Surround Systems: 5.1 vs. 7.1

Given the rise of high-definition movies and television, an audio system capable of delivering sound that matches the quality of the image is essential. A home theater system with surround sound is the ideal setup because it creates sound that allows viewers to feel as if the action is happening around them. Though home cinema systems come in a variety of configurations, two of the most popular remain 5.1-channel and 7.1-channel systems. This buying guide will delve into surround sound technology, the differences between 5.1-channel and 7.1-channel home cinema systems.

Components of a Home Cinema System

All home cinema systems are comprised of a few key components. These include a television or projector, anywhere between two and eleven speakers, a sub-woofer, and a receiver. The receiver is the most critical component of a home cinema system, as it determines what kind of sounds the system can produce. A receiver serves several functions, with its primary purpose being to take the audio signals from input sources like cable boxes, DVD players and Blu-ray players, and video game consoles like the Sony PlayStation 3, Microsoft Xbox 360, or Nintendo Wii, and then amplify the signals and feed them to the speakers. In addition, the receiver serves as the primary control device for the sound settings. It also contains a radio tuner, and some models may have an integrated DVD or Blu – ray player.

How Surround Sound Technology Works

Surround sound technology works by dividing sound into separate channels, which are then fed to individual speakers. As a result, sound is fed to the viewer or listener from all directions.. Surround sound systems are named for the number of channels they use, with a “.1” or “.2” to indicate how many subwoofers are included in the system. However, surround sound technology uses two kinds of channels, discrete or matrix, to produce that sound. A discrete channel is, as the name suggests, one that is completely independent. The sound information encoded for it is available separately from other channels. By contrast, a matrix channel is one in which the sound information is derived from other channels. Surround sound that uses discrete channels is more precise, but matrix channels can produce the same deep sensation.

Surround Sound Formats

When creating surround sound for a television program, movie, or video game, the information is encoded in one or even several formats, which are decoded by the receiver. These formats are typically created by one of two companies: Dolby or Digital Theater Systems (commonly called DTS), though other options exist as well. These formats use a combination of discrete and matrix channels to produce sound, and some are more common than others. Consumers will also want to note that most surround sound formats use some sort of compression to store and transmit the information, which distorts the sound from its original format. Traditionally, DTS uses less compression, but some surround sound formats on Blu-ray discs are said to be “loss-less,” meaning there is no compression at all.

About 5.1-Channel Home Cinema Systems

A 5.1- channel surround sound system uses five speakers and a sub-woofer. These speakers consist of a center-channel speaker placed at the front of the room, centered with the television or projector screen to deliver the majority of dialogue; a front left speaker and a front right speaker, which deliver the majority of the sound effects; and rear left and right speakers, sometimes called surrounds, which cover the remainder of the sound effects.

5.1-Channel Sound Formats

When 5.1-channel surround sound emerged in the late 1970s, the standard format quickly became Dolby Digital. This format is still widely found on DVDs and HDTV broadcasts. However, 5.1-channel receivers may support other formats, as outlined in the chart below.

Format

Channel Arrangement

Used By

Dolby Digital

Five discrete channels and one sub-woofer

DVDs, some HDTV, some satellite and cable TV, some video games

Dolby Pro Logic II

Two discrete channels, three matrix channels, and one sub-woofer

VHS tapes, stereo music, some video games

DTS

Five discrete channels and one sub-woofer

Some DVDs and CDs

 

As seen from the chart, DTS and Dolby Digital both use fully discrete channels and can be found on DVDs and digital media. The Pro Logic II format, by contrast, uses a combination of discrete and matrix channels.

Advantages and Disadvantages of 5.1-Channel Home Theater Systems

A 5.1-channel home cinema system is compatible with all DVDs because all DVDs support Dolby Digital, which has become the standard format. Audiophiles may prefer this type of system because high-resolution music formats like Super Audio CDs and DVD-Audio use 5.1-channel configurations exclusively. For consumers who have made the switch to HD, HDTV broadcasts and Blu-ray discs also support 5.1-channel surround sound. However, many discs also now offer a native 7.1-channel format, which provides high definition audio to complement the high definition graphics, so consumers with a large Blu-ray library may be better served with a 7.1-channel system. On a final note, a 5.1-channel system uses fewer components, so it may be easier to install in smaller rooms.

About 7.1-Channel Home Cinema Systems

A 7.1- channel home cinema system builds on the configuration of a 5.1-channel system, adding two rear center speakers. Certain surround sound formats also allow these two additional speakers to be placed at the front of the room instead, above the television and center-channel speaker to function as front-height speakers. These extra speakers contribute to the background noise as well as directional effects in surround sound.

7.1-channel Surround Sound Formats

As mentioned before, 7.1-channel surround sound was developed to complement high-definition Blu-ray technology. In addition to the array of Dolby and DTS formats. Consumers can opt for receivers that support Audyssey DSX, a processing technology that can upscale 5.1-channel surround sound to 7.1-channel sound and beyond. For native 7.1-channel formats, DSX allows consumers to pick between using two rear center-channel speakers and two front-height speakers.

Format

Channel Arrangement

Dolby Pro Logic IIx

Two discrete channels and five matrix channels, plus one sub-woofer

Dolby Pro Logic IIz

Up to seven discrete channels and a sub-woofer; alternatively, two discrete channels, five discrete channels, and a sub-woofer for some sources

Dolby Digital Plus

Seven discrete channels and a sub-woofer

Dolby True HD

Seven discrete channels and a sub-woofer

DTS-HD

Seven discrete channels and a sub-woofer

DTS-HD Master

Seven discrete channels and a sub-woofer

Advantages and Disadvantages of 7.1-Channel Home Cinema Systems

A 7.1-channel home cinema receiver will provide more depth of sound when the source supports a 7.1-channel format natively, making it ideal for consumers who want HD content frequently. In addition, many 7.1-channel receivers can switch to a 5.1-channel mode and simply relay the same two channels of information to the rear surround and rear center speakers. In addition, some devices can scale the 5.1-channel formats to 7.1 channels. However, consumers will need to ensure they have the space for the extra two speakers in the setup.

Conclusion

Home cinema systems vary drastically in their capabilities and the number of components, but 5.1-channel and 7.1-channel formats remain the most common, as these are the native formats for most content. The difference between the two comes down to the resolution of the video source; while 5.1-channel systems are the default for DVDs, some HDTV, and high-resolution music, 7.1-channel systems are meant for use with HD sources, such as Blu-ray discs. When choosing which system to install in their homes, consumers should look at both the size of the room and their media libraries. A 5.1-channel system is ideal for a smaller space and it is widely supported by DVDs and Blu-ray discs, so buyers do not have to worry about compatibility. However, if the consumer has a larger space in mind for the installation or has a large collection of HD movies, a 7.1-channel system may be the better choice, as most receivers can support 5.1-channel formats. Whichever system buyers opt for, though, eBay is an excellent way to shop.

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