Decades ago, most cinemas used relatively flat floors. But over the last 15 years, movie theater operators have discovered that raked seating (also known as stadium seating) not only provides a better experience, but also allows more customers to fit comfortably in the same space. Going from a flat floor layout to raked seating changes the geometry of the room—but until recently cinema audio manufacturers had not updated their designs to accommodate changes in seating configuration.
The challenges of stadium seating
A stadium seating arrangement presents significant challenges for audio system design. The loudspeakers must achieve a much greater vertical coverage angle in order to cover the audience. The rear surround speakers need to cover a rather unusual geometry, while the side surround speakers see a tilted coverage area that presents challenges.
A New Approach to Speaker Design
To address the challenges of stadium seating, cinema operators need the ability to sculpt the coverage directivity pattern to complement the room geometry. By using a speaker design that combines two high-frequency (HF) drivers in slightly different ways (Dual Dissimilar Arraying), it’s possible to create a balloon pattern that’s optimized for raked seating. This enables the speaker coverage pattern to be contoured for consistent performance at every seat in the theater.
How exactly is this achieved? Imagine for a moment that in a two-way loudspeaker, one HF driver is considered primary. A secondary driver is used to create acoustic interference and alter the coverage pattern of the primary driver, resulting in performance that is otherwise unattainable with a single driver alone. Changes in the level and timing of the secondary driver in relation to the primary driver can produce drastically different results. This is how Dual Dissimilar Arraying utilizes acoustic interference in two-way solutions like the JBL 200 Series, providing coverage precisely tuned for raked seating.
Engineering Ideal Vertical Coverage for Raked Seating
In Figure A, the green balloon represents the ideal pattern for HF coverage in a cinema with raked seating. The purple and yellow balloons represent the individual patterns created by each HF driver.
By Incorporating Dual Dissimilar Arraying as shown in Figure B, we can get exceptionally close to the target shape (in yellow) by using only two drivers. By directing sound only to where people are actually sitting, a significantly more concise coverage pattern is created, resulting in better performance.
Dual Dissimilar Arraying was first introduced in the JBL 9350 Surround Speaker System, enabling cinemas to offer a surround experience that contours to the room from the side or the rear with the flick of a switch. Designed for placement behind the screen, the JBL 200 Series uses the same technology to create a balloon pattern that perfectly fits the geometry of small and medium rooms with raked seating.