The Polk Audio MXT90BK is a Dolby Atmos-certified speaker designed to add a 3D, overhead sound dimension to your home theater by reflecting sound off the ceiling. It is sold as a pair and can be placed on top of compatible Polk speakers (like the XT20, XT60, or XT70) or wall-mounted using a keyhole slot. The speaker features a 4-inch dynamically balanced woofer and is compatible with DTS:X and DTS Virtual:X formats, requiring a minimum 7-channel AV receiver to function as a height channel.