Developing Ultrathin Dolby Atmos® Enabled Speaker Technology for Home Entertainment Systems

Three-dimensional (3D) surround sound technology creates a premium and fully immersive audio experience for consumers. One company leading the development of such technology is Dolby Laboratories, headquartered in San Francisco, California, USA. Recently, they have been developing innovative 3D surround sound technology for TVs with the help of acoustics simulation.


By Rachel Keatley
January 2021

Raindrops splash against the tree leaves above. Toucans chirp in the distance. A rustling of branches fills your left ear. You look over and see a jaguar staring back at you. Although it may sound like you are on a trek in the Amazon rainforest, you are actually sitting in your living room watching a movie. 3D surround sound enhances the way you experience home entertainment by creating an optimal soundscape that completely envelops you in the story on the screen.

As the digital world and real world continue to blend, more consumers are expecting this type of memorable and lifelike audio experience from their home entertainment systems. Dolby Laboratories, a leading developer of innovative audio systems and technologies, is bringing 3D multidimensional audio technology to the home through their Dolby Atmos® audio format.

In 2014, Dolby Laboratories introduced Dolby Atmos® enabled speaker (DAES) technology for home theater systems and later expanded this technology for soundbar products. Now they are developing DAES technology for TVs to push the boundaries of what is possible for immersive home audio technology.

The Science of Dolby Atmos® Enabled Speakers

To reproduce realistic overhead sound, DAES technology employs an upward-firing speaker design to radiate sound upward to reflect off the ceiling, as shown in Figure 1. Perceptual filtering is applied to these speakers to amplify their sense of elevation, allowing consumers to perceive the location of sound origination as the point of reflection in the ceiling and not the physical speaker location. “If you have traditional TV speakers, you will hear the speaker's sound emitting right in front of you from the TV. With Dolby Atmos® enabled TV speakers, you will hear overhead sound coming from the ceiling,” said Lakshmikanth Tipparaju, a senior acoustic system and transducer engineer at Dolby Laboratories.

A Dolby Atmos enabled height channel speaker is located in front of a person sitting on a couch, labeled listener, and the sound is illustrated in blue going from the top of the speaker, to the ceiling, and then bouncing down toward the listener. Sound radiates upward
Figure 1. A sketch of a conventional (large form factor) height channel speaker.

Design Challenges for Ultrathin TV Speakers

If you frequently peruse the latest consumer electronics, you might have noticed that TVs get sleeker and thinner every year. Slim form factor TV design constraints make it difficult to design DAES for TVs. Why? As TV designs are made more compact, the shape and area available for the upward-firing speaker diaphragm, which is closely coupled to a boundary surface, becomes more restricted by the thickness of the TV, resulting in a narrow height channel ceiling image.

Designing slim Dolby Atmos® enabled TV speakers that are able to provide large sweet spot coverage around the typical position of a listener is a key challenge, according to Tipparaju. “A sweet spot coverage area is the region where we can consistently perceive height channel image on the ceiling. The ceiling image is compromised when we move away from the sweet spot coverage area,” said Tipparaju.

In order to design a DAES that is both thin enough to be built into modern televisions and provides large sweet spot coverage, Dolby Laboratories turned to acoustics simulation. Tipparaju believes a key benefit of simulation technology is that it allows him to evaluate the performance of new speaker designs prior to building and testing an actual physical prototype — saving valuable time and resources.

Acoustical FEM and BEM Analyses

Using acoustics modeling in the COMSOL Multiphysics® simulation software, Tipparaju explored several different upward-firing speaker design concepts for optimizing the sweet spot coverage.

“Initially, we built a speaker that was 2 inches thick,” said Tipparaju. (A typical soundbar is about 5 inches, or 12.7 centimeters, thick.) In general, it sounded pretty immersive, but we wanted to make the design more competitive." After more market research, Tipparaju and his team opted to develop a DAES that was 1 inch thick. To meet the ultrathin design constraints, they incorporated an ultrathin microtransducer (90 millimeters by 15 millimeters) into the design of the speaker. In addition, they added an acoustic reflector into the speaker's design to efficiently redistribute acoustic energy toward the ceiling — ultimately improving the speaker’s sweet spot coverage area in the process.

The model geometry of a slim height speaker with annotations at three angles: +90, 0, and -90 degrees. Slim height speaker model geometry
Figure 2. Slim height speaker with integrated acoustic reflector — directivity evaluation plane.

With acoustic finite element method (FEM) and boundary element method (BEM) functionality in the Acoustics Module, an add-on to COMSOL Multiphysics®, Tipparaju optimized the acoustic reflector topology to create an asymmetric radiation pattern to maximize the energy distribution along the ceiling direction (0 degrees to +90 degrees) and to sufficiently attenuate the direct sound (0 degree to -90 degrees) to the listener, as shown in Figure 2.

The asymmetric radiation pattern for a speaker with an acoustic reflector at different angles, from -90 to +90 degrees, visualized in rainbow with wider bands of color. SPL plot for speaker with integrated reflector
The asymmetric radiation pattern for a speaker without acoustic reflector at different angles, from -90 to +90 degrees, visualized in rainbow with narrower bands of color. SPL plot for speaker without reflector
Figure 3. Simulated vertical plane directivity comparison of a slim height speaker with an integrated reflector (left) and a conventional slim height speaker without a reflector (right). Here, it is shown that the speaker with the reflector has a wider coverage for ceiling reflection.

An FEM study was performed to optimize the acoustic reflector topology based on the vertical plane directivity in free-field, while a BEM analysis was used to numerically assess the directional response benefits of the acoustic reflector, considering TV panel integration constraints and ceiling reflections. “We want to ensure that there is uniform height channel coverage around a listener's position,” said Tipparaju. Being able to evaluate sound pressure distribution along a ceiling in simulations is very valuable, as it helps to determine the optimal left and right speaker module spacing and transducer architecture, according to Tipparaju.

A 2D graphic in black and white represents a Dolby product and a rainbow multislice plot shows the sound pressure level in dB around it. Multislice plot
Figure 4. A multislice plot depicting SPL distribution at 10 kHz in COMSOL Multiphysics®.

In their simulations, Dolby Laboratories often takes into account the different ceiling height boundary conditions. “In the United States, the typical ceiling height is about 8 to 12 feet high, and we do evaluate the speaker response at those different conditions,” said Tipparaju.

Validating the Results with a Near-Field Scanner

Based on the simulation results, physical prototypes of the slim height channel speaker with an integrated acoustic reflector were built for testing and validation.

Two real prototypes shown side-by-side: both are black and cylindrical; the left one is an ultrathin microtransducer and the right one is an ultrathin DAES. Prototypes
Figure 5. Prototype of the ultrathin microtransducer (left) and an ultrathin DAES with a 1 inch thickness (right).

The free-field sound pressure results of the FEM study were validated with experimental results from a Klippel Near-Field Scanner (NFS) measurement system. "The benefit of using a near-field scanner is that we can take fast 3D anechoic acoustic measurements in any given space or any given room," said Tipparaju.

Overall, Dolby Laboratories was able to determine that an integrated acoustic reflector can significantly improve the immersiveness of slim height channel speakers. In order to further enhance the premium, immersive audio experience for TVs, Dolby Laboratories is currently working on extending the acoustic reflector technology for side-firing surround TV speakers.

The Future of Immersive Audio Technology

“Our team's main goal is to develop different acoustic hardware systems and technologies, so that we can increase Dolby Atmos® adoption in different consumer electronic products,” said Tipparaju. In the future, Dolby plans to develop Dolby Atmos® enabled speaker technology for the smart speaker and wireless speaker market.

According to Tipparaju, this will be an interesting venture, because he will need to work closely with more compact form factors that contain microphone arrays and additional speaker(s). With the help of simulation, he plans to develop hardware solutions to improve the immersiveness in this type of system.

Acknowledgement

Lakshmikanth Tipparaju would like to thank his manager John Stewart, his colleagues within the Enhanced Consumer Devices Innovation team, and Atmos TV product management within Dolby for supporting this work.


Dolby Atmos is a registered trademark of Dolby Laboratories Licensing Corporation.