The KSLi-SUB is a high-performance cardioid subwoofer developed for integration within the d&b audiotechnik KSLi system. Purpose-built for permanent installation environments, the KSLi-SUB is engineered to deliver precise, controlled low-frequency reinforcement in applications where directivity and acoustic consistency are critical. Suitable for use in venues such as concert halls, theatres, houses of worship, and auditoriums, the KSLi-SUB is designed to supplement the full-range output of the KSLi8 and KSLi12 loudspeakers. It can be deployed in dedicated subwoofer columns or incorporated into mixed arrays when used with the appropriate mounting frame and adapter. The KSLi-SUB operates with an actively driven, two-channel bass-reflex architecture and houses three neodymium 15-inch drivers, arranged to support a cardioid dispersion pattern that significantly reduces unwanted rear energy. This enhances audience coverage while minimising reflections and structural resonance within the space. With a frequency response ranging from 36 Hz to 105 Hz, the KSLi-SUB delivers accurate low-frequency reproduction suitable for a range of demanding installation scenarios. Constructed from marine-grade plywood and finished with a weather- and impact-resistant coating, the cabinet is designed for long-term durability. Integrated rigging strands and protective metal grilles at both ends support secure installation and reliable performance over time. The KSLi-SUB stands as a critical component for audio professionals seeking high fidelity and directional control in installed sound systems.