The KEF Ci200QSB is a square in-wall subwoofer from KEF's Architectural range, certified to THX Ultra and THX Select standards. Designed for permanent installation within stud walls, it delivers deep, room-filling bass while remaining completely out of sight behind a flush-mounted magnetic grille. Sold as a pair, it is a natural companion to KEF's Ci Series in-wall and in-ceiling speakers in dedicated home cinema rooms where a conventional free-standing subwoofer is impractical or undesirable.
THX Certification
The Ci200QSB carries dual THX certification. In passive mode, a pair of Ci200QSBs meets THX Select specifications when driven by a suitable external amplifier. When operated in active mode with KEF's KASA500 system amplifier, two pairs achieve THX Select and four pairs achieve THX Ultra certification. THX Ultra represents the highest tier of THX certification for home cinema, targeting rooms larger than 85 square feet and demanding output levels that rival commercial screening rooms.
Driver and Acoustic Design
Each enclosure houses a single 200mm (8-inch) long-throw sub-bass driver mounted on a rigid aluminium baffle. The square footprint makes efficient use of a standard stud-bay cavity and produces a cutout of 238 x 238mm, considerably more compact than rectangular in-wall subwoofers of similar driver diameter. The aluminium baffle resists the mechanical forces generated by high bass output, preventing the structural colouration that a pressed-steel or polymer baffle would introduce at elevated levels.
Passive and Active Operation
In passive mode, the Ci200QSB connects directly to any amplifier delivering between 10 and 150 watts into 6 ohms, covering a frequency range of 40Hz to 100Hz at -6dB. The onboard passive crossover handles high-pass filtering at 100Hz, making integration with satellite speakers straightforward. In active mode, the KASA500 amplifier takes control of all crossover and equalisation duties, extending the usable response down to 18Hz and upward to 140Hz, which substantially increases output capability and low-frequency extension compared to passive operation.
Installation
Installation requires a cutout of 238 x 238mm and a mounting depth of 101.6mm (4 inches). The speaker accommodates wall or ceiling material thicknesses between 6mm and 40mm. Spring-loaded dog-leg clamps secure the baffle against the rear face of the plasterboard without requiring access to the back of the cavity. A magnetic grille snaps into place over the aluminium baffle for a clean, paintable finish. The overall chassis measures 273mm in diameter and 106mm in depth.