Many different components all together make up a good subwoofer. The main sound track is rendered by one speaker, when the dialogue is the main area of concern for the other. The sound effects are contributed by another component and altogether the subwoofer mainly concentrates at rendering prominent bass.
Types of Subwoofers
Any home theatre subwoofer would fall within these two broad criteria:
1. Passive Subwoofer: A passive subwoofer is the one that has an amplifier or an external receiver.
2. Self-Powered Subwoofer: The other one is the self contained powered subwoofer, and just as the name itself suggests, the power is being produced from inside itself.
Comparing Passive & Self-Powered Subwoofers
The passive subwoofer does not produce enough power to render the deeper bass. This is where the second type wins over the first as it has already been built with the required power.
Therefore, the selection of a passive or a self-powered subwoofer will depend upon your intended purpose of usage, and several other factors such as room size.