The EVC-1181S subwoofer comprises a single 18" low frequency transducer in an optimally vented enclosure. It was created to complement the 8-, 12-, and 15-inch full range EVC systems, including the EVC-1122/VI Variable Intensity loudspeaker. Like other EVC models, the EVC-1181S subwoofer was designed and voiced to work in systems that use other EV-Innovation loudspeakers (EVF, EVH, EVA, and EVU). The EVC-1181S does not have an internal passive crossover; it requires a suitable active low pass filter and 4th-order Butterworth system high pass filter for proper operation.