The hd Slim265 design subwoofer is an unobtrusive sub low extension for all hd columns speakers from hd C-/M-/ML-/PL- and Beam-Series and extends the frequency range down to 55 Hz. The two 6″-long-excursion loudspeakers are specially designed for small enclosure volumes and still offer great performance with a single-role-surrounding, ferrite-magnet-system and ventilation at the pole piece for an optimum thermal dissipation at minimum power-compression. The improved cooling increases the durability and reliability of the subwoofer.