Since the introduction of sound with film in 1927, there has been a steady evolution of technology used to capture the artistic intent of the motion picture soundtrack and to replay it in a cinema environment.

In 2010, the first step in enhancing digital cinema sound was undertaken with the introduction of Dolby Surround 7.1. The new format continued the pattern of increasing the number of surround channels by splitting the existing left and right surround channels into four ‘zones’.

Throughout the development of Dolby Surround 7.1, Dolby continued to investigate the future of cinema sound, working toward a new audio format. Dolby equipped dubbing theatres with various speaker configurations to determine which speaker locations are compelling to a content creator. Remixed content was then taken into different auditoria in various countries, equipped with appropriate speaker locations, to determine what is effective in theatres of varying size and shape.

INTRODUCING DOLBY ATMOS

The result of this research, Dolby Atmos, achieves unprecedented levels of audience immersion and engagement. It offers a new cinema processor featuring a flexible rendering engine that optimises the audio quality and surround effects of the Dolby Atmos soundtrack to each room’s loudspeaker layout and characteristics.

Two critical elements significantly improve the audience experience over 5.1 and 7.1 systems:
Sounds originating overhead.
Sounds originating from discrete sources throughout the auditorium. In the real world, sounds originate from all directions, not from a single horizontal plane. An added sense of realism can be achieved if sound can be heard from overhead, from the ‘upper hemisphere’.

The first example of this is of a static overhead sound, such as an insect chirping in a tree in a jungle scene. In this case, placing that sound overhead can subtly immerse the audience in the scene without distracting from the action on the screen.

Another example is a somewhat less-subtle helicopter elevating on the screen and flying off over the audience. The use of more discrete surround zones, as in Dolby Surround 7.1, helps achieve the perception of overhead movement, but adding overhead speakers prevents the brain from having to construct a phantom image of the helicopter moving overhead.

IMPROVED SURROUND DEFINITION

For many years, cinema has enjoyed having discrete screen channels in the form of left, centre, right and occasionally inner left and inner right. These discrete sources have sufficient frequency response and power handling to allow sounds to be accurately placed in different areas of the screen, and to permit timbre matching as sounds are moved or panned between locations.

In a 5.1 setup, the surround zones comprise an array of loudspeakers, all of which carry the same audio information within each left surround or right surround zone. Such arrays are particularly effective with ambient or diffuse surround effects.

However, in everyday life many sounds originate from randomly placed point sources. Being able to place such sounds discretely around the auditorium can add a heightened sense of realism without being obvious.

A fundamental role of cinema sound is to support the story on the screen. Dolby Atmos supports multiple screen channels, resulting in increased definition and improved AV coherence for onscreen sounds or dialogue.

The ability to precisely position sources anywhere in the surround zones also improves the AV transition from screen to room. If a character on the screen looks inside the room toward a sound source, the mixer has the ability to precisely position the sound so that it matches the character’s line of sight, and the effect will be consistent throughout the audience.

In contrast, in a traditional 5.1 or Dolby Surround 7.1 mix, the effect would be dependent on a viewer’s seating position. Increased surround resolution creates new opportunities to use sound in a room-centric way. This approach is an important innovation, quite distinct from the traditional approach in which content is created assuming a single listener at the ‘sweet spot’. Room-centric audio better supports the onscreen action.

INSTALLATION GUIDELINES

At present, while Dolby Atmos is primarily for commercial cinemas, content mixed in Dolby Atmos contains information describing how the audio should play back in a range of theatre configurations. This built-in adaptability will provide a foundation upon which to provide an enhanced experience in the home cinema as well.

The following guidelines, which are in large written with commercial cinemas in mind, aim to assist installers to determine where loudspeakers should be installed for the highest-quality Atmos reproduction. These guidelines do not address auditorium design, image size, acoustics, loudspeaker mounting, safety or other regulatory issues, such as building and electrical codes. Flexibility within these guidelines may be necessary to ensure that the Dolby Atmos playback is as universal and practical as possible.

Placement and elevation: The centre speaker should always be placed at the centre line of the screen regardless of the position of the screen within an auditorium. In traditionally designed cinemas, the left and right screen speakers should be positioned midway between the 1.85:1 and 2.39:1 images.

Aiming: The screen speakers should be rotated horizontally so the axis of the speaker is oriented at a point two-thirds back in the auditorium along the centre line of the image.

Screen subwoofers: Subwoofers, for low-frequency effects, should be placed on the floor behind the screen, at the rear wall junction, or flush-mounted in a screen wall. When multiple subwoofers are used, Dolby recommends they be clustered together to increase the effective efficiency though mutual coupling. The subwoofer cluster should be placed asymmetrically with respect to the centre of the room to minimise stimulation of standing waves.

Additional surrounds: One of the main differences between Dolby Atmos and Dolby Surround 7.1 and 5.1 is the position of the surround speakers. Dolby Atmos provides the ability to precisely position sound from anywhere in the auditorium. To accomplish this, additional surround speakers are added to the sidewalls and ceiling.

Side surround arrays should extend closer to the screen than previous recommended practices of loudspeaker placement, starting at one-third the distance to the back of the auditorium.

Side and rear surround spacing: For optimal spatial resolution throughout the auditorium, the angular distance between adjacent loudspeakers should be 30º or less, referenced from the midpoint between two loudspeakers at the edge of the central listening area. Loudspeaker spacing adjacent to the seating area should remain linear where possible.

Side and rear surround elevation: The side and rear surround speakers should be mounted subject to the elevation of the speaker closest to the screen matching the elevation of the acoustic centre of the screen speaker; the elevation of the speakers along the rear wall being consistent with the relative elevation of the surround closest to the screen; and, the vertical placement of the side surround speakers forming a straight line. Side and rear aiming: Side surround speakers should be tilted to orient the axis of each speaker to the seated ear height of the listener at the opposite end of the room. Rear surround speakers should be tilted to orient the axis of each loudspeaker to the seated ear height of the listener in the front row.

Top surround placement: Overhead speakers should always be placed symmetrically with respect to the centre of the screen. The overhead speakers should have the same design characteristics as the side and rear surround speakers for consistent matching timbre. It is important to ensure the projection light path isn’t obstructed by one or more of the top surround speakers. Top surround aiming: In order to provide optimum coverage, the top surround speakers should be angled laterally to a position halfway between the overhead speaker’s lateral position and the centre line of the auditorium.

Top surrounds should be angled longitudinally in the same manner as the side surrounds.

Surround speaker wiring: All surround speakers should be individually wired back to the location of the amplifiers and individually powered such that one speaker is directly connected to one channel of amplification.