A subwoofer is essential for deep, dramatic bass. (Velodyne Optimum-8 pictured)

The rumble of an explosion, a crash of thunder, the boom of a drum — some of the most exciting audio effects in home theater are produced by a subwoofer. Subwoofers are individual speaker units that are dedicated solely to reproducing low-frequency sounds, making them a crucial part of your overall listening experience.

Who needs a subwoofer?

The typical frequency range of human hearing is between 20-20,000Hz. A good home theater system should be able to reproduce most of the frequencies within this range. Since front and center channel speakers tend to have trouble reproducing the lowest frequencies, a subwoofer is necessary for filling in the very lowest end of this frequency range.

Bear in mind that low-frequency sound waves are very long, requiring large drivers and a lot of power to reproduce them faithfully. By assigning this difficult job to a dedicated unit (the subwoofer), you'll enjoy those heart-pounding thumps and deep, rumbling roars that make Hollywood blockbusters so thrilling.

If you enjoy listening to music in a two-speaker (stereo) setup, then large floor-standing speakers can deliver good bass response. Still, if you're also using them in a home theater, plan on including a powered subwoofer for an added dose of deep bass. Also, keep in mind that bookshelf speakers have a more difficult time reproducing lower frequencies and, in general, provide less bass response. For these speakers, the extra punch of a subwoofer is crucial.

What to consider when looking for a sub

There are a wide variety of subs out there. To help you pick one, keep these things in mind as you shop:

One of the first things to consider when shopping for a subwoofer is how much power you need. If you have a large room (or if you just crave serious, room-shaking bass) then you should look for a sub with a more powerful built-in amp. Plus, as a general rule, the larger the driver, the deeper the bass — so go for a sub with a big 10" or 12" woofer cone (or a multi-woofer sub) for serious bass response.

Most subwoofers feature a single woofer cone that moves back and forth to create low-frequency sound waves. The woofer cone is usually mounted either on the bottom of the subwoofer cabinet (down-firing) or on one of the sides (front-firing). Neither method is intrinsically better — it all depends on the sub's specific design and on your own personal preferences.

Low-frequency sound waves are omnidirectional, so you have a great deal of flexibility when it comes to subwoofer placement. If you have a spot in your room picked out, consider the dimensions of the sub's cabinet to make sure it will fit. And if you are planning to place your subwoofer anywhere near your TV, be certain to get a video-shielded sub. For more tips, check out our article or our video on speaker placement for home theater.

An in-wall subwoofer uses the space behind your wall or ceiling as a giant cabinet. It can produce deep, powerful bass without taking up any floor space. (Artison RCC-600-SM pictured)

"Enclosure" is another word for the cabinet that houses a speaker. The design of the enclosure can change the performance and output of a subwoofer. Two of the most common types are bass reflex and acoustic suspension.

Acoustic suspension subwoofers use a sealed box to provide bass response. This method reproduces tight, accurate bass, but typically requires more power than a bass reflex design.

Bass reflex enclosures add a "tuned" port to increase and extend the bass response. The port is basically a hole in the cabinet that releases some of the energy created by the inward movement of the woofer cone. Bass reflex subs are more power-efficient than acoustic suspension models, but they sacrifice some accuracy in exchange for the added punch.

All subwoofers perform the same basic function — they reproduce the lowest frequencies in a home theater setup. But some subs also include features that boost performance or make them easier to use.

• No room for a sub? No problem — compact or ultra-compact subs are designed to deliver great bass while being as unobtrusive as possible. Some subs are even designed to be placed on or inside your living room furniture, and some furniture pieces actually come with subwoofers built into them.

Many ultra-compact subwoofers take up less than a square foot of floor space, making them small enough to hide under an end table or in a corner. (Velodyne MicroVee pictured)

• Want the best bass with everything? Check out subs with preset modes — they customize the sub's bass response depending on what you're listening to (Movie, Video Game, Rock Music, Jazz Music, Sports, or Night Listening). Many subs also have some form of built-in equalization to help you customize the sub to the acoustics of your particular listening space. Some subs simply allow you to indicate your sub's placement (corner, mid-wall, in-cabinet, etc.), while higher-end subs may actually take sound samples using an included microphone and automatically tailor the sound to suit your room.
• Don't feel like messing with hard-to-reach controls? To help you manage all your sub's features, look for one that includes a wireless remote control. You'll really appreciate the convenience of not having to get up to adjust the subwoofer's volume knob on the back of the sub every evening when your spouse or children go to bed.

Once you've chosen your sub, check out our tips for getting your subwoofer connected to the rest of your system and on fine-tuning your bass.