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JBL 2003 CINEMA SOUND SYSTEM MANUAL
I. INTRODUCTION
The decade of the 1980’s saw many improvements in the quality of cinema sound. Dolby Laboratories
began the cinema sound revolution during the middle 1970’s with the introduction of noise reduction and
equalization of cinema loudspeaker systems to match a consistent power response standard. In 1981, JBL
demonstrated the first flat power response loudspeaker systems at the Academy of Motion Picture Arts and
Sciences. In 1983, Lucasfilm introduced the THX
®
standard screen system, along with a program of cinema
product and performance certification that covered aspects of audio and projection quality, theater-to-theater
isolation, as well as environmental acoustics. As the 1980’s progressed, Dolby stereo optical sound tracks gained
in favor, increasing the number of stereo houses significantly. The application of Dolby Spectral Recording
™
(SR)
to cinema release prints represented another step forward in sound quality.
By the mid 1990s, three digital systems had been introduced into the cinema, Dolby SR-D, Digital Theater
Sound (DTS), and Sony Dynamic Digital Sound (SDDS). These systems offered similar digital performance
characteristics, and they all provided analog stereo optical tracks for overall compatibility and operational
redundancy, should the digital portion of the system fail, or momentarily go into a mute mode. DTS makes use
of a CD-ROM running in sync with the print for its digital program, while the other two formats include the digital
information on the print itself.
As new cinema complexes are being planned and constructed, acoustical engineers are now more than
ever before being engaged to deal with problems of architectural acoustics and sound isolation between adjacent
exhibit spaces. More attention is being paid to the specification of sound equipment and its careful integration
into the cinema environment. In recent years we have seen a new trend in cinema design, stadium seating. This
facilitates a wider screen presentation, with a greater sense of audience participation.
JBL has a strong commitment to the cinema market. We have become the acknowledged leader in the
field, and our products are routinely specified for major studios and post-production houses throughout the world.
JBL continues its rapid pace in new product development aimed at increasing performance levels in the cinema.
This manual has several goals. First, it will provide a background in basic systems concepts, and
then move on to acoustical considerations in the cinema. The subject of electroacoustical specification will be
discussed, as will the problems of mounting and aiming of the components. Electrical interface and system
checkout will be covered in detail.
II. BASIC SYSTEM CONCEPTS
A. Analog Film Formats:
There are two film sizes for theatrical exhibition: 35 mm and 70 mm. The projection image aspect ratios
for 35 mm can be either 1.85:1 (“flat”) or 2.35:1 (“scope”). 70-millimeter prints are normally projected at a ratio of
2.2:1. The advantages of 70 mm have, in the past, been the availability of six magnetic tracks and large image
area. The cost of a 70 mm print is quite high, and these prints have normally been made in limited quantities for
exhibition in premier houses in large metropolitan locations. Today, the general practice with 70 mm is to use three
channels behind the screen (left, center, and right) and a single surround channel feeding multiple loudspeakers.
Options are to use the two remaining magnetic tracks for subwoofer signals and/or split (dual channel) surrounds.
The 35 mm format was modified during the 1950’s to handle four magnetic tracks: three screen channels and a
single surround channel. At the same time, the standard monophonic variable area optical track was maintained.
Figures 1A and B shows the channel layout for both 70 mm and 35 mm magnetic standards. At present, the 35
mm magnetic standard is no longer in general use.
Dolby Stereo Optical system is the standard format on non-digital 35 mm film. In this process, the dual
bilateral variable area optical sound tracks, which were formerly modulated with a monophonic signal, are
now modulated in stereo, as shown in Figure 2A. Recording on the two sound tracks is accomplished through
a matrix, which accepts inputs for the three screen channels and the single surround channel. The signals
