One of the concepts that confuses consumers is what the terms 5.1, 6.1, and 7.1 mean with regards to surround sound and home theater receiver specifications.
It Is All About The Subwoofer
In 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 5, 6, or 7 you may also find on some home theater receivers, it can be as high a 9 or 11.
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.
This channel is designated with the term .1, due to the fact that only a portion of the audio frequency spectrum is reproduced. In addition, this LFE channel requires the use of specialized speaker, 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 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
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.
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 my article: Dolby Reveals More Details On Dolby Atmos For Home Theater.
In addition, for more information on Subwoofers, check out my resource article: Subwoofers – What You Need To Know