The AD-C820 and AD-C821 are acoustically identical and designed for music playback, public address and distributed audio in applications that require high output from a ceiling mounted loudspeaker. The AcousticDesign™ Series of installation loudspeakers has been designed for trouble free operation and versatility. Both models use custom designed transducers and crossover networks, in combination with an acoustically optimized enclosure (AD-C800BB), or as a fully integrated, sealed system (AD-C821). These loudspeakers continue the AD Series philosophy of bringing natural and accurate sound quality combined with versatility and reliability to high-ceiling applications. The AD-821 is a fully integrated, factory sealed system using a “dog-ear” style mounting scheme. When ordered as a system (AD-C821R SYSTEM; AD-C821S SYSTEM) a set of tile rails and a c-ring are included as is a round or square grille.