Audio

Speakers Intro

Speaker Channels: Home Theater
Stereo, Center, Surround and Subwoofer

There are four primary types of audio channels speakers operate in: 

1) Stereo main front - left and right channels, 
2) The center channel, 
3) Surround sound (or rear channel) - left and right channels, special effects,
4) Low frequency effects channel (subwoofer channel) LFE in 5.1 audio systems.

The four types of channels equate to up to six individual channels. Of these, the two front stereo channels are the basis for all audio systems.

Stereo systems are comprised of two audio channels, left and right. These two channels require full-range speakers and are used to reproduce stereo program material. Floor-standing and bookshelf speakers may be used as main stereo speakers, and there is no limit to the variety of technologies and techniques used in these types of loudspeakers.

The main left and right stereo channels are called upon to reproduce sounds across the entire audible frequency spectrum except when a subwoofer is used. The subwoofer may then often take over the low bass ranges below 80 Hz. The main stereo channels may use dipolar, bipolar, omni-directional or direct radiating sound reproduction techniques.

In a home theater system, the main left and right speakers are placed on either side of the television video display or video screen. They provide the bass frequencies if a subwoofer is not in use.

Placed between the front left and right stereo speakers in a multi-channel audio system is the center channel speaker. The center channel is located equidistant from the other two front speakers in a straight line with them. This speaker is often placed on top of or below a television. It may also be placed below a projection screen, or center channel speakers may be placed behind acoustically transparent screens. Such video screens feature hundreds of tiny holes per square inch that allow sound waves to travel through the screen without signal degradation (although there may be a slight high frequency roll-off).

Center channel speakers are typically long and short arrayed in a horizontal direction atop a television. They must be magnetically shielded to be placed on or near a cathode ray tube video display. They also tend to be reasonably small bookshelf style speakers lacking in bass output.

The center channel is used to anchor voices and other on-screen action to the screen in a movie. Center channel speakers must be carefully matched to their stereo pair partners so that the sound of the three speakers remains the same or very similar. They also are called upon to reproduce up to 50 or 60 percent of a movie soundtrack. For these reasons, center channel speakers should be of the same quality as the other front channel speakers, and they should be powered with the same amount of power and quality of amplifier.

Rounding out the multi-channel home theater speaker array are the surround channels. The left and right surround or rear speakers provide ambience and depth to a soundtrack. As such, these speakers tend to play a less critical role compared to their cousins across the front of the room. However, rear speakers should be matched in quality and amplifier power to the front channels whenever possible. Discrete digital surround sound formats such as DTS and Dolby Digital have made full-range, stereo surround speakers a necessary element of the home theater. As such, the surround channels are taking a more important role in the overall acoustic scheme or things and will continue to do so into the future.

Most surround speakers tend to be bookshelf type designs. They are most often placed to the sides of the listener or behind the listener and are mounted up on the wall six feet or higher. They do not generally offer bass into the lowest octave or two, but those ranges are picked up by the main stereo speakers or the subwoofer.

In their position as primarily ambience creators, surround speakers often benefit form a diffuse, spread-out sound. To achieve this, many dedicated surround speakers operate in a bipolar or dipolar fashion. In fact, all THX certified surround speakers must be dipolar due to their broad sound field and their ability to be difficult to localize.

Providing the punch and foundation in a home theater system and many dedicated stereo systems is the subwoofer. The subwoofer reproduces only low bass frequencies from around 80 Hz down to 20 Hz or below. Subwoofers produce massive sound waves that can be felt as much as they can be heard. They generate the deepest bass that most other speakers have difficulty producing, if they can produce those frequencies at all.

Digital surround sound formats (5.1 formats) feature a dedicated low frequency effects channel designed specifically for a subwoofer or subwoofers. While a sub is not necessary if the other speakers in an audio system can produce full range sound down into the bottom octave, it provides an extra degree of visceral impact that is rarely achieved with traditional speakers, even large floor-standing models.

Subwoofers require system matching in order to operate to their maximum potential in a given audio system, but they are much less prone to tonal difficulties and inconsistencies creating discernible problems compared to matching center speakers and surround speakers with stereo models. Additionally, subwoofers may be placed anywhere in a room thanks to the fact that frequencies below about 80 Hz are not localizable. This means that a subwoofer does not need to be placed near the front speakers and a single subwoofer can reproduce the bass for an entire array of speakers without sonic degradation or damage to a system's imaging or sonic appeal. In fact, the versatility of subwoofers allows them to be placed optimally for superior bass output while the other speakers in a system can be placed without regard to low bass performance increasing the chances of providing a realistic, satisfying audio experience.

While center, surround and stereo speakers typically feature an array of drivers or other sound producing transducers that are powered by external amplifiers, most subwoofers feature one or two large drivers powered by their own internal amplifier (active speakers). Additionally, most subwoofers are dynamic in design and typically direct radiating. Subwoofer drivers tend to measure 12 to 18 inches in diameter and most subwoofer amplifiers feature at least 100 watts of power while many exceed 200 watts or more.

Combined as a complete system, the stereo speakers, center channel speaker, surround speakers, and subwoofer create a convincing, complete home theater system. A well designed home theater using quality speakers and associated electronics often surpasses the quality of sound found in most commercial movie theaters complete with booming bass and sounds that fly around the room. As an individual pair, main stereo left and right speakers provide a traditional audio reproduction path for CDs, radio, tapes, and more.

Loudspeakers:

Speaker concepts
Crossover networks
Speaker fundamentals
Inside speakers
Speakers and sound
Speaker terms
Loudspeakers Buying Guide
Speaker channels
Speaker wire connections
Subwoofers