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This Technical Application Guide is intended as an adjunct to the Owner’s Manual that comes with the JBL
Control Contractor ceiling speaker. The intent is to assist sound system designers – from the new designer
to the experienced systems contractor – to design superior distributed system installations utilizing JBL
Control Contractor Ceiling Speakers.
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JBL DISTRIBUTED SYSTEM DESIGN is a software utility from JBL Professional that calculates
and displays speaker spacing and positioning of Control Contractor ceiling speakers within a rectangular
room. Several acoustical calculations are also made and the resulting document can be saved and printed.
The computations are based on actual measurements of these loudspeakers, yielding results that closely
reflect actual performance of these loudspeakers within the listening space.
Many of the calculations contained in this application guide are provided in the DSD software. It is a
convenient way to make many of these design considerations and simulate what the performance will be
for various possible design iterations.
The program can be downloaded from the JBLPRO.COM website or obtained from JBL Professional on
diskette.
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The goal in placing loudspeakers in a distributed system is to cover the area effectively, where the sound is
audible and intelligible over the entire area, and where the system is capable of sustaining the required
sound pressure level for the application type.
Understanding Coverage
The JBL Control Contractor Ceiling Speakers are designed to provide extremely even coverage on a
broadband basis over a wide coverage area. A misunderstanding of the coverage angle specifications can
easily result in mistakes being made in system designs. The COVERAGE ANGLE is defined as the
included angle at which the sound level is 6 dB down from the on-axis sound level. The coverage angle on
the listening plane is an important figure for the coverage density computations used later in this guide.
Polar vs. Listening-Plane Coverage Specifications: There are two different types of coverage
measurements which are often confused with each other. It is standard in the loudspeaker industry to
state the coverage in a “polar” pattern – in other words, in a sphere that is 1 meter from the microphone
in all directions. The angle within which the sound levels is within 6 dB of the on-axis level is called
the POLAR coverage pattern. This is a legitimate specification, but does NOT represent what the
coverage will be over a flat listening plane, such as in a room. For speakers projecting from a ceiling
onto flat listening plane, the sound has to travel farther off-axis (to the sides) than it travels on-axis
(directly below the speaker) resulting in a much greater drop-off of sound level off-axis. The end result
is that the actual coverage angle on the listening plane is more narrow than what is claimed. Some
ceiling speaker manufacturers use their POLAR measurement to claim extraordinarily wide coverage.
DO NOT use this specification to lay out coverage patterns of ceiling speakers!!!