The hd Sub15 is a compact, transportable and powerful vented subwoofer. According to extensive research in designing high-power loudspeaker chassis over the past 30 years, the new designed longexcursion chassis with 4“ voice coil and fiberglass double spider enables linear excursion up to ± 15 mm. Dramatically improved cooling of the voice coil through the pole piece and spider allows an extremely high continuous power rating. Improved cooling increases the durability and reliability of the subwoofer. Excellent dynamics and tight impulse response combined with outstanding sound pressure level is the result. Filtering is done by the Harmonic Design DSP platform. The enclosure is constructed of high-quality birch multi-plywood coated with a durable scratch-, impact- and weatherproofed polyurethane finish.