What Does the .1 Mean in Surround Sound?

Surround Sound and .1

Image of Jamo J 112 Sub Subwoofer. Image provided by the Klipsch Group, Inc.

One of the concepts in home theater that can be confusing for consumers is what the terms 5.1, 6.1, and 7.1 mean with regards to surround sound, home theater receiver specifications, and DVD/Blu-ray Disc movie soundtrack descriptions.

It Is All About The Subwoofer

When you see a home theater receiver, home theater system, or DVD/Blu-ray disc soundtrack being described with the terms 5.1, 6.1, or 7.1, the first number refers to the number of channels that are present in a soundtrack or the number of channels that a Home Theater Receiver can provide.

These channels reproduce a full range of audio frequencies, from high frequencies to normal bass response. This number is usually stated as 5, 6, or 7, but you may also find on some home theater receivers, it can be as high a 9 or 11.

However, in addition to 5, 6, 7 or more channels, another channel is also present, which only reproduces the extreme low frequencies. This extra channel is referred to as the Low Frequency Effects (LFE) channel.

The LFE channel is designated in home theater receiver or DVD/Blu-ray disc soundtrack specifications with the term .1. This is due to the fact that only a portion of the audio frequency spectrum is reproduced. Although LFE effects are most common in action, adventure, and sci-fi movies, they are also present in many pop, rock, jazz, and classical music recordings.

In addition, to hear the LFE channel, the use of specialized speaker is required, called a Subwoofer.

A Subwoofer is designed only to reproduce extreme low frequencies, and cuts-off all other frequencies above a certain point, usually in the range of  100HZ to 200HZ.

So, next time you see the terms describing a home theater receiver/system or DVD/Blu-ray Disc soundtrack as including 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, you will know what the terms are referring to.

The .2 Exception

Although the .1 designation is the most common designation to represent the LFE channel, you will also run into some home theater receivers that are labeled as having 7.2, 9.2, 10.2, or even 11.2 channels. In these cases, the .2 designation means that these receivers have two subwoofer outputs. You don't have to use both, but it may come in handy if you have a very large room, or are using a subwoofer with lower power output that you desire.

The Dolby Atmos Factor

To complicate things a little more, if you have a Dolby Atmos-enabled home theater receiver and surround sound setup, the speaker designations are labeled a little differently. In Dolby Atmos, you will encounter channel/speaker setups that are labeled as 5.1.2, 5.1.4, 7.1.2, or 7.1.4.

In the Dolby Atmos nomenclature, the first number refers to the traditional 5 or 7 channel horizontal speaker layout, the second number is the subwoofer (if you are using 2 subwoofers, the middle number can be a 1 or a 2), and the third number refers to number of vertical, or height, channels, which are represented by either ceiling mounted or vertically firing speakers. For more details, read our article: Dolby Reveals More Details On Dolby Atmos For Home Theater.

Is The .1 Channel Really Required For Surround Sound?

One question that comes up is whether you really need a subwoofer to get the benefits of the .1 channel.

The answer is Yes and No. As discussed in this article, the .1 channel and subwoofer are designed to produce the lowest frequencies present in a soundtrack that is encoded with this information.

However, there are many consumers that have large floor standing left and right main speakers that actually produce pretty good bass via "standard" woofers.

In this type of setup, you can tell your home theater receiver (via its setup menu) that you aren't using a subwoofer and to send low bass frequencies so that the woofers in your left and right speakers perform this task.

However, the issue then becomes whether those woofers in your floor standing speakers really produce low-enough bass, or if they can do so with enough volume output. Another factor is whether your home theater receiver has enough power to produce low frequencies.

If you think that this option will work for you, the best thing to do is to do your own listening text at moderate volume levels. If you are satisfied with the result, that is fine - but if you aren't, you an take advantage that 1. channel subwoofer preamp output on your home theater receiver.

More Info

For a more detailed explanation of Surround Sound and what the terms Dolby Digital, Dolby Digital EX, and DTS mean, check out our additional resource article: The History and Basics of Surround Sound.

In addition, for more information on Subwoofers, check out my resource article: Subwoofers - What You Need To Know