With the recent advent of the Dolby Atmos format we are frequently asked how best to incorporate this new object-based audio technology into a home cinema installation project. In this blog post we attempt to address the questions and issues arising from these enquiries. The majority of the information and quotations below are from Dolby themselves, specifically their Home Theatre Installation Guidelines.
Why Dolby Atmos benefits the viewing experience
“In the real world, sounds originate from all directions, not from a single horizontal plane (as per contemporary 5.1 and 7.1 channel systems). An added sense of realism can be achieved if sound can be heard from overhead.
Think of the example 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 create greater listener envelopment within the sound scene, as opposed to this sound emanating from the two-dimensional sound stage.
Another example is a 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 front to back movement, but adding overhead loudspeakers gives a much more convincing impression of the helicopter moving overhead. Adding ceiling loudspeakers also makes it possible to move sounds off the walls and into the room.”
Placement of overhead speakers within a Home Cinema System
In relation to installing a Dolby Atmos home cinema system in the home, Dolby advises the below regarding overhead speakers and their placement:
Ideal locations for typical Dolby Atmos overhead speakers:
5.1.2 or 7.1.2: Overhead speakers should be positioned at approximately 80 degrees from viewing position, and slightly ahead of it (see figure 11 and 17 from previous link).
5.1.4 or 7.1.4: Overhead speakers should be positioned at approximately 45 and 135 degrees from viewing position (see figure 13 and 19 from previous link).
Overhead (Ceiling) speakers to use
In relation to the type of speakers to be used Dolby advise: “Most conventional overhead speakers with wide dispersion characteristics will work in a Dolby Atmos home theatre.”
Whilst this is somewhat ambiguous they continue; “If the chosen overhead speakers have a wide dispersion pattern (approximately 45 degrees from the acoustical reference axis over the audio band from 100 Hz to 10 kHz or wider), then speakers may be mounted facing directly downward. For speakers with narrower dispersion patterns, those with aimable or angled elements should be angled toward the primary listening position.”
Figures for dispersion patterns are not often available from speaker manufacturers however a good quality model would certainly comply with the designated frequency range, and also in terms of off-axis dispersion.
Variations on a theme
Dolby acknowledge that while adhering to a precise specification is ideal when designing a purpose-built movie theatre (view their very interesting White Paper on the subject here), this is not always possible when integrating one into an existing family living space:
“This document does not cover all possible variables, room layouts, and factors for specific installations; adaptations and deviations may be required in particular situations. Dolby Atmos is a highly flexible solution, so minor variations from these recommendations are unlikely to materially detract from the immersive Dolby Atmos experience.”
It is useful to note that Dolby appear to have taken a common-sense approach and allowed some room for manoeuvre when installing ceiling speakers as part of an Atmos system. This is excellent news as not everyone is fortunate enough to be creating a bespoke home cinema room in their home, and flexibility is key when attempting to integrate any speaker system into a domestic environment.