Let’s kick off with a quick history lesson. When Al Jolson said “you ain’t heard nothin’ yet” in The Jazz Singer back in 1927, movie sound was mono – that meant one channel at the front. By 1940 Disney was experimenting with stereo for the release of Fantasia, and in the 1950s wide screen formats like CinemaScope and Cinerama added a rear channel for surround effects.
However, this kind of big screen sonic experience was restricted to large format and roadshow presentations, with your average fleapit was still using mono, or stereo if you were lucky. All that changed with Dolby Stereo, which was first introduced in 1975 and added more channels by encoding a front centre and rear surround channel within a regular stereo soundtrack.
The success of Star Wars popularised multichannel audio in cinemas, although we can thank the short-lived Sensurround system for adding a dedicated low-frequency effects channel, which is better known as ‘.1’ these days. In the early ‘90s Dolby Digital and DTS were delivering discrete 5.1 audio in cinemas and then the home, with 6.1 and 7.1 options being added in the early 2000s.
Trying to squeeze seven speakers (front left, centre and right, plus sides and rears) and a subwoofer into your lounge might require a degree of ingenuity and a sympathetic partner, but it’s certainly not impossible. From a logistical perspective things got significantly more complicated with the arrival of immersive formats like Dolby Atmos, DTS:X, IMAX Enhanced and Auro-3D.
All three approaches use height or overhead channels to create a three-dimensional hemisphere of sound around which audio objects can be seamlessly steered. As a result, the basic version of DTS:X uses up to 12 channels, Auro-3D goes to 14 channels, DTS:X Pro can go up 32 channels, and Dolby Atmos can theoretically handle 35 channels in a super-high-end system.
The idea of installing up to 35 speakers might seem like the stuff of a madman’s dreams, but with modern AV receivers including the option of Atmos decoding, and often DTS:X, it’s time to start thinking about overhead channels. Auro-3D uses a different speaker layout, and there’s virtually no content, so for the purposes of this discussion we’ll concentrate on Atmos, DTS:X and IMAX.
First of all, while the channels may be overhead that doesn’t mean you have to hang speakers from the rafters or cut holes in the ceiling – although these are options. You can also use upward-firing speakers that bounce sounds off the ceiling to create the effect of overhead channels. The lower, flatter and more reflective your ceiling, the better the results.
The majority of mid-range AV receivers offer at least nine channels of built-in amplification and 9.1-channel processing. This raises an interesting question: do you go for 5.1.4 or 7.1.2? If all those decimal points seem confusing, the first number represents the ear-level channels, the second is the LFE (Low Frequency Effects) channel and the third the overhead channels.
My recommendation would be to go with a 7.1.2 setup for two reasons: (1) with non-immersive audio soundtracks you can still enjoy up to 7.1 channels; and (2) keeping the back pair along with two overhead channels makes creating a bubble of sound easier. If you choose 5.1.4 instead, you probably won’t hear the extra overheads, but you will notice the sonic gap behind you.
So you really don’t need to be intimidated by the thought of three-dimensional audio. In fact, if you’re already rocking a 7.1-channel speaker configuration, you only need to add two overheads to immediately start enjoying the benefits. Of course, the more channels you can accommodate, the smoother the steering, but to achieve genuine immersion you don’t need to go mad.