Before You Buy a Subwoofer: What Factors Are Important?

Subwoofers are a special type of speaker capable of reproducing the lowest audible frequencies. The ideal subwoofer for your system depends on the characteristics of the room and your 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 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, use a home theater receiver that provides outputs referred to as a Sub Out, Sub Pre-Out, or LFE (low-frequency effects).

The best home subwoofers cost hundreds of dollars. However, you can find budget subwoofers for under $100. If you have a large home theater, you may need a high-end system. For small rooms, choose a self-powered subwoofer that doesn't require a separate amp.

Powered Subwoofers

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

A powered subwoofer needs a connection to the Sub output from a receiver (you don't need 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.

Passive Subwoofers

An external amplifier powers a passive subwoofer in the same fashion as other speakers in your system. The best solution for using a passive subwoofer in a home theater setup is to place an external subwoofer amplifier between the passive subwoofer and the home theater receiver's subwoofer preamp outputs. This setup frees the receiver from supplying the needed amplifier power for the subwoofer.

Low-frequency bass output needs more power to reproduce low-frequency sounds. Suppose you connect a passive subwoofer to the receiver's speaker terminals instead of a separate amplifier between the sub and receiver. In that case, the receiver must output enough power to sustain bass effects in the subwoofer without draining the amp. The amount of power depends on the passive subwoofer's requirements, 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. In down-firing subwoofers, the sound radiates downward toward the floor.

Both types deliver similar results. Since the deep-bass frequencies reproduced by subwoofers are non-directional, it's difficult for our ears to pinpoint the direction the sound comes from.

Nonetheless, front-firing subs are usually placed in the front of the room. Down-firing subs deliver the best results when placed in a corner or side wall.

Ports and Passive Radiators

Some subwoofer enclosures have an additional port that forces out more air, increasing bass response more efficiently than sealed enclosures. Other enclosures use 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 pushed by the active subwoofer driver. Since the passive radiator complements the action of the active driver, it increases 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 100 Hz.

Subwoofer Placement

Since the low frequencies reproduced by a subwoofer are non-directional, you can place it 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, to the left or right of the main speakers, or in the front corner of the room.

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.