Speaking the Language of Surround Sound: A Glossary of Terms

Surround Sound Intro

Ready to take the plunge into surround sound, but confused by all those techy terms? Find out what it all means.

Mono vs. Stereo

Mono sound. Mono refers to a setup in which all of the sound you hear comes from a single channel represented by a one speaker.

Stereo sound. Stereo refers to a setup where all the sound you hear comes from two channels, represented by two speakers — one positioned on the front left side of your listening spot, and the other positioned on the front right side of your listening position.

The advantage of stereo over mono is that with stereo sound, sound is placed in a more realistic fashion across a “stage,” similar to instruments in a band or orchestra. However, there is still the limitation in that all of the sound you hear originates from the front of your listening environment, rather than from multiple directions, which is the way humans hear.

From Stereo to Surround Sound

Surround sound. In this type of setup, sound not only comes from the front, but also from channels positioned on the sides, at the rear and sometimes from above.

5.1 channel setup. In addition to the front left and right channels, a basic surround sound setup also features a center channel, two surround channels and a subwoofer. This arrangement is referred to as a 5.1 channel setup.

The left and right channels still retain most of the role they would have in a stereo setup, and most of the sounds you hear will originate from the left and right channels. However, for movies, in order to provide a better anchor and control of dialog, a dedicated center channel and speaker is added. The main role of the surround channels is to fill in the ambience (such as acoustics of a large room) and provide directional sound for moving objects, such as cars, bullets, wind, planes, helicopters, etc. The surround channels are not always active.

The subwoofer. OK, so now we have 5 channels, left front, center, right front, left surround, and right surround, but there is also the .1 channel, which is represented by the subwoofer. The subwoofer is designed to reproduce the extremely low bass frequencies (mostly in movies) that the other speakers are not equipped to handle. Due to the fact that the subwoofer only reproduces a small portion of the frequency range, is it referred to as the .1 channel instead of a full sixth channel.

Also, unlike the rest of the speakers, the subwoofer can be placed anywhere in the room as extremely low bass frequencies are non-directional (in other words, you can’t pinpoint the exact location of the sound). However, depending on the characteristics of the specific room, some spots will result in deeper and clearer bass than other spots. On the other hand, in most surround sound setups, the subwoofer is placed on either the left or right front side of the room between the left or right front speaker and the center channel speaker.

Independent sound control. In a 5.1 channel setup, each speaker can be controlled independently. Most home theater receivers (also referred to as AV or surround sound receivers) provide the user with the ability to set the sound output level of each channel without affecting the sound output level of the other channels. Once this part of the setup process is completed, when you raise or lower the master volume level of the entire system, the sound relationship between each channel is retained, providing the proper sound level balance between all of the channels.

Beyond 5.1

In the world of surround sound, the 5.1 channel concept is just the beginning. There are a lot more options, but the most common upgrade from the 5.1 channel setup is 7.1 channels.

7.1 channel setup. In addition to the front left/right, center and surround left/right speakers, two additional speakers are positioned behind the listening position (usually against the back wall), one on the left and other on the right. These are referred to as the surround back channel speakers.

5.1.2 channel setups. There are two additional 7.1 channel variations which are, oddly enough, referred to as 5.1.2 channel setups. More on that in a bit. In both of these variations, the 5.1 channel speaker setup is the same, and then:

  • First variation – Two height channel speakers are added about 3 feet above the front left and right channel front speakers. These adds depth and create a broader front soundfield.
  • Second variation – Two speakers are added on the ceiling, or two vertically firing speakers are positioned on top of the front left and right channel speakers. This provides a more immersive surround sound experience by adding the capability of locating sounds overhead of the listening position.

When using either of the above options, instead of the 7.1 designation, the arrangement is referred to as a 5.1.2 channel setup, where 5.1 represents the foundation 5.1 channel speaker arrangement, the .1 represents the subwoofer, and the added .2 represents either the ceiling mounted or vertically firing speakers.

On and on it goes. Of course, if you really want to get carried away, there are also 9.1, 10.1 and even 11.1 channel setup options. Also, changing the number of subwoofers changes the channel designation as well, so instead of 5.1 or 7.1, you may encounter setups that have 5.2 or 7.2 channel designations, where the .2 refers to two subwoofers.

However, despite all of the surround sound channel and speaker variations that can be used, the vast majority of home theater setups are of the 5.1 channel variety.