Versatile Venues: Cinemas are acoustically ready for a range of presentations

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Technology

Did you realize that movie theatres are truly multi-purpose spaces? You can conduct almost any entertainment event in a movie theatre.

Most people think that only concert halls are carefully designed for superb acoustics. They are, however, designed for a specific purpose: optimum natural reinforcement of sound occurring on the stage—natural reinforcement as opposed to electronic reinforcement via a sound reinforcement system. Each wall surface, ceiling area, room shape, seating configuration and floor system is designed to increase the sound level that is either reflected or diffused from it with the goal of making the sound level heard by the listener as strong as it can be within the constraints of the physics of sound.

As you may recall from my past columns, reverberation describes the decay of sound in a space and is a function of the room air volume and the amount and efficiency of sound absorbing finish materials in the space. Reverberation is objectively rated by a measured value known as Reverberation Time (T60, or just T), expressed in seconds. In concert halls, T60 is typically designed to be somewhere in the range of 1.8 to 2.4 seconds. Organ recital halls and large pipe organ-equipped churches will have much longer T60 values, 4.0 seconds and higher depending on the size of the room. Drama theatres and other types of live theatre spaces will be designed to 1.4 to 1.6 seconds. But try to host an organ recital in a 1.4-second live theatre and the resulting sound will be a mess, with notes designed to carry for several seconds truncated by the vast amount of sound absorption in the space! Conduct a dramatic play in a 5.0-second cathedral and you’ll have the crowd either fast asleep or gone soon after the curtain rises because the reverberation muddles the spoken word!

But cinema auditoriums really do stand alone as the only “pure” multi-purpose space. Movies have featured organ recitals and 60-instrument orchestral works, vivid drama, convocations, rallies and huge sporting events. And they all deliver the intended result of their program, all in a room designed to a T60 of less than 0.5 second. How can this be? The answer is that cinema auditoriums are designed to reduce “coloration” or natural reinforcement of sound occurring in the space. All the needed coloration of sound occurs on the state-of-the-art sound system serving the space.

The sound system can convey different reverberation times, discrete reflections (echoes) to a desired perceptual effect, ambient noise effects, and even absolute silence when called upon for dramatic or suspenseful effect. The cinema auditorium is acoustically designed to absolutely minimize the colorization of sound—within the practical limit of creating an actual anechoic chamber. (You don’t want that—a room so quiet that the only sound you hear is that of blood coursing through your head. It’s quite unsettling physically, trust me on that!)

The ceilings in cinema auditoriums are flat and sound-absorptive. They are not as absorptive as they could be—typically, mineral tile panels which absorb about half of incident sound are used instead of fiberglass panels, which absorb nearly all incident sound. The less absorptive and heavier mineral tile panels help to control noise from the HVAC ductwork and also control sound flanking between adjacent auditoriums occurring along the roof deck. All available wall areas are treated with efficient sound-absorbing panels to aid in keeping the reverberation low and also to control the creation and propagation of discrete reflections or echoes. This includes the front wall behind the screen in the auditorium, which is covered with thick sound-absorbing mineral fiber insulation material to control the creation of echoes off the loudspeakers in the room and transmitted through the perforated screen.

Some exhibitors have hosted corporate events and meetings in their auditoriums. The acoustics of a cinema auditorium are perfect for this type of function, plus the Internet and digital projection allows meetings to be simulcast and broadcast to other offices located around the world. I have also seen concerts and sporting events broadcast to remote audiences in cinema facilities. Sports franchises often conduct this type of event in the home arena or stadium, but those spaces typically have much longer reverberation times (2.5 to 4.0 seconds), so the audio feed from play-by-play and sideline broadcasters is not going to be as intelligible as it needs to be. A cinema is much better for this purpose—think of a cinema as a living room that seats 200 people!

Some exhibitors have begun teaming with videogame developers and host gaming communities with tournaments featuring team competitions and interactive videogames in their multi-screen facilities. Home theatres that these young people typically play videogames in cannot compete with the raw power and quality of a cinema sound system. And young people—seemingly all young people—spend considerable free time playing videogames. The market possibilities boggle the mind with potential!

Acoustical designer Brian Kubicki of ADK, L.L.C. may be reached at briank@adkkc.com or 913-400-3694.