Channel Proliferation

How many channels are required for surround sound? 2.1, 5.1, 7.1, 7.2.2, 9.2.4, 11.1.6? What do these numbers mean? Movie soundtracks are compatible with all of them, so what do you need?

While there are speaker bars and signal processing circuits designed to simulate the rear sound effects of a movie soundtrack with only front speakers, they can't precisely reproduce those effects for listeners in various locations. The best they can do is provide a pretty convincing illusion that some sound is coming from behind you. So I think surround sound starts with a 5.1 channel system. That's front left, center, and right speakers, left and right rear speakers, and a subwoofer (the .1 channel). In most rooms the rear speakers will be in the ceiling because that's what the room layout will allow. Few Living Rooms have symmetrical side wall locations for speakers. They may have one side wall, but the other side is open to a Kitchen or hallway. The ceiling offers an opportunity to place the speakers symmetrically around the seating area and they are usually mounted flush into the ceiling. No hanging boxes. This setup will provide most of the thrills of a movie soundtrack and is the most common version used in rooms that aren't dedicated home theaters.

The next step is 7.1 surround. This adds two more rear channels for more precise localization of surround effects. These additional 2 channels are part of the sound mix and add an enjoyable improvement to the immersive nature of surround sound. Two more surround channels means two more speakers and two more amplifier channels to drive them. Most A/V receivers from Denon, Sony, Marantz, Integra, and Yamaha have the built-in capability to power all seven speakers, but some entry-level receivers only have 5 amp channels even though they have the ability to decode 7.1 surround. You would have to add an outboard 2-channel amp if you added two more speakers later. This kind of upgrade almost never happens, so if you want a 7.1 system at least put in the wiring for four surround speakers and get an A/V receiver that can power all 7 channels. Budget permitting, you should decide which way you want to go and wire for that system, put in all the required components, and enjoy. 

Stepping up to the next level, you have 7.1.2 surround (Note: the number of subwoofers varies and is designated by the second number; so a system with 7 main channels, two subwoofers, and two height speakers would be called 7.2.2). This adds two height speakers, creating a nice vertical dimension for the surround experience. There can be more than two height speakers; the quantity is designated by the third number (7.2.4 would include four height speakers). The first two height speakers are located in the ceiling between the front speakers and your seating position. A .4 designation indicates two more height speakers behind the listening position. Height channels can also be reproduced by extra speakers built into floor-standing speakers or speaker bars, aiming upwards, bouncing the height effects off the ceiling (I wouldn't recommend this for rooms with vaulted ceilings). The addition of height speakers is commonly referred to as object-based surround technology. There are two competing formats; Dolby Atmos and DTS:X. Most movie sources (streaming and disc) have both. These very high-performance formats are more appropriate for a dedicated theater room.

There are 9.1.2, 9.2.4, 11.2.6 systems and beyond. 9 channels means they have added two front wide main speakers, which may or may not be active depending on the movie soundtrack. In a cost-no-object home theater project these can be the icing on the cake, but there are other considerations (room acoustic treatment) that are more important to the performance of a home theater. Budget will dictate the limits.

To summarize, I believe 5.1 and 7.1 systems are sufficient for most Living Room or Media Room surround systems. 7.1 systems offer a worthwhile improvement for the additional cost. 7.1.2 and higher systems are recommended for dedicated theater rooms. The precise speaker locations required to make these worthwhile need the controlled layout of a dedicated theater room, where speaker placement can be prioritized over shelves, light fixtures, door locations, and ceiling height. In other words, a room dedicated to the movie experience.

My decades of experience in designing home theater/surround sound systems for clients at various price points forms the basis for these recommendations. They are intended to help typical homeowners understand the bewildering proliferation of surround sound options on a practical level.