The hd Sub21 is a 21" passive high-performance bass-reflex subwoofer featuring a latest-generation neodymium magnet woofer for medium to large sound reinforcement applications. The specially developed speaker basket enables extremely high sound pressure and resilience thanks to its innovative design, setting new standards in size-to-performance ratio in mobile applications or permanent installations.
Its excellent impulse behavior, rapid transient response and brutal depth are unique for a 21" subwoofer. Compared to Harmonic Design's most powerful direct radiator to date, the hd Sub18, the Sub21 is able to generate over 15 dBSPL more in the low frequency range below 35 Hz and is therefore aimed at users who require “visceral” sound pressure and headroom even in the lowest octave. The CFD flow-optimized reflex ports ensure silent operation even at maximum load.
An M20 threaded insert on the top of the cabinet allows you to screw in a support pole for additional speakers to be used in combination. In addition, four abrasion-resistant rubber feet on the underside and corresponding openings on the top ensure safe stacking of the cabinet, which is made of plywood and coated with shock and weather resistant polyurethane.
The front of the speaker is protected by a robust grille with internal acoustic foam. Large carrying handles are integrated into the side walls. On the back there are the input threads for attaching the SilentWheels hd, the acoustically decoupled 100 mm silent wheels, as well as a recessed connection panel with two NL4 sockets for connection via pin 2+/2- and input signal forwarding.
hd Sub21 can be used on all amplifiers of the Harmonic Design system to ensure reliable and precise bass reproduction.
Main features
Technical characteristics
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