Before You Buy a Subwoofer - What Factors Are Important?

The ultimate subwoofer buying guide

Subwoofers are a special type of speaker capable of reproducing the lowest of audible frequencies. The ideal subwoofer for your system depends on the characteristics of the room and your own preferences. Here's how to choose a subwoofer that best fits your surround sound setup.

Are Subwoofers Worth It?

Subwoofers are crucial to the home theater experience. When you go to a movie theater, you can often “feel” the sound emanating around you. Subwoofers are responsible for the deep bass that shakes you and hits you right in the gut. To get this experience at home, home theater receivers provide outputs referred to as a Sub out, Sub Pre-Out, or LFE (Low-Frequency Effects).

The best home subwoofers cost hundreds of dollars, but you can find budget subwoofers for under $100. If you have a large home theater, then you'll probably need a higher-end system. For smaller rooms, you'll want a self-powered subwoofer that doesn't require a separate amp.

Polk Audio HTS Subwoofers
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If possible, carry a CD that has a lot of bass information with you when you go to the retailer. That way, you can test out how the bass sounds through various subwoofers before you buy.

Powered Subwoofers

The most common type of subwoofer is one that is self-powered, which means that it has a built-in amplifier. Powered subwoofers usually provide their own volume (gain) and other controls that can be adjusted separately from the home theater receiver.

All a powered subwoofer needs (in addition to AC power) is a connection to the Sub output from a receiver (you don't have to put an extra amp between the subwoofer and the receiver). This connection setup takes the audio power load away from the amp/receiver and allows the amp/receiver to power the midrange and tweeters more easily.

Passive Subwoofers

Passive subwoofers are powered by an external amplifier, in the same fashion as other speakers in your system. To use a passive subwoofer in a home theater setup, the best solution is to place an external subwoofer amplifier between the passive subwoofer and your home theater receiver's subwoofer preamp outputs. This will free the receiver from having to supply the needed amplifier power for the subwoofer.

Low-frequency bass output needs more power to reproduce low-frequency sounds. If you opt to connect a passive subwoofer directly to speaker terminals on the receiver instead of putting a separate amplifier between the sub and receiver, the receiver will need to be able to output enough power to sustain bass effects in the subwoofer without draining the amp. How much power depends on the requirements of the passive subwoofer, the size of the room, and how much bass you desire.

Front-Firing and Down-Firing Subwoofers

Front-firing (or side-firing) subwoofers are designed so that the sound radiates from the side or front of the subwoofer enclosure. Down-firing subwoofers are designed so that the sound radiates downward, towards the floor.

Both types can deliver similar results. Since the deep-bass frequencies reproduced by subwoofers are non-directional, it is very difficult for our ears to actually pinpoint the direction the sound is coming from. Nonetheless, front-firing subs are usually placed in the front of the room, and down-firing subs deliver the best results when placed in a corner or sidewall.

When handling a down-firing subwoofer, be careful not to puncture the exposed driver when you pick it up or set it down.

Ports and Passive Radiators

Some subwoofer enclosures also have an additional port that forces out more air, increasing bass response in a more efficient manner than sealed enclosures. Other enclosures utilize a passive radiator in addition to the speaker, instead of a port, to increase efficiency and preciseness.

A passive radiator can be a speaker with the voice coil removed or a flat diaphragm. Instead of vibrating directly from the electrically transmitted audio signal, a passive radiator reacts to the air that is pushed by the active subwoofer driver. Since the passive radiator complements the action of the active driver, it helps to increase the low-frequency response of the subwoofer.

Subwoofer Crossovers

The crossover is an electronic circuit that routes all frequencies below a specific decibel point to the subwoofer. All frequencies above that point are routed to the main, center, and surround speakers. Typically, a good subwoofer has a crossover frequency of about 100hz.

Subwoofer Placement

Since the low frequencies reproduced by a subwoofer are non-directional, it can be placed anywhere in the room where it sounds best. Optimal placement depends on room size, floor type, furnishings, and wall construction. Typically, the best placement for a subwoofer is in the front of the room, just to the left or right of the main speakers, or in a front corner of the room.

Many home theater receivers provide two subwoofer outputs, making it possible to connect two or more subwoofers.

Wired or Wireless?

A growing number of powered subwoofers offer wireless connectivity. The wireless capability eliminates the need for a long connection cable between the subwoofer and the receiver. A wireless-enabled subwoofer usually comes with a transmitter kit that can be plugged into the subwoofer outputs of any home theater receiver.

The transmitter connected to the home theater receiver transmits low-frequency audio signals to the wireless subwoofer. In turn, the wireless receiver built into the subwoofer allows the built-in amplifier to power the speaker driver, producing the needed low-frequency sound.