JBL Control 24C Application Manual page 5

The sound system designer needs to work with the coverage over a flat listening plane – this is
called the LISTENING-PLANE coverage specification. The LISTENING-PLANE spec represents the
REALITY of the speaker's coverage for the listeners. Laws of physics dictate that the listening-plane
coverage is always more narrow than the polar coverage pattern.
By looking at the example of a speaker that has a 140 degree POLAR coverage, we can see that it
would be a mistake to assume that this speaker can cover 140 degrees over the listening plane. In fact,
the level at the edges of a 140 degree pattern is actually more than 15 dB down compared to on-axis,
NOT 6 dB. While the actual LISTENING-PLANE coverage depends on the exact characteristics of
the polar plot, the coverage of the listening plane from a speaker with a 140 degree POLAR coverage is
usually between 90 and 110 degrees.
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-15.3 dB
2
-6 dB
POLAR
POLAR
LISTENING PLANE
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LISTENING PLANE
Coverage
-6 dB
LISTENING PLANE
-6 dB
140º
140º
0 dB POLAR Reference
LISTENING PLANE
0 dB
Reference
90º
to
110°
LISTENING PLANE
-6 dB
0 dB
Reference
CEILING
-15.3 dB
CEILING