What Does the .1 Mean in Surround Sound?

In discussing home theater systems, you often see the following terms tossed around: Dolby Digital 5.1, Dolby Digital EX (6.1), Dolby TrueHD 5.1 or 7.1, DTS 5.1, DTS-ES (6.1), DTS-HD Master Audio 5.1 or 7.1, or PCM 5.1 or 7.1. But what do they mean?

Dolby and DTS are brands that license their audio encoding technologies to various electronics manufacturers. The number following the brand name refers to the type of sound system that a device or media is formatted for. These systems include surround sound, home theater receivers, DVD/Blu-ray players and discs, and other components.

What Does 5.1 Channel Mean?

The first number in, for example, "Dolby 5.1," refers to the number of channels that a home theater receiver can provide. It may also refer to the number of channels present in a film, TV, or video soundtrack. It is more common for systems to support 5, 6, or 7 channels, but some systems are available with as many as 9 or 11 channels.

The second number in the specification refers to a separate channel that only reproduces very low frequencies. This extra channel is a Low-Frequency Effects (LFE) channel. LFE is essential for movie soundtracks, as they provide deep booming tones, but they are also crucial for high-fidelity music.

An LFE channel requires the use of a subwoofer which is designed to reproduce only very low frequencies. They typically cut off all frequencies above a certain point—usually those in the range of 100HZ to 200HZ.

The .2 Exception

Although the .1 designation is the most common designation for the LFE channel, some home theater receivers have 7.2, 9.2, 10.2, or even 11.2 channels. The .2 suffix means the receivers have two subwoofer outputs. You don't have to use both, but it can help saturate large rooms with a rich, bass-heavy response. It is also helpful when using a subwoofer with a less than optimal power output.

The Dolby Atmos Factor

Dolby Atmos-enabled home theater receivers and surround sound systems have different designations. They're typically labeled as 5.1.2, 5.1.4, 7.1.2, or 7.1.4.

In the world of Dolby Atmos, the first number refers to the traditional 5 or 7 channel horizontal speaker layout, and the second number refers to the subwoofer. But the third number refers to how many vertical or "height" channels the system has. These channels are delivered through ceiling-mounted or vertically firing speakers.

Is the .1 Channel Required for Surround Sound?

No. The .1 channel and subwoofer produce very low frequencies, but plenty of floor-standing stereo speakers produce a decent bass response. You can usually set up your home theater receiver to send low frequencies to the left and right main speakers instead of a subwoofer.

The question, then, is whether the small subwoofers in floor-standing speakers can produce enough bass to satisfy your ears. Often they can't. Some speakers from brands like Definitive Technology make standing stereo speakers with embedded subwoofers for either .1 or .2 channel setups.

Also, you can purchase a stereo pair first and get a subwoofer at a later date.

The Bottom Line

Manufacturers manage the LFE or .1 channel in a home theater system in various ways. For example, the setup may include a separate, dedicated subwoofer or a basic two-speaker equipped to produce low frequencies. Or, it might consist of a pair of floor-standing speakers with embedded subwoofers. The choice is yours—but without that extra bass, you'll miss out on the full surround-sound experience.