JBL Professional Speaker - Manual (Page 4)

Subwoofer Information
The subwoofer utility computes the number of subwoofers required to attain a comparable subwoofer
sound level within the space in a distributed in-ceiling subwoofer system.
COVERAGE – The number of subwoofers selected by CSC does NOT indicate how even the
coverage will be throughout the listening space, which is also an important consideration.
Additional subwoofers may be necessary to achieve acceptable coverage. Ceiling-mounted
subwoofers typically directly cover an area of 120 x 120 degrees. At ratios that utilize fewer
subwoofers, coverage becomes an increasingly important factor to consider. In addition, while
placement near walls and corners increases sensitivity, it can result in sound that is too loud
close to the subwoofers and too soft away from subwoofers. As rooms get larger, it is
increasingly important to cover the center of the room directly.
CROSSOVER MODE and EQ -- This chart assumes the use of a traditional active crossover that
low-passes the subwoofers and high-passes the main speakers. If main speakers are being
operated full-range (not high-passed), then a subwoofer/mains bump will occur in the frequency
response, resulting in an overly dominant mid-bass (ie, "muddy" bass). A PARAMETRIC EQ
(set with measurement software) must be utilized in the signal chain before the crossover to
remove this bump. Graphic EQs typically do not have the capability of being set to the exact
center frequency, nor can their bandwidth be adjusted to cover just the bandwidth that needs to
be reduced without overly affecting the sound.
POWERING THE SUBWOOFERS -- Ratios for Control 312CS are based on it being operated low-
impedance (8 ohms). Ratios for Control 19CS are based on it being operated either low-
impedance (19CS) or at the top 60 Watt tap (19CST). It is further assumed that the subwoofers
are driver with adequate power amplification to attain maximum SPL capability (for low-
impedance, the power amp should be rated double the speaker continuous average pink noise
power rating; for 70V/100V the power amp should be rated 20% higher than the sum of the
taps). With less amplification per subwoofer, the number of subwoofers may need to be
adjusted to a greater quantity (at an approximate ratio of doubling the quantity of subwoofers for
each halving of the amplifier power).
USING DIFFERENT JBL PRO SUBWOOFER MODELS -- JBL Professional provides a wide
variety of subwoofer choices. For systems where the chart indicates a large number of Control
312CS subwoofers, an alternative JBL subwoofer may be warranted. Choices include Control
SB210, AL6115, ASB6118 or ASB6128. Be especially mindful of coverage when using fewer
subwoofers (see "Coverage", above).