Subwoofers are definitely an important component in a home theater system, providing the knock-your-socks-off low frequency effects (LFE) impact for all those action and sci-fi movies, as well as the low frequencies from acoustic and electric bass, and even kettle drums, from those jazz, rock, and symphonic albums.
However, just because you have included a subwoofer in your home theater setup, that doesn't mean you are getting all the impact you need, or want. If you have a large room, a room that has acoustical problems, or an irregularly shaped room, you may find that you need more than one subwoofer. For more on the reason why using more that one subwoofer might be beneficial, also read: Using Multiple Subwoofers (About.com Stereos).
Hooking Up More Than One Subwoofer
If you find that you need, or want, more than one subwoofer, the question becomes: "How do I hook-up two, or more, subwoofers in my home theater system?"
The first tip for integrating more than one subwoofer into a home theater setup is that if you are going to use multiple subwoofers in your listening area, it is best to use all of the same brand and model, so as to have the same low frequency reproduction profile for your room.
However, with some added attention, you can combine two different size subwoofers, such as a larger 12-inch sub with a smaller 10 or 8-inch sub, or subwoofers of different brands and models. However, you have to be aware of any differences in power output. For more details on getting the best performance from any subwoofer, check out some useful subwoofer installation tips from About.com Stereos.
Now, before you buy your subwoofers (or combine ones that you already have), make sure they provide the connections that can fit within the three possible setup options below. Also,
The Two Subwoofer Solution
Here are the three ways to add two subwoofers in a home theater system:
1. If your home theater receiver only has one Subwoofer pre-out (sometimes labeled Sub Out or LFE out), just use an RCA Y-Adapter and use it to send two parallel signals to two separate subwoofers.
2. If your home theater receiver has two subwoofer pre-outs, connect one output to one subwoofer and the second one to another subwoofer.
3. If one of your subwoofers has both a RCA Line-in and Line out connection option, connect your home theater receiver's Subwoofer Pre-out the your subwoofer's line in, and then connect the subwoofer's line out to the line-in of a second subwoofer.
Connecting Three or Four Subwoofers
Also, if you are using three or four subwoofers, the best option would be to make sure all your subwoofers have both RCA line and line out connections and just daisy chain them all together using a series of subwoofer cables.
The Wireless Subwoofer Option
However, there is one additional subwoofer connection trick. Both Sunfire and Velodyne make wireless subwoofer adapters that can transmit to up to two or four wireless compatible subwoofers, respectively. In this case, stick with Velodyne or Sunfire wireless subs if possible, but both systems can adapt any subwoofer with RCA line inputs into a wireless sub.
For more on subwoofers, including basics, buying tips, and actual product suggestions read the following supplementary articles: