for even greater flexibility. This is the preferred method, as now you can easily fine-tune the system to achieve the best results. If your amplifier has pre-out/main-in jacks, then use a subwoofer amplifier with a line-level x-over with a high-pass line-level output. You can then connect your amplifier's pre-out jacks to the line-in jacks on the subwoofer amplifier, then connect the high-pass line-out jacks from the subwoofer amplifier into the main-in jacks on the amp.  This will take care of the filtering requirement for your main speakers.

Home Theater: Typically, your home theater receiver will provide all the active filtering that you will need (usually referred to as "bass management" in the receiver's manual). However, it is still a good idea to use a subwoofer amplifier that comes with its own line-level x-over, for the additional flexibility this provides.