What Does the .1 Mean in Surround Sound?

In discussing home theater systems you often seen 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.

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 there are systems 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 referred to as the Low-Frequency Effects (LFE) channel. LFE is important for movie soundtracks, as they provide deep booming tones, but they are also important for high-fidelity music.

An LFE channel requires the use of a subwoofer. Subwoofers are 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.

Although the .1 designation is the most common designation for the LFE channel, some home theater receivers are labeled as having 7.2, 9.2, 10.2, or even 11.2 channels. This means the receivers have two subwoofer outputs. You do not 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.

Speaker designations are labeled differently for Dolby Atmos-enabled home theater receivers and surround sound systems. They are typically labeled as such: 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. These channels are delivered through ceiling mounted or vertically firing speakers.

No. The .1 channel and subwoofer are designed to produce very low frequencies, but there are plenty of floor-standing stereo (left and right) speakers that 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 the floor standing speakers can produce enough bass to satisfy your ears. Oftentimes they cannot. Some speakers from brands like Definitive Technology produce standing stereo speakers with embedded subwoofers for either .1 or .2 channel setups.

Also, home theater speakers can always be bought piecemeal, meaning you can purchase a stereo pair first, and then get a subwoofer at a later date.

There are several ways to manage the LFE or .1 channel in your home theater system. It may include a separate, dedicated subwoofer; a basic two-speaker setup equipped to produce low frequencies; or a pair of floor-standing speakers with embedded subwoofers. The choice is yours, but without that extra bass you will surely miss out on the full surround sound experience.