Subwoofers - What You Need To Know

Subwoofers, bass shakers, and tactile transducers enhance your system

Klipsch Reference Subwoofers
Klipsch Reference Subwoofers. Image provided by Klipsch Group

When you go to the movies, you are not only impressed with the large and colorful images on the screen, but the sound emanating all around you. What really makes the experience, though, is the deep bass that shakes you up and punches you right in the gut. That deep bass is produced by a subwoofer.

What a Subwoofer Is

A subwoofer is a type of speaker that reproduces only the lowest of audible frequencies. In home theater, this feature's called low-frequency effects.

Home theater surround sound is implemented by 5 or more channels, with each channel represented by a speaker. The surround sound channel dedicated to the subwoofer is referred to as the .1 channel.

With home theater sound systems requiring specialized speakers for center channel dialog, main soundtracks, surround, and sometimes even height effects, the need for a speaker to reproduce just the deep bass portion of a movie soundtrack is all the more important. Although a home subwoofer is not quite as "thunderous" as the ones at the local movie theater, it can still shake the house or annoy the downstairs neighbors in your apartment or condo complex.

Types of Subwoofers

  • Passive: This type of subwoofer is powered by an external amplifier, in the same way as the other speakers in your system. Extreme bass needs more power to reproduce low-frequency sounds, so an amplifier or receiver must output enough power to sustain bass effects through the subwoofer without draining the amp. The amount of power depends on the requirements of the speaker and the size of the room.
  • Powered: Powered subwoofers combine the subwoofer speaker and an amplifier inside the same cabinet. All a powered subwoofer needs, in addition to AC power, is a line output (sub out, pre-out, or LFE out) from a home theater receiver. This arrangement takes a lot of the power load away from the amp/receiver and allows the amp/receiver to power the mid-range and tweeters more easily. Most subwoofers used in home theater setups are the powered type.

Additional Subwoofer Characteristics

Various additional design variations and setting options employed in subwoofers further optimize low-frequency performance.

  • Front-firing subwoofers employ a speaker mounted so that it radiates the sound from the side or front of the subwoofer enclosure.
  • Down-firing subwoofers employ a speaker that radiates downward, toward the floor.
  • Ports: In addition to the speaker portion of the subwoofer, some enclosures offer an additional port, which forces out more air, increasing bass response in a more efficient manner than sealed enclosures. This type of ported design is referred to as bass reflex.
  • Passive Radiator: Some subwoofers use a passive radiator in addition to the speaker, instead of a port, to increase efficiency and preciseness. Passive radiators can either be speakers with the voice coil removed or a flat diaphragm.
  • Crossovers: The crossover is an electronic circuit that routes all frequencies below a specific point to the subwoofer; all frequencies above that point are reproduced the main, center, and surround speakers. A typical crossover point would be between 80Hz and 100Hz.
  • Directionality: Deep-bass frequencies reproduced by a subwoofer are non-directional. It is difficult for human ears to pinpoint the direction of sound. That is why we can only sense that an earthquake seems to be all around us, rather from coming from a particular direction. Due to the non-directional characteristics of extreme low-frequency sound, a subwoofer can be placed anywhere in the room where it sounds best in relation to room size, floor type, furnishings, and wall construction.

Subwoofer Installation Tips

Typically a subwoofer is placed in the front of a room, near the front left or right main speaker. However, they can also be placed on a side wall or in back of the room. Where it sounds best will determine the final placement.

The subwoofer should not sound "boomy," but deep and tight. This attribute is especially important if you intend to use your subwoofer for music. Many subwoofers are great for Blu-ray Disc or DVD movies, but may not perform well with the subtle deep bass in music performances.

When installing your subwoofer, experiment with the crossover settings. In addition to the settings available on the subwoofer, most home theater or AV receivers use crossover (also referred to as bass management) settings for your subwoofer as well. Using either crossover setting option, a subwoofer can either take the entire bass load or split the bass load with large main speakers.

Also, if you live in an upstairs apartment, a down-firing subwoofer may disturb your downstairs neighbors more readily than a front-firing design. In some cases, integrating two subwoofers into your system may provide a better option, especially in a very large room.

Beyond The Subwoofer

ButtKicker Advance
ButtKicker Advance. Image via ButtKicker

If you really want to pump things up consider, the following upgrades to your home theater and subwoofer setup.

The Buttkicker: The buttkicker is not a conventional subwoofer. Using a suspended magnetic system to reproduce sound waves that are not air dependent, the buttkicker can reproduce frequencies down to 5HZ. This is well below human hearing, but not below human feeling. Variations of the Buttkicker are found in some movie theaters, and concert halls, but has been adapted for use in a home theater environment.

Clark Synthesis Tactile Sound Transducer: With a very compact transducer design, the Clark Synthesis Tactile Sound Transducer can be placed inside (or on the bottom of) chairs, couches, etc. to produce a deep bass response that is both intimate and effective.

Bass Shakers: Bass shakers reproduce inaudible low frequencies, designed to give an extra punch to your sound system. The shaker is usually attached directly to the object to be shaken, such as a chair (similar to the Clark Tactile Transducer) in order to realize its effect. Bass shakers work by themselves or in conjunction with a regular subwoofer setup.

Tactile Transducer/Bass Shaker Installation

Each brand or model of tactile transducer or bass shaker has specific installation requirements that are provided by the manufacturer, but in general terms, these devices are usually placed between the floor and a chair, couch, or furniture legs, or attached directly to them, and, in some cases, you can purchase home theater seating with such devices already built-in. Also, since these devices work below the range of human hearing, they should be used in conjunction with a conventional subwoofer, not in place of it.

Although transducers and shakers are effective for effects that contain a lot of inaudible low-frequency information—such as explosions, earthquakes, gun blasts, rocket, and jet motor effects—they are not effective in the typical home music listening environment. A good subwoofer is more than adequate for the lowest musical effects, such as acoustic bass and bass drums.