SB-15121 subwoofer offers highest performance available for cinema subwoofer applications. It is designed for use in premiere cinemas and post-production applications where the ultimate in performance is required. The massive 21-inch low-frequency transducer features 6-inch diameter voice coil in a vented, neodymium magnet structure that is designed to dissipate extreme amounts of heat and allow for excursion that is double that of typical 18-inch transducers. This ensures cool operation, even at high power levels, increases driver lifespan and decreases power compression at high drive levels. The large, ported enclosure ensures response to the lowest audible frequency for bass that not only hear but also feel. The enclosure is constructed of high quality, heavily braced MDF Panels. Large, fully radiused ports ensure smooth airflow, especially at higher drive levels. This prevents potentially audible port turbulence noise. Both internal and external port openings are flared. With symmetrical port loading, the bass ports are evenly spaced around the transducer, making internal pressure more uniform across the back surface of the woofer. This prevents the cone from being displaced to one side or another by unbalanced air pressure, reducing the chance of driving the voice coil out of the center of the gap at high drive levels.