Why a Center Channel Speaker is Needed in Surround Sound

Examples of Center Channel Speakers
Examples of Center Channel Speakers. Images provided by Axiom, Polk Audio, Klipsch, Martin Logan
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There was a time when only two speakers were needed to produce a satisfying listening experience for music. That, of course, can still be the case if you're only listening to music. Many of us, however, use our speakers for more than music. 

Despite a renewed interest in vinyl records, dedicated CD listening, and a new breed of two channel stereo receivers, today's main emphasis on home theater requires new audio formats, receivers, and more speakers to produce the movie theater sound experience at home.

One of the key changes from stereo to home theater is the need for a dedicated center channel speaker.

Center Channel And Stereo

Stereo audio was originally designed as a format that separates recorded sound into two separate channels (that is what the term "stereo" means), with left and right channel speakers placed in front of the room. Although some sounds come specifically from the left and right channel speakers, which creates the stereo sound-stage, principle vocals or dialog are produced by mixing those sounds into both the left and right channel speakers.

Since the vocals are placed in both the left and right channels, when the listener sits in the stereo "sweet spot", which is equidistant between the left and right channel speakers, the vocals appear to come from a phantom center spot between those two speakers.

However, as you physically move your listening position from the sweet spot to either the left or right - even though the dedicated left and right sounds stay in their relative positions, the position of the vocals will (or should) move with you.

You can also hear this effect by using the stereo receiver or amplifier's balance control–as you dial it to the left and right, you can hear the vocals change position with the left and right channel volume output.

To sum it up, in a stereo setup, there is no separate dedicated center channel. As a result, there is no way to control the position or level (volume) of the center channel vocals independently from the left and right channels.

Center Channel And Surround Sound

Unlike stereo, in a true surround sound setup, there is a minimum of 5.1 channels. The speakers a 5.1 channel system are allocated as follows: front L/R, surround L/R, subwoofer (.1), and a dedicated center channel. In surround sound encoding formats, such as Dolby and DTS, specific sounds are mixed into each of those channels - including sounds specifically directed to a center channel. This encoding is provided on DVDs, Blu-ray/Ultra HD Blu-ray Discs, and some streaming and broadcast content.

As of result of how sounds are mixed for a surround sound setup, instead of having the vocals/dialog, placed in a phantom center spot as a result of the same sound coming from both the left and right front channels, the main dialog and vocals are placed in the center channel. Due to this placement, the center channel requires its own speaker. In addition, speakers are also required for the surround L/R, and subwoofer channels.

Although the added center speaker results in a little more clutter, there are distinct advantages to this approach.

  • Since the center channel is separated from the left and right front channels, its volume level can be changed without changing the volume levels of the left and right front channels. This comes in real handy when compensating for dialog/vocals that are too low or too high in a music or movie soundtrack, as you can adjust the volume coming out of the center channel speaker independent of the sounds coming from the rest of the speakers.
  • Sitting in the surround sound sweet spot is desirable, but as you move your listening position from left to right, the vocals/dialog will still appear to come from its center position (although at an angle off-center from the sweet spot) as it would sound like in the real world if a person was talking or singing in that position while you move around the room.

What if You Are Missing a Center Channel Speaker in a Surround Sound Setup?

If you don't have (or don't want to to have) a center channel speaker in a surround sound setup, it's possible to "tell" your home theater receiver via its setup options, that you do not have a center channel speaker.

However, if you use that option, what happens is that receiver "folds" what would be the center channel sound into the left and right front main speakers, just as would in a stereo setup. As a result, the center channel then loses its dedicated center anchor spot and succumbs to the same limitations described in the above roles for vocals/dialog for stereo setups. You wouldn't be able to adjust the center channel volume level independent of the left and right front channel channels.

What a Center Channel Speaker Looks Like

You can use any speaker (except a subwoofer) for your center channel, but ideally you'd use a speaker that has a horizontal, rather than vertical, or square, cabinet design.

The reason for this is not so much technical, but aesthetic. A horizontally-designed center channel speaker can be more easily placed above or below a TV or video projection screen.

What Else to Look For in a Center Channel Speaker

If you are adding a center channel speaker to an already existing speaker setup, try to go with the same brand, and similar mid-range and high-end frequency response capability, as your main left and right speakers.

The reason for this is that the entire left, center, right channel sound-field should sound the same to your ears—this is referred to as "timbre-matching".

If you find yourself unable to obtain a center channel speaker that has similar characteristics of your left and right front channel speakers, if your home theater receiver has an automatic speaker setup system, it may be able to compensate using its equalization capabilities.

Of course, another option, especially if you are putting together a basic home theater setup from scratch, is to buy a speaker system that includes the entire speaker mix—front left/right, surround left/right, subwoofer, and, of course, the center channel.

The Bottom Line

If you are planning a home theater setup, whether you use a center channel speaker is up to you, but here are some things to consider:

  • A center channel speaker provides a specific anchor location for dialog and vocals.
  • The volume level of a center channel speaker can be adjusted independently of the other speakers in a system, providing more flexibility in balancing the total sound of the system.
  • When shopping for a center channel speaker, consider one that has similar sonic characteristics to that of your left and right front main speakers.
  • To facilitate optimal center channel placement, consider one that has a horizontal design so that it can be placed above or below a TV or projection screen and ideally positioned at an equal distance between the front left and right channel speakers.