Gearank

From the manufacturer:

The CVi-218S (Contra-Sub) is a portable, dual eighteen inch dedicated subwoofer system designed to extend and supplement the low frequency extension of CVi full range systems in live music and playback applications. The CVi-218S features two high power, cast frame eighteen inch transducers with 3" voice coils for extended use during high SPL applications. Steel handles and pole mount cup are also featured for use as a base for pole mounted full range systems. This configuration allows the two drivers to work together in the same acoustic space to reduce distortion components caused by driver mechanical non-linearity when the system is driven at high levels. The result is cleaner, smoother low frequency reinforcement at higher SPL levels.