The Immersive Environment

by Keshav Nevalai | | January 10, 2022

Have you ever been so drawn into a film that you forgot you were sitting in a cinema? That transportive experience, known as “the willing suspension of disbelief”, is ultimately the goal of every filmmaker. An artistic work has done its job when it is able to pull the audience out of their day-to-day reality and into the world of the art piece. However, to fully realize that suspension of disbelief will require a proper medium through which to experience the art. In the case of film, that medium is the cinema. 

A truly great cinema transcends being just a room with some speakers and a screen. Rather than just a cinema, it becomes an immersive environment, an essential element of the experience. One in which the audience feels like they are part of the film, rather than simply an observer. While modern technologies such as Dolby Atmos have advanced the experience, providing spatial audio to enhance the off-screen experience, this does not paint the entire picture of what constitutes an immersive environment. In an immersive environment, rather than merely listening to speakers, the audience experiences a 3-dimensional field of sound. It is called Dolby ATMOS for a reason (Atmos, short for atmosphere, something in which we are immersed). It is not made up of distinct points in space but is the space itself. 

What does it take to achieve this 3-dimensional sound field?  The solution is not to cover every surface with speakers. Instead, we must create what is called a diffuse-reflective environment. Before we get into how to accomplish that, let’s look at what it means. Every room is comprised of surfaces that affect the sounds generated in that room.  These effects include reflection, diffusion, or absorption. The result of all those surface effects is the sonic experience we will have in a particular room. For this part of the discussion, we are going to look at reflection and diffusion as 2 types of reflection. A specular reflection is sonic energy that bounces off surfaces like a light off a mirror. These types of reflections, when heard in conjunction with the direct sound from the speaker can create a decorrelated image and nonlinear frequency response, thereby distorting the sound. This means the strong specular reflections, such as a first reflections off the side wall, floor or ceiling, can be perceived as another sound source and will distort the sound stage making it difficult to perceive details in the recording. This can be as bad as rendering dialog unintelligible or can be more subtle such as masking elusive, but vital, sonic details of the soundtrack.  A diffused reflection is one where the sound is scattered uniformly in many directions and therefore is not perceived as intensely. Diffused reflections support the overall listening environment while maintaining the integrity of the direct sound.  

A common mistake in our industry, in the effort to control the specular reflections, is to add too much absorption, thus reducing the room’s reverberation time (RT). The problem with this approach is that it creates an unnatural and uncomfortable listening environment.  Reverberation is a natural phenomenon so removing it from a room completely does not make for a pleasant listening experience and will make the space sound smaller than it is.  Often referred to as a ”dry” or “dead” room, such an environment is not conducive to an immersive experience. Immersion requires the listener to experience diffuse late reflections in addition to the direct sound from the loudspeakers. An overly damped room with a low RT will not provide these diffuse late reflections since most of the reflections will be absorbed before they reach the listener. Sound in such a “dead” environment will be perceived as disconnected points in space.  Quite the opposite of an immersive experience.

On the other hand, a room with a too long RT and destructive specular reflections might have a sense of envelopment but will not have the proper clarity and intelligibility. A room where the reflections are not properly diffuse will not provide that realism that immerses the audience in the sound and supports suspension of disbelief.  Instead, these distinct specular reflections decorrelate the image, distort frequency response and generally prevent the desired effect.  To create an immersive environment a room must be engineered so that the RT falls within an optimum range based on the room volume, and the reflections reaching the listener are properly diffused. The trick is knowing what materials and devices to use, how much to use and where they are best placed.

Easier said than done.  Typically, carpeting and seating provide more than adequate sound absorption needed to reduce RT to a desirable level. Unfortunately, these items are not usually in the optimum locations since effective treatments of specular reflections must be at the point of reflection between loudspeaker and listener.  So, the challenge arises from minimizing the amount of absorption used to maintain life in the room, while still treating those critical reflection points to provide an accurate listening experience. A carefully engineered mix of diffusive devices to treat high frequency reflections and absorptive devices to treat low to mid frequencies is a good practice to follow.

Speaking of best practices, designing a private cinema in general and, even more importantly, to support an immersive environment should adhere to the form follows function principal of good design.  When the chassis of the cinema is engineered first, the aesthetic elements can encase that functional form creatively, stunningly and without compromise.  The opposite sequence, aesthetics before performance, tends to compromise performance.  
Follow the function first, holistic approach which will allow for the aesthetic, “lights on” experience with the drama and anticipation it brings as well as the performance, “lights out” experience that features spectacular cinematography and, of course reality suspending immersive audio. The resulting immersive environment allows the filmmaker to deliver a transportive work of art.  Allows us to suspend our disbelief and enjoy the experience nonpareil.

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