Although there are several other competing formats, all attempting to deliver a more three-dimensional approach to surround sound for movies, Dolby ATMOS certainly has the momentum with more than 100 feature films being released in the audio format over the last two years by movie studios, with cinema upgrades happening all around the world.

So what’s different?

In the real world, sounds originate from all around us, not from a single horizontal plane, so if sound can be heard from overhead, a greater sense of realism can be achieved. Dolby ATMOS steps beyond the concept of channel-based audio used in traditional multi-systems and works more on an object-based concept where content creators can precisely place and move sounds anywhere in the listening area, including overhead. As each speaker (including the surrounds) are individually addressable, filmmakers can determine exactly where a sound should be and where it should move in three dimensions.

In traditional 5.1 and 7.1 cinema systems, the surround speakers do not support the same full range frequency response or level compared to the screen speakers. A key design element of Dolby ATMOS systems is that all speakers should have similar range and level capabilities and be timbre matched. Speaker manufacturers using existing surround speaker designs for the new format have found they are not capable of producing Dolby reference levels at the main listening area and therefore won’t cut it. With specifically designed Dolby ATMOS speakers for surrounds and ceiling, the result is a clearer and more accurately positioned sound that makes entertainment incredibly realistic and lifelike.

Three critical elements significantly improve the audio experience over 5.1 and 7.1 systems:

• Sounds originating overhead.
• Improved audio quality and timbre matching.
• Greater spatial control and resolution.

Now for the Home
The big question is: how will the totally immersive experience of Dolby ATMOS that is in the commercial cinema space translate into the domestic environment? Firstly, let’s deal with the source material. The Dolby ATMOS multi-channel format will be delivered as extensions of the Dolby TrueHD and Dolby Digital Plus formats, so that the latest Blu-ray players and HDMI cables will be able to deliver the format. You just have to set your Blu-ray player’s output to Bitstream instead of PCM.

Although some preliminary information has been released by Dolby laboratories about the ATMOS format for home and a number of manufacturers are releasing compatible amplifiers between now and Christmas, the full technical specifications will not be released until CEDIA US, which took place after this article was written.

The Dolby ATMOS format for commercial cinema has a maximum capacity of 64 channels, but the home format will max out at 32 channels. The first wave of compatible amplifiers all seem to have processing for a maximum of 12 individual channels (11 channels plus the LFE channel). Most of these will require the addition of extra power amplifiers to have all channels driven.

So how are the extra speakers positioned and the channels configured in the typical home installation? The Dolby ATMOS home format will extend the existing 5.1 or 7.1 channel setup with the addition of ceiling or ceiling effect speakers characterised by adding another digit (2 or 4) to the usual convention (5.1.2, 5.1.4, 7.1.2, 7.1.4 etc.). It is these extra 2 or 4 ceiling effect speakers that will provide the added and distinctive overhead (or “Voice of God”) element to the surround mix. In other words, rather than merely encircling you with audio, ATMOS creates a dome of multi-dimensional sound over and around you. Figure 1 displays a typical 7.1.4 layout.

Dolby recommends that you use four overhead speakers when possible as this will make the placement of overhead sounds more accurate, and you’ll get more precise, realistic sounds as an object— such as a helicopter or a bird passing overhead. Two of the speakers should be in front of the listening area to the left and right and angled slightly in towards the main seating position. The other two should be positioned slightly behind the main listening position to the left and right. For smaller rooms, only two overhead speakers can be used, in which case they would be almost above but to the right and left of the main listening position. Dolby are yet to release the definitive guide to the optimal placement of these additional speakers within the room however the angles for these speakers in relation to the listing position will be critical when trying to reproduce that totally immersive experience. Figure 2 shows some possible speaker locations and relevant angles.

Most of the soon to be released Dolby ATMOS enabled receivers and amplifiers label the positioning of the ceiling speakers as Top Front Left and Right, Top Rear Left and Right, and Top Middle Left and Right, with the first two presumably being used for x.x.4 systems (four top speakers) and the latter being used for x.x.2 systems (two top speakers).

The speaker options
There are several options for the selection of speakers to suit a Dolby ATMOS system in the home. Firstly, you don’t have to sell off your existing 5.1 or 7.1 speaker system, as you can add speakers to it to achieve the ATMOS effect, although timbre matching is even more crucial to get the true immersive experience. The options are;-

Option #1: Ceiling mounted speakers firing down at the listening area

Option #2: “ATMOS Enabled” speakers with top-firing drivers that bounce the reflected sound off the ceiling to the listening area

Another possible option that has been muted is to have steerable (point able), wall mounted “ATMOS Enabled” speakers.

The ceiling mounted speakers in the first option could either be flush mounted in-ceiling speakers, (preferably with an angled baffle for the forward speakers), or surface mount ceiling speakers. Many users may be concerned with the idea of installing speakers in their ceiling, particularly if they have gone to the effort to insulate it. Slim line surface mount speakers may be the option here, remembering that with ATMOS, all speakers are recommended to deliver full frequency and full power.

For those that don’t have cable access to the ceiling, the option of the “ATMOS Enabled” speakers may be the solution. These speakers combine forward facing drivers with upward facing drivers that are designed to reflect off the ceiling to recreate the overhead sound. As this format develops, these upward firing speakers may become separate modules that can be placed on top of existing floor standing speakers.

Whether you opt for in-ceiling speakers (Dolby’s preferred solution) or upward-aiming modules or drivers, ATMOS will work best if you have a flat ceiling rather than a vaulted or angled one. The ceiling height will also play an important role in speaker selection and placement. The embodiment of the reflective concept of this design, by its very nature is complex. It is difficult to control in a domestic environment due to the differing nature of each room.

The expansion of Dolby ATMOS from commercial cinema into the domestic home theatre market is great for speaker manufacturers – they get to sell more speakers. You can bet that within twelve months there will be a myriad of options for speakers to suit this new format. Those manufacturers that have extensive experience with Dolby ATMOS in the commercial cinema market will have a jump on the rest.