Ground Stacked Cardioid Configurations - JBL VTX Series User Manual

11.1 GROUND ST ACKED CARDIOID CONFIGURA TIONS
B18 subwoofers can be used in a variety of ground-stacked cardioid configurations, depending on available space and the number of
cabinets. The main difference between these 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, while 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 greater rejection, higher ratios yield less rejection.
Below are illustrations of front-to-back level difference curves for the two most common B18 cardioid configurations: 2:1 and 3:1. The
2:1 ratio produces a full 23dB of rejection at 50 Hz, the lowest point in its curve, while a 3:1 ratio produces a maximum of only 15dB of
rejection. Either configuration can offer excellent results, the characteristics of which depend on whether two-channel or four-channel
amplifiers are used and the quantity of available subwoofers. A 1:1 ratio generally should be avoided .
CAUTION: The level of the rear-facing subwoofers is carefully selected to allow B18 cardioid arrays to reach MAX
SPL without dynamically compromising low-frequency directivity . Do not adjust this level .
VTX B18 | User Manual
2:1 Difference Curve
15
5
0
-5
-15
-25
20Hz
3:1 Difference Curve
15
5
0
-5
-15
-25
20Hz
26
-23 dB
100Hz
-15 dB
100Hz