JBL VTX B18 Series, User Manual

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VTX B
18 | User Manual
11.1 - GROUND STACKED CARDIOID CONFIGURATIONS
B18 subwoofers can be used in a number of ground stacked cardioid configurations depending on the available space and the number
of cabinets. The main difference between configurations is the front to back subwoofer ratio. A ratio of 1:1 indicates that there is one
rear facing subwoofer for every front facing subwoofer were a 3:1 ratio utilizes one rear facing B18 for every three front facing B18s. All
configurations use the same cardioid amplifier preset (i.e. VTX B18 80 REAR) which means that the amount of rear rejection is controlled
by the front-to-back ratio. Lower ratios produce higher rejection and higher ratios lower rejection.
Below are demonstrations of difference curves showing the front-to-back difference for the two most common B18 cardioid configura-
tions (2:1and 3:1). The 2:1 is ideal in terms of cancellation and produces 23dB of rejection at the lowest point (50Hz) were the 3:1 con-
figuration produces 15dB of rejection at the lowest point. Depending on the amplification platform (2-channel vs 4-channel amplifiers)
and available subwoofers, either configuration can be used with excellent results. In general, an 1:1 ratio should be avoided.
2:1 Difference Curve
20Hz 100Hz
-25
-15
-5
5
15
0
CAUTION: The level of the rear facing subwoofers should not be adjusted. The level was carefully selected to allow B18
cardioid arrays to reach MAX SPL without dynamically compromising low-frequency directivity.
3:1 Difference Curve
20Hz 100Hz
-25
-15
-5
5
15
0
-23dB
-15dB