2.1 To 11.1.8 What Does It All Mean? – A Refresher

Image Credit: Dolby Labs

Thru the years sound reproduction has really ratchet itself up. From the good old days of mono, on to stereo and now the skies the limit for the number of speakers that your want to surround yourself with to get that really immersive feeling….just as if you were there! As speaker configurations became more complicated, with them being placed up-front, to the sides and rear, and now on the ceiling. A common shorthand using three numbers has been developed as a  way of describing the myriad of speaker layouts and channels.

Generally speaking each amplifier channel feeds one speaker so the number of amplifier channels equals the number of speakers. There is a slight deviation from this arrangement for subs, see “b” below.

The format is “a.b.c“, where:

1. “a” is the number of channels or speakers at or near ear level.
2. “b” is the number of channels or speakers dedicated to low bass reproduction. (Be careful with this number as there is only EVER ONE bass channel in a mix. Some reviewers and manufacturers use numbers greater than 1 to indicate the number of subs that the AVR or Processor can support. E.G. 5.2 would indicate that the device can support two subs. Remember that depending upon the level of equalization in the device it may only be a parallel feed rather than an separately equalized and controlled sub channel. 5.3 would indicate three sub outputs.) This fact is VERY important when using multiple subs, see my later comment.
3. “c” is the number of overhead channels or speakers.

The above speaker/channel format applies equally to all sound systems from AV Receivers to discrete speakers and soundbars, home theaters and professional movie studios.

If a system does not have any dedicated height/overhead channels, then the last digit is always left off.  Here are some typical examples:

Some Common Configurations:

• 1.0 – Describes a monophonic sound system with just one speaker reproducing all of the sound
• 2.0 – A standard “stereo system” – it has two speakers to reproduce a stereo sound-field
• 2.1 – A standard stereo system with one dedicated bass channel for low bass reproduction (subwoofer channel)
• 3.0 – Similar to a 2.0 stereo system, but it adds a dedicated center speaker between the front left and right speakers. This can help in reproducing movie dialog and commentary clearly.
• 3.1 – A three channel system with the addition of one dedicated bass speaker channel
• 4.0 – The basic surround system. It uses two speakers in the front and two in the rear or side to reproduce surround sound. A system with three speakers in the front (left, center, right) and one in the rear of the room would also qualify as 4.0
• 4.1 – A four channel system with the addition of one dedicated subwoofer
• 5.0 – The traditional surround sound configuration. It has three speakers across the front (front left, center and front right) and two speakers on the sides or in the rear to generate surround sound
• 5.1 – A five channel surround system with one dedicated subwoofer speaker channel
• 7.0 – An expanded surround sound system having three speakers in the front (left, center right), two on the side (side surround) and two in the rear (rear surround)
• 7.1 – A seven channel surround system with one dedicated subwoofer channel.
• 5.1.2 – This is a “standard” 5.1-channel surround sound system, with the addition of two height channel or speakers that generate sound from above the listener
• 5.1.4 – As above, but with four height channels/speakers to generate sound above the listener
• 7.1.2 – This is a standard 7.1-channel system with two additional speakers dedicated to reproducing sound above the listener
• 7.1.4 – As above, but with four height channels or speakers

See this Dolby speaker setup publication for more details: Dolby Atmos® Home Theater Installation Guidelines.

Image Credit: Dolby

The Dolby Atmos system pictured here includes 12 speakers in a 7.1.4 speaker configuration.

Just How Many Channels is Enough?

Few Home Theaters systems support more than 11.1.8, nor are there many AV receivers or processors that can drive that many speakers, with 7.1.4 being a more common upper end configuration for the home. However, in movie theaters and some special listening rooms I have personally counted up to 64 channels/speakers plus an entire array of subwoofers.

Clearly supporting even a moderate surround system, let alone an immersive one, takes a goodly number of speakers. Installing large numbers of speakers and subs, especially in the ceiling, can be expensive and quite a daunting task which is often frowned upon by our ‘better halves”!

So is there  another method that allows the listener to get the surround/immersive experience when there is limited space and/or no easy way to mount all those speakers? The good news is yes there is.

Enter The Soundbar

Image Credit: Sony

A Soundbar is a long rectangular speaker box that generally sits just under or in-front off your TV/display. This “single speaker” not only contains much of your systems connectivity but also all the required speakers and channel power amplifiers, and sometimes even a small subwoofer. They start from a simple 2.1 configuration and go all the way up to 7.1.2 allowing for the support of immersive sound formats like Dolby Atmos and DTS:X. Even smaller configurations have the ability support immersive formats due to their internal signal processing capabilities. All generally support the attachment of a separate sub woofer, either wired or wireless, to provide that extra “oomph”. There are many companies that manufacture these Soundbars to include Sonus, Sony, Yamaha, Samsung and LG.

Powered 7.1.2ch 500 watt sound bar/wireless system with 4K/8K passthrough, Dolby Atmos®, DTS:X, built-in subwoofer, 360 Reality Audio and works with Alexa and Google Assistant.

Sony HT-A7000

It is true to say that a dedicated receiver/processor will generally give you the best surround/immersive experience when all the speakers are correctly installed and setup. However, soundbars can provide quite a realistic experience using modern processing and directional speaker techniques, especially if the room has regular walls and ceiling surfaces that will allow the soundbars radiated sound to be “bounced” off them and back to the listening position(s).

Clearly for small rooms and apartments this arrangement provides significant appeal.

The “b” Or Sub Channel

The “b” channel or subwoofer channel is ALWAYS just a single bass channel (0.1). Music and movies are never mixed to support more than one sub channel. However, that DOES NOT mean that you only have to use one speaker on the sub channel. Also many high end receivers and processors support multiple processed sub outputs to drive multiple subs. High levels of bass need lots of air movement and that in turn means a combination of big subwoofers, lots of cone movement and/or multiple subs. It has been clearly demonstrated that the use of two or more subs (I use 4) can really improve the rooms bass performance by reducing standing waves, making the bass clearer and more evenly spread out throughout the listening area. Some AV receivers and many higher end processors therefore support multiple subwoofer outputs allowing you to easily connect multiple sub woofers. Often in lower cost receivers these are nothing more than two outputs of the same subwoofer signal. In more expensive receivers and processors each output maybe be individually fully calibrated for level, timing and EQ. BUT it is still the same signal, just optimized to drive each subwoofer based upon its room position relative to the MLP. Multiple subs need to be properly calibrated in order to optimize their combined rooms acoustic performance.

It is therefore not uncommon for receiver and processor manufactures to use a number larger than 1 for position “b“:

• 5.1 Surround sound with one subwoofer output
• 5.2 Surround sound with two subwoofer outputs
• 5.3 Surround sound with three subwoofer outputs

Remember that these ARE NOT separate bass (subwoofer) channels. There is only ever one recorded in the media.

In my case my AV system can be described as 9.4.2; nine ear height speakers, four subs and two height speakers.

For more details see my earlier posts on Introduction To Video and Audio formats On Plastic and Introduction To Audio Formats On Discs.

See Dolby Atmos® Home Theater Installation Guidelines for more details.

See DTS-X for more details.

See Auro-3D for more details.