The SL-SUB is a professional-grade subwoofer developed by d&b audiotechnik to deliver precise and powerful low-frequency reinforcement in large-scale sound systems. Designed to integrate seamlessly within the SL-Series, the SL-SUB plays a critical role in enhancing the low-end performance of line-array configurations across a wide range of professional audio applications. Utilising a dual-chamber bandpass design, the SL-SUB incorporates two forward-facing 21-inch drivers and a single rear-facing 21-inch driver, enabling precise low-frequency directivity control. This approach significantly reduces rear sound radiation, thereby improving on-stage conditions and minimising environmental impact in outdoor or acoustically sensitive environments. The SL-SUB is primarily employed in touring, festival, and fixed installation scenarios where controlled, high-output sub-bass is essential to meet the demands of modern sound design. Its robust enclosure, weather-resistant construction, and integration with d&b’s proprietary amplification and control technologies ensure reliable and consistent performance in both indoor and outdoor conditions. Whether used in a flown or ground-stacked configuration, the SL-SUB enhances the clarity and impact of the overall system, supporting accurate and intelligible sound reinforcement for audiences at scale. The SL-SUB exemplifies the precision engineering and acoustic performance standards required in professional audio environments.